CELL SIGNALING & DEVELOPMENT
Target of Rapamycin (TOR) in Nutrient Signaling
and Growth Control
Robbie Loewith*,1and Michael N. Hall†,1
*Department of Molecular Biology and National Centers of Competence in Research and Frontiers in Genetics and Chemical Biology,
University of Geneva, Geneva, CH-1211, Switzerland, and
†Biozentrum, University of Basel, Basel CH-4056, Switzerland
ABSTRACT TOR (Target Of Rapamycin) is a highly conserved protein kinase that is important in both fundamental and clinical biology.
In fundamental biology, TOR is a nutrient-sensitive, central controller of cell growth and aging. In clinical biology, TOR is implicated in
many diseases and is the target of the drug rapamycin used in three different therapeutic areas. The yeast Saccharomyces cerevisiae
has played a prominent role in both the discovery of TOR and the elucidation of its function. Here we review the TOR signaling network
in S. cerevisiae.
TABLE OF CONTENTS
The Early Days1178
TOR Complex 1
Composition of TOR complex 1
Localization of TORC1
Upstream of TORC1
Physiological regulators (carbon, nitrogen, phosphate, stress, caffeine):
The EGO complex:
Feedback loop/ribosome biogenesis homeostasis:
Downstream of TORC1
Proximal TORC1 effectors:
Characterization of Sch9 as a TORC1 substrate:
Characterization of Tap42‐PP2A as a TORC1 effector:
Other TORC1 substrates:
Distal readouts downstream of TORC1:
TORC1 promotes cell growth:
Regulation of cell cycle/cell size:
Copyright © 2011 by the Genetics Society of America
Manuscript received July 29, 2011; accepted for publication September 12, 2011
Available freely online through the author-supported open access option.
1Corresponding authors: Biozentrum, University of Basel, Klingelbergstrasse 70, Basel CH-4056, Switzerland. E-mail: firstname.lastname@example.org; and Department of Molecular Biology,
NCCRs Chemical Biology and Frontiers in Genetics, University of Geneva, 30 quai Ernest Ansermet Geneva CH-1211, Switzerland. E-mail: Robbie.Loewith@unige.ch
Genetics, Vol. 189, 1177–1201December 2011
TORC1 inhibits stress responses:
Environmental stress response:
Nutrient uptake and intermediary metabolism:
Cell-wall integrity pathway:
TORC1 accelerates aging:
Less-characterized effectors identified in phosphoproteomic studies:
TOR Complex 2
Composition and localization of TOR complex 2
Upstream of TORC2
Distal readouts downstream of TORC2
What is upstream of the two complexes?
What is downstream of the TORCs?
1991, the year the last yeast monographs were published.
Coincidentally, Target Of Rapamycin (TOR) was discovered
in 1991. We thus have the whole TOR story to tell, from the
beginning, in a review that marks the 20th anniversary of
TOR. As we review TOR signaling in Saccharomyces cerevi-
siae, the reader is referred to other reviews for descriptions
of TOR in other organisms (Wullschleger et al. 2006; Polak
and Hall 2009; Soulard et al. 2009; Caron et al. 2010; Kim
and Guan 2011; Zoncu et al. 2011).
The story of the TOR-signaling network begins with a re-
markable drug, rapamycin (Abraham and Wiederrecht
1996; Benjamin et al. 2011). Rapamycin is a lipophilic mac-
rolide and a natural secondary metabolite produced by
Streptomyces hygroscopicus, a bacterium isolated from a soil
sample collected in Rapa-Nui (Easter Island) in 1965—
hence the name rapamycin. Rapamycin was originally puri-
fied in the early 1970s as an antifungal agent. Although it
effectively inhibits fungi, it was discarded as an antifungal
agent because of its then undesirable immunosuppressive
side effects. Years later, it was “rediscovered” as a T-cell
inhibitor and as an immunosuppressant for the treatment
of allograft rejection. Preclinical studies subsequently
showed that rapamycin and its derivatives, CCI-779
(Wyeth-Ayerst) and RAD001 (Novartis), also strongly in-
hibit the proliferation of tumor cells. Rapamycin received
clinical approval in 1999 for use in the prevention of organ
rejection in kidney transplant patients, and additional appli-
cations as an immunosuppressive agent have since been de-
veloped. CCI-779 (Torisel) and RAD001 (Afinitor) were
approved in 2007 and 2009, respectively, for treatment of
advanced kidney cancer. Rapamycin is effective against
tumors because it blocks the growth of tumor cells directly
and because of the indirect effect of preventing the growth
of new blood vessels (angiogenesis) that supply oxygen and
HE contributors to this GENETICS set of reviews were
asked to focus on the developments in their field since
nutrients to the tumor cells (Guba et al. 2002). Finally,
rapamycin-eluting stents prevent restenosis after angio-
plasty. Thus, rapamycin has clinical applications in three
major therapeutic areas: organ transplantation, cancer, and
coronary artery disease. What do fungi and the seemingly
very different conditions of transplant rejection, cancer, and
restenosis have in common in their underlying biology such
that all can be treated with the same drug? All three con-
ditions (and the spread of pathogenic fungi) are due to
ectopic or otherwise undesirable cell growth, suggesting
that the molecular target of rapamycin is a central controller
of cell growth. TOR is indeed dedicated to controlling cell
growth, but what is this target and how does it control cell
The Early Days
Studies to identify the cellular target of rapamycin and to
elucidate the drug’s mode of action were initiated in the late
1980s by several groups working with yeast (Heitman et al.
1991a; Cafferkey et al. 1993; Kunz et al. 1993) and mam-
malian cells (Brown et al. 1994; Chiu et al. 1994; Sabatini
et al. 1994; Sabers et al. 1995). At that time, rapamycin was
known to inhibit the vertebrate immune system by blocking
a signaling pathway in helper T cells that mediates cell cycle
(G1) progression in response to the lymphokine IL-2. How-
ever, the molecular mode of action of the drug was not
known other than it possibly involved binding and inhibiting
the cytosolic peptidyl-prolyl cis-trans isomerase FKBP12
(FK506-binding protein 12), also known as an immunophi-
lin (Schreiber 1991). Furthermore, the observation that
rapamycin inhibited cell cycle progression in yeast as in
mammalian cells suggested that the molecular target was
conserved from yeast to vertebrates and that yeast cells
could thus be exploited to identify the target of rapamycin
(Heitman et al. 1991a). It should be noted that the early
R. Loewith and M. N. Hall
researchers were interested not only in understanding rapa-
mycin’s mechanism of action, but also in using rapamycin as
a probe to identify novel proliferation-controlling signaling
pathways (Kunz and Hall 1993). In the late 1980s, signifi-
cantly less was known about signaling pathways than today;
indeed, few and only incomplete pathways were known.
The early studies in yeast first focused on identifying an
FKBP (FK506-binding protein) (Heitman et al. 1991b; Koltin
et al. 1991; Tanida et al. 1991; Wiederrecht et al. 1991).
FKBP12 had previously been identified in mammalian cell
extracts as a rapamycin (and FK506)-binding protein. Yeast
FKBP was purified to homogeneity using an FK506 column
and partially sequenced. The protein sequence information
was used to design degenerate oligonucleotides that were
then used to isolate the FKBP-encoding gene FPR1 (Heitman
et al. 1991b). The predicted amino acid sequence of yeast
Fpr1 was 54% identical to that of the concurrently charac-
terized human FKBP12, providing further support that the
mode of action of rapamycin was conserved from yeast to
humans. Curiously, disruption of the FKBP gene in yeast
(FPR1) revealed that FKBP is not essential for growth
(Heitman et al. 1991b; Koltin et al. 1991; Tanida et al.
1991; Wiederrecht et al. 1991). Additional FKBPs and cyclo-
philins (also an immunophilin and proline isomerase) were
subsequently discovered and cloned, and again single and
multiple disruptions were constructed without consequen-
tial loss of viability (Heitman et al. 1991b, 1992; Davis et al.
1992; Kunz and Hall 1993; Dolinski et al. 1997). The finding
that FPR1 disruption did not affect viability was paradoxical
because FKBP was believed to be the in vivo binding protein/
target for the toxic effect of rapamycin. Why did inhibition
of FKBP by rapamycin block growth whereas inhibition of
FKBP by disruption of the FPR1 gene have no effect on
growth? The subsequent finding that an FPR1 disruption
confers rapamycin resistance (Heitman et al. 1991a,b), com-
bined with the observation that some drug analogs are not
immunosuppressive despite being able to bind and inhibit
FKBP12 proline isomerase (Schreiber 1991), provided the
answer to the above question and led to the well-established
model of immunosuppressive drug action: an immunophilin-
drug complex (e.g., FKBP-rapamycin) gains a new toxic ac-
tivity that acts on another target. In other words, FKBP is
only a cofactor or receptor required by the drug to act on
something else; FKBP itself is not the target required for
viability. This mode of drug action also applies to the well-
known immunosuppressants cyclosporin A and FK506 (from
cyclophilin–cyclosporin A and FKBP–FK506 complexes) and
is conserved from yeast to humans (Schreiber 1991). These
early studies in yeast were the first of many that have since
contributed to an understanding of rapamycin action and
TOR signaling even in mammalian cells (Crespo and Hall
2002), illustrating that a model organism such as yeast is
valuable in both basic and biomedical research.
To identify the target of the FKBP–rapamycin complex,
rapamycin-resistant yeast mutants were selected (Heitman
et al. 1991a; Cafferkey et al. 1993). As expected, fpr1
mutants defective in FKBP were recovered, but also obtained
were mutants altered in either one of two novel genes
termed TOR1 and TOR2. The fpr1 mutations were common
and recessive. Interestingly, the TOR1 and TOR2 mutations
were rare and dominant. The TOR1 and TOR2 genes were
cloned, on the basis of the dominant rapamycin-resistance
phenotype of the mutant alleles, and sequenced (Cafferkey
et al. 1993; Kunz et al. 1993; Helliwell et al. 1994). Both
TOR1 and TOR2 proteins are 282 kDa in size (2470 and
2474 amino acids, respectively) and 67% identical. TOR1
and TOR2 are also the founding members of the PI kinase-
related protein kinase (PIKK) family of atypical Ser/Thr-
specific kinases (other members include TEL1, ATM, DNA-
PK, and MEC1) (Keith and Schreiber 1995). Although the
catalytic domain of all members of this protein kinase family
resembles the catalytic domain of lipid kinases (PI3K and
PI4K), no PIKK family member has lipid kinase activity, and
the significance of the resemblance to lipid kinases is un-
known. Two reports in 1995—before TOR was shown to be
a protein kinase—claimed that yeast and mammalian TOR
had lipid kinase (PI4K) activity, but these findings were
never confirmed and are now thought to have been due to
a contaminating PI4K. Disruption of TOR1 and TOR2 in
combination caused a growth arrest similar to that caused
by rapamycin treatment, suggesting that TOR1 and TOR2
are indeed the targets of FKBP–rapamycin and that the
FKBP–rapamycin complex inhibits TOR activity (Kunz
et al. 1993). It was subsequently demonstrated that the
FKBP–rapamycin complex binds directly to TOR1 and
TOR2 (Stan et al. 1994; Lorenz and Heitman 1995; Zheng
et al. 1995) and that TOR is widely conserved both struc-
turally and as the target of FKBP–rapamycin (Schmelzle and
Hall 2000). However, S. cerevisiae is unusual in having two
TOR genes whereas almost all other eukaryotes, including
plants, worms, flies, and mammals, have a single TOR gene.
As described below, this additional complexity in S. cerevi-
siae helped the analysis of TOR signaling because it allowed
differentiating two functionally different signaling branches
on the basis of different requirements for the two TORs.
It should be noted that there is no evidence to indicate
that FKBP has a role in normal TOR signaling, i.e., in the
absence of rapamycin. Rapamycin hijacks or corrupts FKBP
to interact with TOR. In addition, some have speculated that
rapamycin mimics an endogenous metabolite that normally
regulates TOR with or without FKBP. Although this would
provide an explanation for the evolution of the mechanism
of action of rapamycin, no evidence has been reported for an
endogenous rapamycin-like compound or for such a mode of
All TORs have a similar domain structure (Figure 1A).
The domains found in TOR—in order from the N to the C
terminus of TOR—compose the so-called HEAT repeats, the
FAT domain, the FRB domain, the kinase domain, and the
FATC domain (Schmelzle et al. 2002). The HEAT repeats
(originally found in huntingtin, elongation factor 3, the A
subunit of PP2A, and TOR1) consist of ?20 HEAT motifs,
each of which is ?40 residues that form a pair of interacting
antiparallel a-helices (Andrade and Bork 1995; Perry and
Kleckner 2003). The HEAT repeats occupy the N-terminal
half of TOR and are the binding region for subunits of the
TOR complexes (Wullschleger et al. 2005) (see below).
The central FAT domain (?500 residues) and the extreme
C-terminal FATC domain (?35 residues), flanking the FRB
and kinase domains, are always paired and found in all PIKK
family members (Alarcon et al. 1999; Bosotti et al. 2000;
Dames et al. 2005). The FRB domain (?100 residues) is
the FKBP–rapamycin-binding region. All rapamycin resis-
tance-conferring TOR mutations fall within the FRB domain,
thereby directly preventing the binding of FKBP–rapamycin
without otherwise affecting TOR activity (Heitman et al.
1991a; Cafferkey et al. 1993; Helliwell et al. 1994; Stan
et al. 1994; Chen et al. 1995; Lorenz and Heitman 1995;
Choi et al. 1996). Interestingly, all the original rapamycin-
resistance conferring mutations in TOR1 and TOR2 are mis-
sense mutations confined to a single, equivalent codon
encoding a critical serine residue (Ser1972Arg or Ser1972-
Asn in TOR1 and Ser1975Ile in TOR2) (Cafferkey et al.
1993; Helliwell et al. 1994), which explains why the
rapamycin-resistance TOR mutations were rare. Recreating
an equivalent mutation (Ser2035Ile) in mammalian TOR
(mTOR) was instrumental in demonstrating that mTOR is
the target of FKBP–rapamycin in mammalian cells (Brown
et al. 1995). Thus, the early rapamycin-resistant yeast
mutants turned out to be very informative. They not only
identified TOR, but also identified the FKBP–rapamycin-
binding site in TOR and contributed to elucidating the
mechanism of action of rapamycin. The kinase domain is
the catalytic domain and resembles the kinase domain of
PI3K and PI4K lipid kinases. Despite high interest in a struc-
ture of the kinase domain, no such structure exists for any
TOR, which is likely due to technical difficulties in express-
ing this domain for structural studies. In the absence of
a true model, a homology model based on the crystal struc-
ture of related PI3K has been elaborated (Sturgill and Hall
2009). A number of groups have identified activating, mis-
sense mutations in S. cerevisiae and Schizosaccharomyces
pombe TORs (Reinke et al. 2006; Urano et al. 2007; Ohne
et al. 2008). These mutations fall within the FAT, FRB, and
kinase domains, and, interestingly, one of the hotspots in the
kinase domain corresponds to a region for oncogenic muta-
tions in PI3K (Sturgill and Hall 2009; Hardt et al. 2011).
In the mid-1990s, research in the TOR field focused on
elucidating the cellular roles of TOR1 and TOR2. It was
found that TOR1 and TOR2 play a central role in controlling
cell growth as part of two separate signaling branches. Al-
though structurally similar, TOR1 and TOR2 are not func-
tionally identical (Kunz et al. 1993; Helliwell et al. 1994).
Combined disruption of TOR1 and TOR2, or rapamycin
treatment, mimics nutrient deprivation including causing
a G0 growth arrest within one generation (Barbet et al.
1996). Disruption of TOR1 alone has little-to-no effect,
and disruption of TOR2 alone causes cells to arrest growth
within a few generations as small-budded cells in the G2/M
phase of the cell cycle and with a randomized actin cyto-
skeleton (Kunz et al. 1993; Helliwell et al. 1994, 1998a;
Schmidt et al. 1996). These and other findings led to the
model that TOR2 has two essential functions: one function
is redundant with TOR1 (TOR shared) and the other func-
tion is unique to TOR2 (TOR2 unique) (Hall 1996; Helliwell
et al. 1998a). As described below, these two TOR2 functions
turned out to be two separate signaling branches (each cor-
responding to a structurally and functionally distinct TOR
complex) that control cell growth in different ways (Barbet
et al. 1996; Schmidt et al. 1997, 1998; Bickle et al. 1998;
Helliwell et al. 1998a; Loewith et al. 2002; Loewith and Hall
Figure 1 (A) Conserved domain structure of TOR. The N-terminal half of
TOR is composed of two blocks of ?20 HEAT repeats, 40 aa that form
pairs of interacting antiparallel a-helices. The ?500-aa FAT (FRAP-ATM-
TRRAP) domain contains modified HEAT repeats. Missense mutations in
the ?100-aa FRB (FKBP12-rapamycin-binding) domain confer complete
resistance to rapamycin. The kinase domain phosphorylates Ser/Thr resi-
dues in protein substrates, but at the sequence level resembles the cat-
alytic domain of phosphatidylinositol kinases. The ?35-aa FATC domain is
always found C-terminal to the FAT domain and is essential for kinase
activity. (B) Composition of TOR complex 1. TORC1 is ?2 MDa in size and
contains Kog1, Tco89, Lst8, and either TOR1 or TOR2. The HEAT repeats
found in Kog1 and the seven-bladed propellers of the WD-40 repeats
found in Kog1 and Lst8 are depicted. The binding of Kog1 to TOR is
complex, involving multiple domains on each protein. Lst8 binds to the
kinase domain of TOR. Each component is likely present in two copies. (C)
Composition of TOR complex 2. TORC2 is ?2 MDa in size and contains
Avo1, Avo2, Avo3, Bit61, and/or its paralog Bit2, Lst8, and TOR2 but not
TOR1. The RasGEFN domain of Avo3 and the PH domain of Avo1 are
indicated. Each component is likely present in two copies.
R. Loewith and M. N. Hall
2004; De Virgilio and Loewith 2006; Breitkreutz et al. 2010;
Kaizu et al. 2010).
The early characterization of TOR disruptions and rapa-
mycin treatment led to two more important conclusions.
First, as described in more detail below, the finding that
TOR inhibition mimics starvation led to the notion that
TOR controls cell growth in response to nutrients (Barbet
et al. 1996; Rohde et al. 2001). Subsequent studies con-
firmed this notion and demonstrated that TOR in higher
eukaryotes also controls cell growth in response to
nutrients; i.e., TOR is conserved in structure and function
(Thomas and Hall 1997; Hara et al. 1998; Schmelzle and
Hall 2000). Second, the observation that inhibition specifi-
cally of the TOR-shared signaling branch (disruption of both
TORs but not of TOR2 alone) or rapamycin treatment
mimics starvation suggested that only the TOR-shared path-
way is nutrient responsive and rapamycin sensitive (Zheng
et al. 1995; Barbet et al. 1996; Schmidt et al. 1996; Rohde
et al. 2001). The molecular basis of these findings would
remain a mystery until the discovery of the two structurally
and functionally distinct TOR complexes (see below).
The realization that TOR controls growth (increase in cell
size or mass) was a particularly important development
(Barbet et al. 1996; Thomas and Hall 1997; Schmelzle et al.
2002). Rapamycin or loss of TOR function causes a cell cycle
arrest, and TOR was thus originally thought to be a control-
ler of cell division (increase in cell number). Furthermore, at
that time, growth was largely thought to be controlled pas-
sively: i.e., the simple availability of nutrients (building
blocks) led to cell growth. As described below, the realiza-
tion that TOR controls many cellular processes that collec-
tively determine mass accumulation, combined with the fact
that there was no direct role for TOR in the cell cycle ma-
chinery then being characterized, led to the notions that
TOR controls growth and that growth is thus actively con-
trolled. The originally confusing defect in cell cycle progres-
sion observed upon TOR inhibition is in fact an indirect
effect of growth inhibition: a growth defect is dominant over
cell cycle progression.
Since the late 1990s, many groups have been character-
izing the two separate TOR2-signaling branches. It was
found that the TOR-shared signaling branch is composed
of various effector pathways that control a wide variety of
readouts that collectively determine the mass of the cell.
The readouts controlled by this branch include protein syn-
thesis and degradation, mRNA synthesis and degradation,
ribosome biogenesis, nutrient transport, and autophagy
(Schmelzle and Hall 2000). This branch is viewed as medi-
ating temporal control of cell growth. The TOR2-unique
branch controls the polarized organization of the actin cy-
toskeleton, endocytosis, and sphingolipid synthesis. This
second branch is viewed as mediating spatial control of cell
growth, on the basis largely of early work showing that it
controls the actin cytoskeleton. Thus, the logic of the two
branches appears to be to integrate temporal and spatial
control of cell growth (Loewith and Hall 2004). However,
this way of thinking about the two branches has subsided in
recent years as the TOR2-unique pathway was shown to
control sphingolipid synthesis and endocytosis in addition
to the actin cytoskeleton (Powers et al. 2010).
Another major breakthrough in the TOR field occurred in
2002: the identification of the two multiprotein complexes
termed TOR complex 1 (TORC1) and TORC2 (Loewith
et al. 2002; Wedaman et al. 2003; Reinke et al. 2004;
Wullschleger et al. 2006). The two structurally and function-
ally distinct TOR complexes were biochemically purified
from yeast cells and subsequently shown to correspond
to the two genetically defined TOR-signaling branches.
TORC1, which contains either TOR1 or TOR2 and is rapa-
mycin sensitive, mediates the TOR-shared pathway. TORC2,
which specifically contains TOR2 and is rapamycin insensi-
tive, mediates the TOR2-unique pathway. The TORCs were
a major breakthrough because they provided a molecular
basis for the functional complexity and selective rapamycin
sensitivity of TOR signaling. The biochemical identification
of the TORCs and the genetic definition of the two signaling
branches also, gratifyingly, cross-validated each other such
that there is a high level of confidence in the current “two
branch-two complex” model of TOR signaling. The subse-
quent identification of TORCs in other eukaryotes, including
plants, worms, flies, and mammals (Table 1), showed that
the two complexes, like TOR itself, are conserved and gave
further support to the above model (Hara et al. 2002;
Kim et al. 2002; Loewith et al. 2002; Jacinto et al. 2004;
Sarbassov et al. 2004). Below we focus on the structure,
function, and regulation of the two TOR complexes. We
discuss some downstream readouts of the TORCs that were
originally described before the discovery of the TORCs but
are now retroactively attributed to TORC1 or TORC2 on the
basis of their TOR requirement or rapamycin sensitivity.
TOR Complex 1
Composition of TOR complex 1
TORC1 consists of Kog1, Lst8, Tco89, and either TOR1 or
TOR2 (Figure 1B) (Loewith et al. 2002; Wedaman et al.
2003; Reinke et al. 2004). Gel filtration chromatography
(R. Loewith, W. Oppliger, and M. Hall, unpublished
results) indicated that TORC1 has a size of ?2 MDa, sug-
gesting that the entire complex is likely dimeric. This
would be consistent with the dimeric structures proposed
for TORC2 (Wullschleger et al. 2005) and mTORC1 (Yip
et al. 2010). The names of mammalian and invertebrate
orthologs of TORC1 subunits and the salient features of
S. cerevisiae TORC1 subunits are summarized in Table 1
and Table 2, respectively. Although all subunits are thought
to act positively with TOR1/2 in vivo, by and large their
functions await characterization. In the presence of rapamy-
cin, all components of TORC1 can be coprecipitated with
FKBP12 (Loewith et al. 2002), demonstrating that, unlike
mammalian TORC1 (Yip et al. 2010), the structural integrity
Table 1 TORC1, TORC2, and EGO complex orthologs in various genera
TOR1 or TOR2
Tor1 or Tor2
Orthologs listed are from Saccharomyces cerevisiae, Schizosaccharomyces pombe, Candida albicans, Dictyostelium discoideum, Arabidopsis thaliana, Caenorhabditis elegans, Dictyostelium melanogaster, and mammals. P-POD:
Princeton Protein Orthology Database/BLAST. We note that TORC2 appears to be absent in plants, e.g., A. thaliana. —, no demonstrated/obvious ortholog.
R. Loewith and M. N. Hall
of yeast TORC1 is not compromised by this macrolide. De-
spite recent molecular reconstructions from low resolution
(25 Å) electron microscopy of a TOR1–Kog1 subcomplex
(Adami et al. 2007), the molecular mechanism by which
binding of FKBP-rapamycin inhibits TORC1 activity is enig-
matic and remains a fascinating question.
Localization of TORC1
Tagging of Kog1, Tco89, Lst8, and TOR1 with GFP demon-
strates that TORC1 is concentrated on the limiting mem-
brane of the vacuole (Urban et al. 2007; Sturgill et al.
2008; Berchtold and Walther 2009; Binda et al. 2009).
These observations are consistent with previous studies that
localized TORC1 via immunogold electron microscopy and
cellular fractionation (Chen and Kaiser 2003; Reinke et al.
2004). Artificial tethering of a TORC1 peptide substrate to
the vacuole demonstrates that vacuole-localized TORC1 is
catalytically competent (Urban et al. 2007). This localization
appears to be constitutive (Binda et al. 2009), suggesting
that changes in “geography” play no obvious role in regulat-
ing yeast TORC1-signaling output. The yeast vacuole is a ma-
jor nutrient reservoir and TORC1 signaling is responsive to
nutrient cues (see below). Thus, vacuolar localization of
TORC1 seems logical. Although convincing, these studies
do not exclude the possibility that a fraction of TORC1
may also be active elsewhere in the cell. Li et al. (2006),
for example, have reported that TOR1 dynamically associ-
ateswith therDNA locus
to regulate 35S rRNA
Upstream of TORC1
Physiological regulators (carbon, nitrogen, phosphate,
stress, caffeine): A major breakthrough in the TOR field
came with the observation that rapamycin treatment alters
yeast physiology in much the same way as nutrient
starvation (Barbet et al. 1996). Like starvation, exposure
of yeast cells to rapamycin results in a dramatic drop in
protein synthesis, induction of autophagy, and exit from
the cell cycle and entrance into a quiescent G0 state. This
was the first indication that TOR, actually TORC1, might
regulate growth downstream of nutrient cues. This hypoth-
esis was strengthened when TORC1, in response to nitrogen
and carbon cues, was found to promote the sequestration of
several nutrient-responsive transcription factors in the cyto-
plasm (Beck and Hall 1999). Consistently, transcriptome
profiling demonstrated a highly similar transcriptional re-
sponse of yeast cells exposed to rapamycin, nutrient starva-
tion, or noxious stressors (Cardenas et al. 1999; Hardwick
et al. 1999; Komeili et al. 2000; Shamji et al. 2000; Gasch
and Werner-Washburne 2002). Although suggestive, these
observations provided only correlative evidence that TORC1
activity is regulated in response to environmental cues.
Characterization of a bona fide substrate of TORC1 allowed
this model to be tested directly.
As detailed below, Sch9 presently remains the best-
characterized substrate of TORC1, and monitoring its phos-
phorylation by Western blotting serves as a convenient proxy
for TORC1 activity. In addition to exposure to rapamycin,
Sch9 is rapidly dephosphorylated in cells experiencing acute
starvation of carbon, nitrogen, phosphate, or amino acids
(Urban et al. 2007; Binda et al. 2009). These and other obser-
vations confirm that TORC1 is responsive to both the abun-
dance and the quality of nutrients in the environment; but,
with few exceptions (see The EGO complex), how nutrient
cues are sensed and how this information is transduced to
TORC1 remain unknown.
TORC1 activity is also regulated in response to noxious
stressors. When cells are subjected to various stress con-
ditions, including high salt, redox stress, a shift to a higher
temperature, or caffeine, Sch9 phosphorylation is reduced
dramatically (Kuranda et al. 2006; Urban et al. 2007). With
the exception of caffeine, which directly inhibits TORC1
Table 2 Salient features of TORC1 components
ProteinSizeMotifs/domains Potential function
TOR1 2470 aa HEAT repeats, FAT domain, FRB domain,
kinase domain, and FATC domain
HEAT repeats, FAT domain, FRB domain,
kinase domain, and FATC domain
An N-terminal conserved region 4, HEAT
repeats, 7 C-terminal WD-40 repeats
7 WD-40 repeats
Protein kinase, scaffold
TOR2 2474 aaProtein kinase, scaffold
Kog1 1557 aaPresent substrate to TOR
Receive signals from EGO complex
Stabilize kinase domain
Table 3 Salient features of EGO Complex components
ProteinSize Motifs/domains Potential function
Transmembrane domain, PtdIns(3,5)P2 bindinga
GTP-bound form activates TORC1
GDP-bound form activates TORC1
aDescribed in Dubouloz et al. (2005), Hou et al. (2005), and references therein.
kinase activity (Kuranda et al. 2006; Reinke et al. 2006;
Wanke et al. 2008), how environmental stress signals are
transduced to TORC1 is also unclear.
The EGO complex: When environmental conditions are in-
appropriate for growth, cells stop dividing, slow their me-
tabolism, induce the expression of stress-responsive proteins,
and accumulate energy stores. This nondividing but meta-
bolically active state is known as quiescence (G0). How cells
enter into quiescence is relatively well characterized. In
contrast—and despite its medical relevance (inappropriate
exit from quiescence can lead to cancer or reactivation of
a latent infection)—how quiescent cells reinitiate growth is
poorly understood. To shed light on this process, a clever
screen was performed to identify mutants that are unable to
escape from rapamycin-induced growth arrest (EGO)
mutants (Dubouloz et al. 2005). This and a follow-up study
(Binda et al. 2009) identified the EGO complex as an impor-
tant regulator of TORC1.
The EGO complex is composed of four proteins: Ego1,
Ego3, Gtr1, and Gtr2 (Table 3 and Figure 2). Gtr1 and
Gtr2 are Ras-family GTPases and orthologs of the metazoan
Rag GTPases (Kim et al. 2008; Sancak et al. 2008) (Table 1).
Although they lack obvious sequence homologies, Ego1 and
Ego3 are likely the functional homologs of vertebrate p18
(LAMTOR1) and p14 + MP1 (LAMTOR2 + LAMTOR3),
respectively, which function together as the “Ragulator”
complex (Kogan et al. 2010; Sancak et al. 2010). Ragulator
and the Rags mediate amino acid sufficiency signals
to mTORC1 (reviewed in Kim and Guan 2011). Like its
mammalian counterpart, the EGO complex resides on the
vacuolar/lysosomal membrane and is thought to couple
amino acid signals to TORC1 (Binda et al. 2009). Curiously,
the Gtr1GTPGtr2GDPcombination activates TORC1 with the
nucleotide-binding status of Gtr1 seemingly dominant over
the nucleotide-binding status of Gtr2.
TORC1 activity in both metazoans and yeast appears to
be particularly responsive to glutamine (Crespo et al. 2002)
and the branched-chain amino acid leucine (Binda et al.
2009; Cohen and Hall 2009). In yeast, leucine starvation
destabilizes Gtr1-TORC1 association and causes a reduction
in Sch9 phosphorylation whereas GTP-locked Gtr1Q65L
remains bound to TORC1 and Sch9 dephosphorylation is
delayed in cells expressing this mutant (Binda et al. 2009).
Loss of Gtr1 results in reduced Sch9 phosphorylation and
slow growth whereas GDP-locked Gtr1S20Lis dominant neg-
ative. When Gtr1S20Lis expressed as the sole version of Gtr1,
cells are extremely sick. This near inviability is suppressed
by deletion of the TCO89 gene encoding the TORC1 subunit
Tco89. Collectively, these observations suggest that the EGO
complex can both positively and negatively regulate TORC1
activity via Tco89. The fact that the EGO complex can neg-
atively regulate TORC1 activity seems to be at odds with the
current metazoan model according to which the EGO com-
plex counterpart serves only to localize TORC1 to the vacu-
ole. Indeed, in contrast to the results obtained in metazoans,
in yeast, TORC1 appears to stably localize to the vacuolar
membrane regardless of nutrient conditions. Thus, how the
EGO complex influences TORC1 activity remains a mystery
although the crystal structure of the Gtr1–Gtr2 complex,
reported very recently, provides some mechanistic insights
(Gong et al. 2011).
Also mysterious are the mechanisms by which amino acid
sufficiency modulates Gtr1/2 guanine nucleotide loading.
Given its localization, it is tempting to postulate that the
EGO complex responds to levels of intravacuolar amino
acids, possibly via the recently described Gtr1 guanine–
nucleotide exchange factor (GEF) Vam6/Vps39 (Binda
et al. 2009). It is equally plausible, however, that this signal
is mediated by an as-yet-unidentified GTPase-activating pro-
tein (GAP) activity. Consistent with the conserved function
of the EGO/Ragulator complex, and like its yeast ortholog,
hVPS39 has been found to function positively upstream of
mTORC1 (Flinn et al. 2010).
Feedback loop/ribosome biogenesis homeostasis: Although
most recognized as a target of signals emanating from
extracellular nutrients and noxious stresses, it is becoming
increasingly apparent that TORC1 also responds to intracel-
lular cues. In addition to the sensing of intracellular amino
acids as described above, outputs from distal effectors also
regulate TORC1 in apparent feedback loops. For example,
in both yeast and mammalian cells, it is well documented
that TORC1 activity stimulates translation initiation
Figure 2 The EGO complex is a major regulator of TORC1. The EGO
complex (EGOC) is composed of four proteins: the palmitoylated and
myristolated protein Ego1, the transmembrane protein Ego3, and two
Ras-family GTPases, Gtr1 and Gtr2. Like TORC1, the EGO complex is
localized to the vacuolar membrane where it appears to sense/respond
to intracellular leucine levels and potentially to intravacuolar amino acid
levels. Vam6 has been identified as a guanine nucleotide exchange factor
for Gtr1 but no other GEFs or GAPS for this GTPase system have been
reported. In the Gtr1GTPand Gtr2GDPconfiguration, the EGO complex
somehow activates TORC1; the reverse conformation inactivates TORC1.
Activated TORC1, via its two main effector branches, the AGC kinase
Sch9 and the Tap42-PP2a and PP2a-like protein phosphatases, stimulates
growth by favoring anabolic processes and by antagonizing catabolic
processes and stress-response programs.
R. Loewith and M. N. Hall
(Wullschleger et al. 2006). Interestingly, inhibition of trans-
lation with cycloheximide causes a pronounced increase in
(m)TORC1 activity presumably by triggering an increase in
the concentration of free amino acids in the cytoplasm
(Beugnet et al. 2003; Urban et al. 2007; Binda et al.
2009). Ribosome biogenesis (described in more detail be-
low) is a second example. TORC1 regulates ribosome bio-
genesis in part via two substrates, Sch9 and the transcription
factor Sfp1. Reduced ribosome biogenesis resulting from de-
letion of SCH9 or SFP1 results in a dramatic increase in
TORC1 activity (Lempiainen et al. 2009). It is possible that
blocking ribosome biogenesis, like translation inhibition,
causes an increase in free amino acids that subsequently
activates TORC1. Alternatively, other mechanisms could be
at play. Regardless of mechanism, such feedback loops pro-
vide an elegant means by which growth homeostasis can be
maintained by TORC1.
Downstream of TORC1
In general terms, when growth conditions permit, TORC1
is active and its signals promote the accumulation of cel-
lular mass. However, as both proximal and distal TORC1
effectors continue to be described, the extent of this tem-
poral regulation of growth control is only starting to be
Proximal TORC1 effectors: Characterization of Sch9 as
a TORC1 substrate: Arguably, the best-characterized sub-
strates of both yeast and metazoan TOR complexes are the
AGC family kinases. This rather well-studied family of
kinases is so named on the basis of its mammalian members
PKA, PKG, and PKC (Pearce et al. 2010). Typically, activation
of AGC family kinases requires phosphorylation of two con-
served regulatory motifs, the “T,” or “activation,” loop lo-
cated in the catalytic domain and the “hydrophobic” motif
found toward the C terminus. Phosphorylation of these
motifs helps stabilize the kinase domain in an active confor-
mation. Several AGC family kinases additionally contain
a “turn” motif located between the kinase domain and the
hydrophobic motif, phosphorylation of which is thought to
promote protein stability. While the T loop is phosphorylated
by PDK1 or its ortholog Pkh in mammalian or yeast cells,
respectively, phosphorylation of the hydrophobic and possi-
bly the turn motifs is often mediated by TORC1 or TORC2.
Analogous to S6K for mTORC1, the AGC kinase Sch9 was
recently found to be a direct substrate for yeast TORC1
(Powers 2007). Six target sites in the C terminus of Sch9
are phosphorylated by TORC1: Thr737 found in a classical
hydrophobic motif; Thr723 and Ser726, Ser/Thr-Pro sites
found in what appears to be a turn motif; Ser758 and
Ser765 found in sequences that resemble the hydrophobic
motif; and Ser711 in a region that partially resembles a hy-
drophobic motif. TORC1-mediated phosphorylation is nec-
essary for Sch9 activity. Replacing the target amino acids
with alanine yields a nonfunctional Sch9, whereas replacing
them with a phosphomimetic residue confers constitutive
kinase activity, i.e., activity even in the absence of TORC1
(Urban et al. 2007). Presumably, phosphorylation of the turn
motif helps to stabilize Sch9 while phosphorylation of the
hydrophobic motif stabilizes Sch9 in an active conformation.
Curiously, although their in vivo functions are unknown,
in vitro TORC1 preferentially phosphorylates Ser758 and
Ser765 within the hydrophobic-like motifs (R. Loewith, un-
published results). That TORC1 can phosphorylate amino
acids found within such diverse sequence contexts, which
is rather atypical for protein kinases, is also curious.
Characterization of Tap42‐PP2A as a TORC1 effector: In
addition to Sch9, TORC1 also regulates type 2A (Pph21,
Pph22, and Pph3—generically PP2Ac) and 2A-related phos-
phatases (Sit4, Ppg1). These partially redundant yet pleio-
tropic enzymes are notoriously difficult to study. Analysis of
Sit4 function, and therefore of TORC1 function, is further
complicated by strain-dependent polymorphisms at the
SSD1 (Suppressor of SIT4 Deletion) locus (Reinke et al.
A role for these phosphatases downstream of TORC1 was
first described by the Arndt lab (Di Como and Arndt 1996).
In this work, a subpopulation of these enzymes was found to
interact in a TORC1-dependent manner with a regulatory
protein known as Tap42. Rrd1 and Rrd2, two peptidyl-
prolyl cis/trans isomerases, were subsequently also found
to be present in these Tap42 complexes (Zheng and Jiang
2005; Jordens et al. 2006). Work, done in large part by the
Jiang group, posits that when TORC1 is active, Tap42 is
phosphorylated and bound tightly to the phosphatase–Rrd
complex (Di Como and Arndt 1996; Jiang and Broach 1999;
Zheng and Jiang 2005). Inactivation of TORC1 results in
Tap42 dephosphorylation and a weakened association with
phosphatases that presumably results in their activation
and/or change in substrate preference (Duvel et al. 2003;
Yan et al. 2006). How TORC1 maintains Tap42 phosphory-
lation is mechanistically unclear. It may phosphorylate
Tap42 directly (Jiang and Broach 1999), or it may act via
the Tap42 interacting phosphoprotein Tip41 (Jacinto et al.
2001). Interestingly, Tip41 has been proposed to both an-
tagonize and cooperate with Tap42 in controlling TORC1
signaling (Jacinto et al. 2001; Kuepfer et al. 2007).
Although the mechanisms coupling TORC1 to Tap42–
PPase complexes remain to be elucidated, genetic argu-
ments clearly position Tap42 as a prominent effector of
TORC1. Specifically, several alleles of TAP42 (e.g., TAP42-
11) that confer strong resistance to rapamycin by blocking
a subset of rapamycin-induced readouts have been identi-
fied (Di Como and Arndt 1996; Duvel et al. 2003).
Curiously, TAP42-11 does not provide rapamycin resis-
tance in all strain backgrounds. However, co-expression of
genetically activated Sch9 (described above) in rapamycin-
sensitive TAP42-11 backgrounds results in a very strong syn-
thetic resistance to rapamycin (Urban et al. 2007). From this
observation, it appears that Sch9 and Tap42-PPase com-
plexes are major effector branches downstream of TORC1
with each branch, at least in some backgrounds, performing
one or more essential function. The readouts mediated by
these two TORC1 branches are discussed below.
Other TORC1 substrates: In addition to the regulation of
these two major effector branches, TORC1 has been
reported to directly phosphorylate other substrates includ-
ing Sfp1(Lempiainen et al. 2009), Gln3 (Bertram et al.
2000), and Atg13 (Kamada et al. 2010). The roles that these
proteins play downstream of TORC1 are discussed below.
Tyers and colleagues have recently defined a global
protein kinase and phosphatase interaction network in yeast
(Breitkreutz et al. 2010). This study, consisting of affinity
purification followed by mass spectrometry, included TOR1
and TOR2. They found and confirmed that TORC1 physi-
cally interacts with the following proteins: Mks1, a protein
involved in retrograde (RTG) mitochondria-to-nucleus sig-
naling (see below); curiously, FMP48, an uncharacterized
protein presumed to localize to the mitochondria (Reinders
et al. 2006); Npr1, a protein kinase involved in the intracel-
lular sorting of nutrient permeases (see below); Ksp1,
a protein kinase involved in nutrient-regulated haploid fila-
mentous growth (Bharucha et al. 2008); Nap1, a chromatin
assembly factor and a mitotic factor involved in regulation of
bud formation (Calvert et al. 2008); Nnk1, the nitrogen
network kinase presumably involved in intermediate nitro-
gen metabolism (Breitkreutz et al. 2010); Sky1, an Ser/Arg
domain kinase involved in pre-mRNA splicing (Shen and
Green 2006); and Bck1 and Kdx1, which are involved in
MAPK signaling (Breitkreutz et al. 2010). Given their phys-
ical interaction with TORC1, all of these proteins, in addi-
tion to multiple other, as-yet-unconfirmed interactors, are
potential substrates (or regulators) of TORC1. These results
underscore the central role that TORC1 plays in cell growth.
Distal readouts downstream of TORC1: TORC1 promotes
cell growth: When environmental conditions are favorable,
TORC1 coordinates the production and accumulation
of cellular mass, i.e., growth, via regulation of several
Protein synthesis: The first realization that TORC1 serves
to couple environmental cues to the cell growth machinery
came with the observation that rapamycin treatment elicits
a marked drop in protein synthesis by blocking translation
initiation (Barbet et al. 1996). A major target for this regu-
lation appears to be the translation initiation factor eIF2.
Upon amino acid starvation or rapamycin treatment, the
a-subunit of eIF2 is phosphorylated and this dominantly
interferes with 59CAP-dependent mRNA translation
(reviewed in Hinnebusch 2005). TORC1 signals to eIF2a
via both the Sch9 and Tap42-PPase branches. The sole
eIF2a kinase is the conserved Gcn2 protein. Gcn2 binds
and is activated by uncharged tRNAs that accumulate when
cells are starved for an amino acid (detailed below).
Gcn2 activity is also regulated by phosphorylation.
Gcn2 phosphorylation on Ser577 reduces tRNA binding
and, consequently, kinase activity. Treating cells with rapa-
mycin elicits a rapid, Tap42-PPase-dependent dephosphory-
lation of Ser577 and, consequently, an increase in Gcn2
activity and a reduction in 59CAP-dependent translation
(Cherkasova and Hinnebusch 2003). It is possible that one
or more Tap42-associated phosphatases directly dephos-
phorylates Ser577, but this has not been formally demon-
strated. The nature of the kinase that phosphorylates Gcn2
Ser577 is unknown other than it is not Sch9 (M. Stahl and
R. Loewith, unpublished results). Sch9 inhibition, however,
also leads to eIF2a phosphorylation via an undefined path-
way (Urban et al. 2007).
Studies with rapamycin suggest that, in addition to
eIF2a, TORC1 may target additional translation factors
such as the 59CAP-binding protein (eIF4E) interacting pro-
teins Eap1 and/or the eIF4G scaffold (Berset et al. 1998;
Cosentino et al. 2000). Finally, recent phosphoproteomics
studies (Huber et al. 2009; Loewith 2010; Soulard et al.
2010) have identified several translation-related proteins
whose phosphorylation is altered by rapamycin treatment,
suggesting that these factors could also couple TORC1 to
Ribosome biogenesis: In optimal conditions, yeast cells
grow and divide approximately every 100 min. Such rapid
growth requires robust protein synthesis, which of course
requires ribosomes. Indeed, rapidly growing yeast cells
contain ?200,000 ribosomes, implying that each cell must
produce and assemble ?2000 ribosomes per minute
(Warner 1999). This is not a trivial feat as each ribosome
contains 78 unique proteins (encoded by 137 RP genes) in
addition to four rRNA molecules, three derived from the
RNA Pol I-transcribed 35S pre-rRNA and one transcribed
by RNA Pol III. Fifty percent of RNA Pol II transcription is
devoted to ribosomal proteins. In addition, numerous pro-
tein and small RNA trans-acting factors, known as ribosome
biogenesis (RiBi) factors, are required for the correct pro-
cessing, folding, assembly, nuclear export of pre-ribosomal
particles to the cytoplasm, and final maturation events into
40S and 60S particles. The production of all these abundant
molecules represents a huge energetic investment. Not sur-
prisingly, yeast cells have developed elaborate measures to
coordinate the expression of rRNA, tRNA, RPs, and RiBi
factors in response to environmental conditions. Much of
this regulation is mediated by TORC1 at the level of tran-
scription. As ribosome biogenesis has clear links to diseases
such as cancer, anemia, and aging, dissection of its regula-
tion will undoubtedly have clinical ramifications (Lempiainen
and Shore 2009).
In S. cerevisiae, the rDNA locus consists of ?150 tandemly
repeated transcription units on chromosome XII, and yet
rRNA production is still limiting for cell growth (Warner
1999). Each of these rDNA units comprises the RNA poly-
merase III transcribed 5S rRNA gene, the intergenic spacer
region, and the RNA Pol I-transcribed 35S rRNA gene,
encoding the 35S precursor of the mature 18S, 5.8S, and
25S rRNAs. RNA Pol III also transcribes tRNA genes as well
as several additional genes encoding small noncoding RNAs.
In the late 1990s, it was reported that rapamycin results in
R. Loewith and M. N. Hall
a rapid and pronounced drop in 5S, 35S, and tRNA produc-
tion (Zaragoza et al. 1998; Powers and Walter 1999). Re-
cently, the relevant signaling pathways in this regulation
have become clearer.
TORC1 regulates the accumulation of RNA Pol I tran-
scripts at multiple levels. Processing of the 35S pre-rRNA
occurs cotranscriptionally and is dependent on the presence
of ribosomal proteins (Tschochner and Hurt 2003). The fast
drop in RNA Pol I-dependent transcripts observed upon
rapamycin treatment is apparently due to decreased trans-
lation (described above) of ribosomal proteins (Reiter et al.
2011). The majority of mRNAs being translated in a rapidly
growing cell encode ribosomal proteins (Warner 1999), and
thus a drop in translation will rapidly reduce the levels of
free ribosomal proteins that are themselves needed stoichio-
metrically for processing of rRNA into pre-ribosome par-
ticles. rRNA that is not efficiently processed is immediately
degraded, presumably to prevent imbalances in structural
components of the ribosome. At later time points following
rapamycin treatment, RNA Pol I no longer associates with
the rDNA and transcription stops. This late effect could be
the result of rapamycin-induced degradation of the essential
RNA Pol I transcription factor Rrn3 (Claypool et al. 2004;
Laferte et al. 2006; Reiter et al. 2011).
TORC1 regulates RNA Pol III apparently exclusively via
Sch9 and a repressor protein named Maf1 (Upadhya et al.
2002; Oficjalska-Pham et al. 2006; Reina et al. 2006; Huber
et al. 2009; Lee et al. 2009). Sch9 directly phosphorylates
seven sites in Maf1 that prevent it from interacting with and
thus inhibiting RNA Pol III (Vannini et al. 2010). Phospho-
mimetic variants of Maf1 clearly fail to associate with RNA
Pol III, but, curiously, Sch9 inhibition still causes a reduction
in RNA Pol III activity in these strains but not in maf1D
strains. This and other observations suggest that an addi-
tional Sch9 target exists that, when dephosphorylated,
represses RNA Pol III in a Maf1-dependent fashion (Huber
et al. 2009; Michels 2011). Maf1 is conserved and also func-
tions downstream of mTORC1 to regulate RNA Pol III activ-
ity. However, in mammalian cells, and perhaps in yeast cells
too, Maf1 is directly phosphorylated by mTORC1 rather
than by the Sch9 ortholog S6K1 (Wei et al. 2009; Wei and
Zheng 2010; Michels 2011).
A total of 137 genes encode the 78 proteins that make up
a yeast ribosome (most RPs are encoded by two genes
yielding nearly identical proteins). TORC1 coordinately
regulates the expression of these genes through several
mechanisms (Figure 3) (Lempiainen and Shore 2009). A
central component of this regulation is the Fhl1 protein
(Lee et al. 2002; Martin et al. 2004; Schawalder et al.
2004; Wade et al. 2004; Rudra et al. 2005). Fhl1 has a fork-
head DNA-binding domain, and its constitutive association
to ribosomal protein gene (RP) promoters is facilitated by
the DNA-binding protein Rap1 and the high mobility group
protein Hmo1 (Hall et al. 2006; Berger et al. 2007). TORC1
regulates RP transcription by determining the association
between Fhl1 and either one of two FHB-containing pro-
teins, Ifh1 and Crf1. Both Ifh1 and Crf1 are phosphopro-
teins. When cells are growing and TORC1 is active, Ifh1 is
phosphorylated and binds to Fhl1 to stimulate RP transcrip-
tion. Conversely, inhibition of TORC1 results in the phos-
phorylation of Crf1, which displaces Ifh1 to repress RP
transcription. The signaling events upstream of Ifh1 are
not known, whereas TORC1 seems to signal to Crf1 via
the Ras/PKA pathway target Yak1 (Martin et al. 2004).
However, it should be noted that the crosstalk between
TORC1 signals and Ras/PKA signals has been debated.
While it is clear that hyperactivation of Ras/PKA can sup-
press many rapamycin-induced phenotypes (Schmelzle et al.
2004), suggesting that PKA is downstream of TORC1, it has
also been proposed that TORC1 and PKA signal in parallel
Figure 3 Control of RiBi and RP gene transcription by
TORC1. RiBi factors are required for the proper expression,
processing, assembly, export, and maturation of rRNA and
RPs into ribosomes. This energetically costly procedure is
under tight regulation, particularly at the transcription
level. TORC1 regulates RiBi and RP gene transcription via
multiple pathways: (1) TORC1 directly phosphorylates the
Split Zn-finger transcription factor Sfp1, which presumably
regulates its nuclear localization and/or binding to RP and
possibly RiBi gene promoters to stimulate their expression.
(2) Fhl1 and Rap1 bind constitutively to RP promoters.
When TORC1 is active, phosphorylated Ifh1 binds to
Fhl1 to stimulate transcription, possibly by recruiting the
NuA4 histone acetyltransferase. When TORC1 is inactive,
Yak1 phosphorylates Crf1, which subsequently outcom-
petes Ifh1 for binding to Fhl1. (3) Sch9 phosphorylates
and thus inhibits Stb3 and the paralogs Dot6 and Tod6.
Inhibition of TORC1/Sch9 results in the dephosphorylation
of these three transcription repressors, which subsequently
bind to RRPE and PAC elements found in RiBi promoters.
Stb3 additionally binds RP promoters. Bound to pro-
moters, these repressors recruit the RPD3L histone deace-
tylase complex to repress transcription.
pathways that impinge on common targets (Zurita-Martinez
and Cardenas 2005; Ramachandran and Herman 2011). Re-
cently, Soulard et al. (2010) have provided some clarifica-
tion of this dilemma by proposing that TORC1 functions
upstream of PKA but only for a subset of PKA targets. Thus,
TORC1 may be both upstream and parallel to PKA.
TORC1-dependent regulation of RP gene transcription
still occurs in the absence of the Fhl1/Ifh1/Crf1 system,
suggesting the existence of additional regulatory mecha-
nisms. One of these is the split zinc (Zn)-finger protein
Sfp1 (Fingerman et al. 2003; Jorgensen et al. 2004; Marion
et al. 2004; Lempiainen et al. 2009; Singh and Tyers 2009).
TORC1 binds and directly phosphorylates Sfp1 to promote
its binding to a subset of RP gene promoters. Curiously, un-
like Sch9, TORC1-mediated Sfp1 phosphorylation appears
to be insensitive to osmotic or nutritional stress, suggesting
that TORC1 regulates these two substrates via very different
mechanisms (Lempiainen et al. 2009). Sfp1 also interacts
with the conserved Rab escort protein Mrs6, an essential
protein functioning in membrane sorting (Lempiainen
et al. 2009; Singh and Tyers 2009). Sfp1-Mrs6 association
is important for the nuclear localization of Sfp1, but its
functional implications are otherwise unclear. Intriguingly,
this association may underlie the presently unexplained
genetic and biochemical interactions between TORC1 and
vesicular transport machineries (Aronova et al. 2007; Zurita-
Martinez et al. 2007). Although physical interaction with
RiBi promoters has not been reported, overexpression of
Sfp1 causes a rapid upregulation of most RiBi genes, sug-
gesting that Sfp1 also regulates this important regulon
(Jorgensen et al. 2004). Better understood is the regulation
of RiBi gene expression downstream of Sch9. RiBi promoters
typically possess polymerase A and C (PAC) and/or ribo-
somal RNA processing element (RRPE) elements. PAC ele-
ments are bound by the myb-family transcription factors
Dot6 and Tod6 (Freckleton et al. 2009; Zhu et al. 2009)
whereas RRPE elements are bound by Stb3 (Liko et al.
2007). Stb3 seems to bind to T-rich elements in RP pro-
moters as well (Huber et al. 2011). All three transcription
factors are phosphorylated by Sch9 and thus are under
TORC1 control (Lippman and Broach 2009; Liko et al.
2010; Huber et al. 2011). When TORC1 is inactivated,
Dot6, Tod6, and Stb3 are dephosphorylated, allowing
them to bind to their cognate promoter elements and recruit
the RPD3L histone acetyltransferase complex to repress
In summary, TORC1 plays a central role in regulating
ribosome biogenesis, particularly at the transcriptional level.
However, it is now clear that TORC1 also influences ribosome
biogenesis post-transcriptionally. Phosphoproteomics as well as
more directed studies suggest that TORC1 regulates various
catalytic steps of ribosome assembly per se (Honma et al. 2006;
Huber et al. 2009; Loewith 2010). Phosphoproteomics and
biochemical studies (Albig and Decker 2001; Grigull et al.
2004; Huber et al. 2009; Breitkreutz et al. 2010; Loewith
2010; Soulard et al. 2010) also suggest that TORC1 plays an
active role in mRNA stability and, via its potential substrate
Sky1, in pre-mRNA splicing. This observation is significant
when one considers that 90% of all mRNA splicing events
occur on RP transcripts (Warner 1999). Thus, TORC1 is well
positioned to coordinate multiple aspects of ribosome biogen-
esis in response to growth stimuli. As introduced above,
TORC1 activity is dramatically increased in sfp1 and sch9 cells
(Lempiainen et al. 2009), suggesting that some aspect of ribo-
some biogenesis must also signal in a feedback loop to TORC1.
It will be interesting to see what steps of ribosome biogenesis
contribute to TORC1 regulation.
Regulation of cell cycle/cell size: Although distinct pro-
cesses, cell growth and cell division are often intimately
linked. Yeast cells, for example, commit to a new round of
cell division only after attaining a critical size. This cell-size
threshold is dictated in large part by environmental growth
conditions (Cook and Tyers 2007). How cells couple envi-
ronmental cues to the cell cycle machinery is fascinating but
poorly understood. Interestingly, sfp1 and sch9 were the top
two hits in a systematic search for mutations conferring
small cell size (Jorgensen et al. 2002, 2004). This and fol-
low-up observations demonstrated that ribosome biogenesis
plays a major role in cell-size determination. These results
further predict that environmental cues regulate the cell-size
threshold via TORC1, i.e., that poor growth conditions re-
duce the activity of TORC1 and subsequently the activities of
Sfp1 and Sch9. Consequently, this would decrease ribosome
biogenesis, which, in mysterious ways, would lower the cell-
size threshold required for cell division. In contrast, acute
inhibition of TORC1 with high concentrations of rapamycin
leads to an arrest in G1 due to reduced translation of the
cyclin Cln3 (Barbet et al. 1996) and a paradoxical increase
in cell size. This increase in cell size is actually due to swell-
ing of the vacuole as a consequence of increased autophagy
(see below; sfp1 or sch9 deletions presumably do not induce
Although best appreciated for its role in G1 regulation,
TORC1 additionally regulates the transition through other
phases of the cell cycle. TORC1 promotes S phase by
maintaining deoxynucleoside triphosphate pools. Deoxy-
nucleoside triphosphates are the obligate building blocks
for DNA synthesis, and a role for TORC1 in their synthesis
becomes apparent under conditions of DNA replication
stress or DNA damage when elevated deoxynucleoside
triphosphate pools are necessary for error-prone trans-
lesion DNA polymerases (Shen et al. 2007). Via the Tap42-
PPase branch, TORC1 also influences the G2/M transition
(Nakashima et al. 2008). Specifically, TORC1 regulates the
subcellular localization of the polo-like kinase Cdc5. Cdc5
activity destabilizes Swe1, a kinase that phosphorylates and
thus inactivates the mitotic cyclin-dependent kinase Cdc28.
Inhibition of TORC1 mislocalizes Cdc5, causing an inappro-
priate stabilization of Swe1 and, consequently, inactivation
of Cdc28 and prolonged G2/M. Although TORC1 signals
likely impinge upon additional nodes in the cell division
cycle (Huber et al. 2009; Soulard et al. 2010), the above
R. Loewith and M. N. Hall
observations already exemplify the intricate connections be-
tween cell growth signals and the cell division cycle. Recip-
rocal, but less well described, cues and/or outputs from the
cell division cycle regulate cell growth, likely in part via
TORC1 (Goranov and Amon 2010).
TORC1 inhibits stress responses: In addition to stimulating
anabolic processes, TORC1 also promotes growth by sup-
pressing a variety of stress-response programs. Although
essential for surviving environmental insults, activation of
stress-responsive pathways is incompatible with rapid
growth, and constitutive activation of these pathways
generally results in cell death. As described below, the
best-characterized stress-response programs under the in-
fluence of TORC1 are transcriptional in nature. However, it
is clear that TORC1 also regulates post-transcriptional
aspects of stress responses such as mRNA stability, protein
trafficking, and the activities of metabolic enzymes.
Environmental stress response: Exposure of yeast cells to
noxious stressors, including nutrient limitation and entry
into stationary phase, elicits a stereotypic transcriptional
response known as the environmental stress response
(ESR) (Gasch and Werner-Washburne 2002). This includes
?300 upregulated genes that encode activities such as pro-
tein chaperones and oxygen radical scavengers that help
cells endure stressful environments. The central compo-
nents of this pathway are the Zn-finger transcription fac-
tors Msn2/4 and Gis1, the LATS family kinase Rim15, and
the a-endosulfine family paralogs Igo1 and Igo2 (De Virgilio
2011). TORC1 via Sch9, and possibly also Tap42-PPase,
promotes cytoplasmic anchoring of Rim15 to 14-3-3 pro-
teins by maintaining Rim15 phosphorylated on Ser1061
and Thr1075 (Wanke et al. 2005, 2008). Inhibition of
TORC1 results in nuclear localization of Rim15, which sub-
sequently triggers the activation, in a poorly understood
fashion, of the expression of Msn2/4- and Gis1-dependent
ESR genes. However, TORC1 inhibition results in a marked
turnover of mRNAs (Albig and Decker 2001), and, as noted
above, in a dramatic drop in translation. Thus it would
appear that increasing transcription of protein-coding genes
in TORC1-inhibited cells would be futile as these mRNA
would likely be degraded before ever being translated. This
appears not to be the case as Rim15 phosphorylates Igo1
and its paralog Igo2, allowing them to associate with newly
transcribed Msn2/4- and Gis1-regulated mRNAs to protect
these transcripts from degradation via the 59-39 mRNA
decay pathway (Talarek et al. 2010; Luo et al. 2011).
Nutrient uptake and intermediary metabolism: To best
compete with other microbes in their environment, yeast
have optimized the use of available nutrients to accommo-
date fast growth (De Virgilio and Loewith 2006). Although
a wide variety of compounds can be utilized as carbon or
nitrogen sources, yeast cells will exclusively assimilate pre-
ferred nutrient sources before using nonpreferred, subopti-
mal ones. To attain this dietary specificity, and to respond to
nutritional stress, yeast cells carefully regulate the expres-
sion and sorting of their many (.270) membrane transport-
ers, enabling them to selectively import only the desired
nutrients (Van Belle and Andre 2001). In general terms,
in good growth conditions, many high-affinity, substrate-
selective permeases are expressed and sorted to the plasma
membrane to actively pump in nutrients that are used
directly in ATP production and/or anabolism of nitrogenous
compounds. Shift to poor growth conditions results in the
replacement of high-affinity permeases, which are targeted
to the vacuole for degradation with few low-affinity, broad-
specificity permeases that facilitate uptake of a wide range
of carbon and nitrogenous compounds that can be catabo-
lized by the cell. For example, in response to nitrogen star-
vation, the high-affinity tryptophan-specific permease, Tat2,
localized to the plasma membrane, is ubiquitinated, endo-
cytosed, and ultimately degraded. In contrast, the general
amino acid permease Gap1 is re-routed to the plasma mem-
brane instead of to the vacuole/endosomes. Although
details are still emerging, TORC1 appears to regulate such
permease-sorting events primarily via Tap42-PPase and
its (potentially direct) effector Npr1 (Schmidt et al. 1998;
Beck et al. 1999; De Craene et al. 2001; Jacinto et al. 2001;
Soetens et al. 2001; Breitkreutz et al. 2010). Npr1 is a heavily
phosphorylated, seemingly fungal-specific, Ser/Thr kinase
that upon TORC1 inactivation is rapidly dephosphorylated
and activated (Gander et al. 2008). Although genetic studies
clearly imply a role for Npr1 in protein-sorting events, the
mechanisms of this regulation have remained elusive. It is
possible that the permeases themselves are Npr1 substrates.
Indeed, several nutrient and cation permeases have been
identified as rapamycin-sensitive phosphoproteins (Huber
et al. 2009; Soulard et al. 2010). Also identified in these
phosphoproteomics studies were several a-arrestin-related
proteins. These phosphoproteins function as clathrin adap-
tor molecules and have been implicated in mediating the
sorting fates of a number of different permeases; and, one,
Aly2, has recently been reported to be an Npr1 substrate
(Lin et al. 2008; Nikko et al. 2008; Nikko and Pelham
2009; O’Donnell et al. 2010). Whether this observation is
indicative of a more general trend in Npr1-meditated per-
mease trafficking remains to be seen.
TORC1 regulates permease activity by regulating not only
permease localization but also expression. This was shown in
early transcriptomics experiments, which clearly demon-
strated that TORC1 regulates the expression of a large
number of permeases and other factors required for the
assimilation of alternative nitrogenous sources (Cardenas
et al. 1999; Hardwick et al. 1999; Komeili et al. 2000; Shamji
et al. 2000). TORC1 regulates the expression of nitrogen
catabolite repression (NCR)-sensitive genes via the Tap42-
PPase branch. The proteins encoded by these genes (e.g.,
Gap1) enable cells to import and metabolize poor nitrogen
sources such as proline and allantoin. In the presence of
preferred nitrogen sourcessuch as glutamine, glutamate, or am-
monia, active TORC1 promotes the association of the GATA-
family transcription factor Gln3 with its cytoplasmic anchor
Ure2. Mechanistically, this involves both TORC1-dependent
and TORC1-independent regulation of Gln3, and possibly of
Ure2, phosphorylation (Beck and Hall 1999; Cardenas et al.
1999; Hardwick et al. 1999; Carvalho and Zheng 2003;
Georis et al. 2009a; Tate et al. 2009, 2010). Two other
less-characterized GATA factors, Gat1 and Dal81, also have
roles in the regulation of NCR-sensitive genes (Georis et al.
In addition to the NCR pathway, TORC1 also regulates
the expression of amino acid permeases by modulating the
activity of the SPS-sensing pathway. This pathway consists of
a plasma-membrane-localized sensor of external amino
acids, Ssy1, and two downstream factors, Ptr3 and Ssy5
(Ljungdahl 2009). Upon activation of the pathway, Ssy5
catalyzes an endoproteolytic processing event that cleaves
and releases an N-terminal regulatory domain from two
transcription factors, Stp1 and Stp2, the shortened forms
of which translocate to the nucleus and activate the tran-
scription of a number of amino acid permease-encoding
genes. TORC1 via Tap42-PPase modulates this pathway by
promoting the stability of Stp1 and thus the ability of cells to
utilize external amino acids (Shin et al. 2009).
In contrast to the SPS-sensing pathway that is activated
by amino acids, the Gcn4 transcription factor is activated
upon amino acid starvation (Hinnebusch 2005). As men-
tioned above, rapamycin treatment or amino acid starvation
results in a rapid decline in translation initiation by trigger-
ing phosphorylation of the a-subunit of eIF2. Although
eIF2a phosphorylation results in the repression of bulk
translation, due to the presence of four short upstream open
reading frames in its leader sequence, the mRNA encoding
Gcn4 is, in contrast, preferentially translated. Subsequent
accumulation of Gcn4 protein leads to the transcriptional
induction of nearly all genes encoding amino acid biosyn-
TORC1 also regulates amino acid biosynthesis, in partic-
ular glutamine and glutamate homeostasis, via the retro-
grade response pathway (Komeili et al. 2000; Crespo and
Hall 2002; Crespo et al. 2002; Liu and Butow 2006). This
signaling pathway serves to communicate mitochondrial
dysfunction to the nucleus to induce an appropriate tran-
scriptional response. In addition to hosting the aerobic en-
ergy production machinery, mitochondria are also the sites
of amino acid precursor, nucleotide, and lipid production.
Signals, possibly changes in glutamate or glutamine levels,
emanating from dysfunctional mitochondria impinge upon
a cytosolic regulatory protein, Rtg2. Thus activated, Rtg2
antagonizes the ability of Mks1 to sequester the heterodi-
meric bZip/HLH transcription factor complex composed of
Rtg1 and Rtg3 in the cytoplasm. Allowed to enter the nu-
cleus, Rtg1/3 activates genes encoding enzymes required for
anaplerotic reactions that resupply tri-carboxylic acid cycle
intermediates that have been extracted for biosynthetic
reactions. Key among these intermediates is a-ketoglutarate,
the precursor of glutamate and glutamine from which
all nitrogen-containing metabolites evolve (Magasanik and
Kaiser 2002). Both transcriptome-profiling experiments as
well as genetic studies have implicated TORC1 as a negative
regulator of Rtg1/3-dependent transcription (Komeili et al.
2000; Shamji et al. 2000; Chen and Kaiser 2003). However,
it is presently unclear how TORC1 influences this pathway;
TORC1 inhibition could indirectly influence retrograde re-
sponse signaling via alterations in metabolite levels. Alter-
natively, the direct association between TORC1 and Mks1
observed by the Tyers group and described above and the
fact that Mks1 is a rapamycin-sensitive phosphoprotein in-
stead suggest that TORC1 could play a much more direct
role in regulating this pathway (Liu et al. 2003; Breitkreutz
et al. 2010). Finally, phosphoproteomics studies suggest that
TORC1 regulates intermediate metabolism by directly alter-
ing the activities of metabolic enzymes, particularly those
involved in the early steps of glycolysis (Loewith 2011).
Autophagy: As described above, starved cells express
a suite of stress-responsive proteins to help them negotiate
hostile environmental conditions.
requires both energy and amino acids that yeast cells obtain
by inducing autophagy. Autophagy refers to a variety of
mechanisms by which cytosplasmic material, including
proteins and lipids, is translocated to the vacuole and
catabolized. Amino acids and fatty acids thus acquired are,
respectively, used to synthesize new proteins and oxidized
by mitochondria to produce ATP. Mechanistically, there are
two different modes of autophagy in yeast. One is micro-
autophagy, which involves the direct transfer of cytoplasm
into the vacuole via invaginations of the vacuolar mem-
brane. The other is macroautophagy, which involves the de
novo formation of double-membrane vesicles called auto-
phagosomes. Autophagosomes encapsulate cytoplasm and
then fuse with the vacuole. Both forms of autophagy are
regulated by TORC1 (De Virgilio and Loewith 2006)
although, mechanistically, macroautophagy is better under-
stood (reviewed in Cebollero and Reggiori 2009; Nakatogawa
et al. 2009; Inoue and Klionsky 2010).
Autophagy is conserved across eukarya, and there is
much interest in understanding how macroautophagy is
regulated as it has been linked to several pathologies
including cancer, neurological disorders, and longevity
(Yang and Klionsky 2010). In yeast, many autophagy-
related (ATG) genes encode proteins that participate in the
induction of autophagy, the nucleation of the autophagosome,
elongation and completion of the autophagosome, and,
finally, in fusion of the autophagosome with the vacuole to
release the autolysosome into the vacuolar lumen (Chen and
Klionsky 2011; Reiter et al. 2011). TORC1 regulates macro-
autophagy by signaling to the Atg1 kinase complex that is
required for the induction of macroautophagy. Specifically,
when TORC1 is active, Atg13 is hyperphosphorylated, pre-
sumably directly by TORC1 (although Tap42-PPase has also
been implicated in this regulation), and this prevents the
association of Atg13 with Atg1, Atg17, Atg31, and Atg29
(Yorimitsu et al. 2009; Kamada et al. 2010). Inhibition of
TORC1 results in dephosphorylation of Atg13, assembly
of the Atg1 protein kinase complex, phosphorylation and
This new synthesis
R. Loewith and M. N. Hall
activation of Atg1 (Kijanska et al. 2010; Yeh et al. 2010), and,
subsequently, macroautophagy mediated by as-yet-unidenti-
fied Atg1 substrates. Although metazoan homologs exist for
many of the Atg1 kinase complex components, a unifying
model of how TORC1 regulates this complex in different spe-
cies has yet to emerge (Chen and Klionsky 2011; Reiter et al.
Cell-wall integrity pathway: The cell wall is essential for
yeast cells to survive hostile environments and, more
importantly, to prevent internal turgor pressure from rup-
turing the plasma membrane. Although a thickening of the
cell wall helps protect stressed or stationary-phase cells, this
rigid structure must also be remodelled to accommodate cell
growth. Homeostasis of this structure is maintained by the
cell-wall integrity (CWI) pathway (Levin 2005). Cell-wall
integrity is monitored by WSC (cell-wall integrity and stress
response component) family proteins. WSCs, which are in-
tegral plasma membrane proteins, function upstream of the
Rho1 GTPase by modulating the activity of the GEFs Rom1
and Rom2. Rho1GTPhas several effectors including the yeast
protein kinase C homolog, Pkc1. The best-characterized
Pkc1 effector is a mitogen-activated protein kinase (MAPK)
cascade composed of Bck1 (a MAPKKK), Mkk1 and -2
(redundant MAPKKs), and Slt2/Mpk1 (a MAPK). Activation
of this pathway leads to the expression of many cell-wall
biosynthetic enzymes, which helps to remodel the cell wall
both during normal growth and in response to stress.
Both TORC1 and TORC2 (discussed below) appear to
impinge upon the CWI pathway. Entry into stationary phase,
carbon starvation, nitrogen starvation, and rapamycin treat-
ment all elicit activation of the CWI pathway, demonstrating
that TORC1 negatively regulates the CWI pathway (Ai et al.
2002; Krause and Gray 2002; Torres et al. 2002; Reinke
et al. 2004; Araki et al. 2005; Soulard et al. 2010). Further-
more, pkc1, bck1, and mpk1 mutants rapidly lose viability
upon carbon or nitrogen starvation, demonstrating that the
CWI pathway is required for viability in G0. Mechanistically,
how TORC1 signals impinge on the CWI pathway is not
clear. Soulard et al. (2010) have implicated the Sch9 effector
branch while Torres et al. (2002) have postulated that sig-
nals through the Tap42-PPase branch causes membrane
stress that, via WSC family members, activates downstream
components of the CWI pathway.
TORC1 accelerates aging: Arguably one of the most
interesting functions of TORC1 is its involvement in the
regulation of life span. It is well established that, in virtually
every biological system, aging, i.e., the progressive deterio-
ration of cell, tissue, and organ function, can be delayed
through calorie or dietary restriction. Epistasis studies have
led many to believe that this is due to reduced TORC1
signaling (reviewed in Weindruch and Walford 1988;
Kapahi et al. 2010; Zoncu et al. 2010, 2011; Kaeberlein
and Kennedy 2011). Indeed, genetic or chemical targeting
of TORC1 has been demonstrated to increase life span in
yeast, worms, flies, and mice (Vellai et al. 2003; Jia et al.
2004; Kapahi et al. 2004; Wanke et al. 2008; Harrison et al.
2009; Bjedov et al. 2010). These observations have created
much excitement in that aging is now thought of as a dis-
ease, which, like other diseases, can be ameliorated through
pharmaceutical intervention. These observations have also
raised the important question, what are the downstream
function(s) of TORC1 that modulate life span? The answer
to this question is presently unclear, and it is very likely that
multiple TORC1 effector pathways contribute (Blagosklonny
and Hall 2009). Studies in many model systems are pres-
ently underway to address this issue. Below are some of the
highlights from studies in yeast.
Yeast life span is assayed in one of two ways. Replicative
life span (RLS) is a measure of the number of progeny that
a single mother cell can produce before senescence. Chro-
nological life span (CLS) is a measure of the length of time
a population of yeast cells can remain in stationary phase
before they lose the ability to restart growth following re-
inoculation into fresh media. RLS is thought to be a para-
digm for aging of mitotic cells while CLS is thought to be
a paradigm for aging of quiescent cells. Consistent with
bigger eukaryotes, where newborns are obviously born
young, gametogenesis (i.e., cells derived from meiotic cell
divisions) resets RLS in yeast (Unal et al. 2011).
Kaeberlein et al. (2005) have recently attempted labor-
intensive approaches to identify genes involved in both rep-
licative and chronological life span. A random screen of 564
yeast strains, each lacking a single nonessential gene, impli-
cated both TOR1 and SCH9 in RLS downstream of caloric
restriction. Also identified in this screen were a number of
genes encoding ribosomal proteins. Further analyses of RP
genes subsequently demonstrated that specific depletion of
60S ribosomal protein subunits extends RLS (Steffen et al.
2008). Curiously, RLS extension observed upon TORC1 inhi-
bition and 60S subunit depletion seems to be mediated by
Gcn4, the TORC1-dependent transcription factor that regu-
lates the expression of amino acid biosynthetic genes as de-
scribed above. The relevant Gcn4 target genes/processes
involved in RLS are not yet known, but an interesting candi-
date could be macroautophagy. Induction of macroautophagy,
like TORC1 and Sch9 inhibition, increases both RLS and CLS
(Madeo et al. 2010a,b; Morselli et al. 2011; and see below),
and Gcn4 is required for amino acid-starvation-induced mac-
roautophagy (Ecker et al. 2010). Furthermore, spermidine,
a potent inducer of macroautophagy, potentially via Gcn4
(Teixeira et al. 2010), appears to promote longevity not only
in yeast but also in several other model organisms (Eisenberg
et al. 2009). Since TORC1, Sch9, and Gcn4 homologs are
found in most eukaryotes, this appears to represent a con-
served aging pathway (Kaeberlein and Kennedy 2011).
Sch9 was one of the first genes to be implicated in CLS
(Fabrizio et al. 2001). A subsequent high-throughput assay
involving 4800 viable single-gene yeast mutants further impli-
cated TORC1 in CLS (Powers et al. 2006). These and other
studies (Wanke et al. 2008; Wei et al. 2008) provided evidence
that reduced TORC1-Sch9-signaling activity promotes life span
byincreasingthe Rim15-dependent expressionofenvironmental
stress-response genes (described above). Later, Burtner et al.
(2009) demonstrated that acetic acid-induced mortality is the
primary mechanism of chronological aging in yeast under stan-
dard conditions and that this toxicity is better tolerated when
environmental stress-response genes are artificially induced,
for example, upon inhibition of TORC1 or Sch9 activities. How-
ever, this model is not universally accepted. Pan et al. (2011)
have proposed that TORC1 inhibition leads to increased mito-
chondrial function and a consequent increase in reactive oxy-
gen species that elicit a Rim15-independent pro-survival signal.
Furthermore, acetic acid accumulation appears not to be a con-
tributing factor in CLS in this study. Given its apparent conser-
vation acrosseukarya (Blagosklonny
elucidation of the mechanisms by which TORC1 regulates life
span is eagerly awaited.
Less-characterized effectors identified in phosphoproteomic
studies: As alluded to above, large-scale mass spectrometry-
based phosphoproteomic studies have recently been per-
formed to identify the rapamycin-sensitive phosphoproteome
(Huber et al. 2009; Soulard et al. 2010). The major limitation
of these studies was their poor coverage as evidenced by their
rather modest overlap, although this could be partly explained
by the different growth conditions and technical approaches
employed. Rapamycin exposure times were chosen such that
layers of signaling events (e.g., kinase/phosphatase cascades)
would be observed. These events should have been triggered
as a direct consequence of TORC1 inhibition and not as a sec-
ondary consequence of cell cycle delays or changes in tran-
scription. Hundreds of rapamycin-sensitive phosphorylation
sites were mapped, the majority of which are in proteins
not previously implicated in TORC1 signaling. However, as
sufficient time elapsed to activate entire signaling cascades,
a potential TORC1 consensus target motif was not evident
from the data analyses. Still, the data from these studies
will be instrumental in both elucidating how TORC1 signals
to its known distal readouts and discovering new TORC1
TOR Complex 2
Composition and localization of TOR complex 2
TOR complex 2 (TORC2) is rapamycin insensitive and
consists of TOR2, Avo1, Avo2, Avo3, Bit61 (and/or its
paralog Bit2), and Lst8 (Loewith et al. 2002; Wedaman
et al. 2003; Reinke et al. 2004; Zinzalla et al. 2010) (Figure
1C). The names of mammalian and invertebrate orthologs of
TORC2 subunits and the salient features of S. cerevisiae
TORC2 subunits are summarized in Table 1 and Table 4,
respectively. The highly conserved, essential core subunits
are TOR2, Avo1, Avo3, and Lst8. Avo1 and Avo3 bind co-
operatively to the N-terminal HEAT repeat region in TOR2
and are required for TORC2 integrity (Wullschleger et al.
2005). TORC2 autophosphorylates sites in Avo1 and Avo3,
but the purpose of this phosphorylation is unknown. Avo1
has a C-terminal PH-like domain that mediates binding
to the plasma membrane (Berchtold and Walther 2009).
Avo3 has a RasGEFN domain, a subdomain often found in
the N-terminal part of a larger GDP/GTP exchange domain
of exchange factors for Ras-like GTPases, but the function of
the RasGEFN domain is unknown. Lst8 binds to the kinase
domain in TOR2 and is required for TOR2 kinase activity
(Wullschleger et al. 2005). Lst8 is a Gb-like propeller pro-
tein consisting of seven WD40 motifs. TORC2 is rapamycin
insensitive whereas TORC1 is rapamycin sensitive because
FKBP-rapamycin binds only TORC1 (Loewith et al. 2002).
This selective FKBP-rapamycin binding is presumably due to
Avo1 masking the FRB domain in TOR2 in TORC2. Finally,
co-immunoprecipitation and gel filtration experiments sug-
gest that TORC2 is a multimer, likely a TORC2-TORC2 di-
mer (Wullschleger et al. 2005).
The cellular localization of TORC2 has been studied by
immunogold electron microscopy, and visualization of GFP-
tagged TORC2 components (Kunz et al. 2000; Wedaman
et al. 2003; Aronova et al. 2007; Sturgill et al. 2008; Berchtold
and Walther 2009). In considering these studies, it is impor-
tant to realize that the vast majority of TOR2 (?90%) is in
TORC2 (vs. TORC1), and thus TOR2 localization studies pre-
sumably detect mainly, if not exclusively, TORC2. All studies
indicate that TORC2 is at or near the plasma membrane.
Berchtold and Walther (2009) suggest that TORC2 is dynam-
ically localized to a previously unrecognized plasma mem-
brane domain termed the MCT (membrane compartment
containing TORC2). Furthermore, they conclude that TORC2
plasma membrane localization is essential for viability and is
mediated by the C-terminal PH domain in Avo1. Most of the
localization studies have found that TORC2 is also at another,
ill-defined cellular location(s). For example, Kunz et al.
Table 4 Salient features of TORC2 components
Protein SizeMotifs/domainsPotential function
Tor22470 aa HEAT repeats, FAT domain, FRB domain,
kinase domain, and FATC domain
7 WD-40 repeats
Protein kinase, scaffold
Recruit TORC2 to plasma membrane
Paralogs with unknown function
Paralogs with unknown function
Stabilize kinase domain
Data for this table were obtained from Cybulski and Hall (2009).
R. Loewith and M. N. Hall
(2000) report that part of TOR2 is also in an unknown sub-
cellular membrane fraction distinct from Golgi, vacuoles,
mitochondria, and the nucleus. Wedaman et al. (2003)
showed that TOR2 can be in the cell interior often in asso-
ciation with membrane tracks. Sturgill et al. (2008) detected
a cytoplasmic fluorescent signal in cells expressing GFP-
tagged TOR2. In conclusion, TORC2 appears to be at mul-
tiple cellular locations, the plasma membrane, and one or
possibly more other sites. A plasma membrane location is
consistent with the role of TORC2 in controlling the actin
cytoskeleton and endocytosis (see below).
Upstream of TORC2
The upstream regulation of TORC2 is poorly characterized
(Cybulski and Hall 2009). Several lines of evidence in many
different organisms indicate that nutrients regulate TORC1
(see above). On the other hand, there is no reported evidence
supporting the notion that TORC2 is controlled by nutrients.
Knockout of TORC2 does not confer a starvation-like pheno-
type, and the nutrient-sensitive EGO complex appears not to
be upstream of TORC2. Zinzalla et al. (2011) recently devised
a “reverse” suppressor screen to identify upstream regulators
of TORC2. This screen was based on the observation that
constitutively active Ypk2 (Ypk2*) suppresses the loss of via-
bility due to a TORC2 defect. Ypk2 is a protein kinase nor-
mally phosphorylated and activated by TORC2 (see below).
Zinzalla et al. (2011) screened for mutants that require Ypk2*
for viability. As predicted, this screen isolated several mutants
defective in genes encoding essential TORC2 components,
but also in the gene NIP7. Subsequent experiments confirmed
that Nip7, a ribosome maturation factor, is required for
TORC2 kinase activity. The role of Nip7 in the activation of
yeast TORC2 has so far not been pursued further, but experi-
ments in mammalian cells suggest that mNip7 is required for
mTORC2 activation indirectly via its role in ribosome matu-
ration. In mammalian cells, and presumably also in yeast
cells, TORC2 is activated by direct association with the ribo-
some. As ribosomes determine the growth capacity of a cell,
this mechanism ensures that TORC2 is active only in growing
There are also indications that environmental stress
inhibits TORC2 signaling, possibly to prevent growth in
unfavorable conditions. The mechanism of this regulation
and the level at which it intersects with the TORC2 pathway
are poorly defined, but it may involve the Slm proteins (see
below) and the stress-activated phosphatase calcineurin
(Bultynck et al. 2006; Mulet et al. 2006).
The best-characterized and possibly the major TORC2 sub-
strate is the protein kinase Ypk. Ypk1 and Ypk2 are an es-
sential pair of homologous kinases and members of the AGC
kinase family (Roelants et al. 2004) (Figure 4). Kamada
et al. (2005) linked Ypk to TORC2 signaling upon isolating
YPK2 as a multicopy suppressor of a TORC2 defect. They
then showed that immunopurified TOR2 directly phosphor-
ylates Ypk2 at Ser641 in the turn motif and Thr659 in the
hydrophobic motif. TORC2 phosphorylates and activates
Gad8 and SGK1, the S. pombe and mammalian orthologs
of Ypk, respectively, in a similar manner (Matsuo et al.
2003; Garcia-Martinez and Alessi 2008). It is well estab-
lished that TORC1 or TORC2 phosphorylates the turn and
hydrophobic motifs in several kinases as a conserved mech-
anism of activation of AGC kinase family members (see
above) (Jacinto and Lorberg 2008). Ypk/Gad8/SGK1
appears to be a major TORC2 substrate as an ypk, gad8, or
sgk1 mutation phenocopies a TORC2 defect, and overex-
pression of Ypk2, Gad8, or SGK1 is sufficient to suppress
a TORC2 defect in S. cerevisiae, S. pombe, or Caenorhabditis
elegans, respectively (Matsuo et al. 2003; Kamada et al.
2005; Jones et al. 2009; Soukas et al. 2009). The two ho-
mologous, TORC2- and phosphoinositide (PI4,5P2)-binding
proteins Slm1 and Slm2 have also been reported to be phos-
phorylated in a TORC2-dependent manner both in vivo and
in vitro (Audhya et al. 2004; Fadri et al. 2005). However, the
physiological relevance of Slm phosphorylation is unknown
other than that it appears to be required for localization of
Slm to the plasma membrane (Audhya et al. 2004; Fadri
et al. 2005).
Distal readouts downstream of TORC2
The first described and best-characterized TORC2 readout is
the actin cytoskeleton (Figure 4). TORC2 controls the cell
cycle-dependent polarization of the actin cytoskeleton. As
the polarized actin cytoskeleton directs the secretory path-
way and thereby newly made protein and lipid to the grow-
ing daughter bud, this is a mechanism by which TORC2
mediates spatial control of cell growth. The first indication
that TOR2 is linked to the actin cytoskeleton came from the
isolation of TCP20, which encodes an actin-specific chaper-
one, as a dosage suppressor of a dominant-negative TOR2
“kinase-dead” mutation (Schmidt et al. 1996). This, in turn,
led to the discovery that tor2 mutants display an actin
Figure 4 Signaling by TORC2. TORC2 directly phosphorylates the AGC
kinase family member Ypk (Ypk1 and 2) and the PH domain containing
protein Slm (Slm1 and -2). Downstream effectors include the phospha-
tase calcineurin, the transcription factor Crz1, and Pkc1. TORC2 controls
organization of the actin cytoskeleton, endocytosis, sphingolipid biosyn-
thesis, and stress-related transcription. The effector pathways by which
TORC2 controls these processes are incompletely understood (see Distal
readouts downstream of TORC2 for further details).
organization defect (Schmidt et al. 1996). The subsequent
isolation of sac7, which encodes a Rho-GAP (GTPase-
activating protein), as a second-site suppressor of a tor2-
temperature-sensitive (ts) mutation suggested that TOR2
is linked to the actin cytoskeleton via a signaling pathway
containing a Rho GTPase. It was later demonstrated that
Sac7 is indeed a GAP for Rho1 and that TOR2 activates
the Rho1 GTPase switch via the Rho1-GEF Rom2 (Schmidt
et al. 1997; Bickle et al. 1998). Rom2 GEF activity is reduced
in extracts from a tor2-ts mutant (Schmidt et al. 1997; Bickle
et al. 1998). The finding that overexpression of Rom2 sup-
presses a tor2-ts mutation, whereas overexpression of cata-
lytically active Rom2 lacking its lipid-binding PH domain
does not suppress, suggested that TOR2 signals to Rom2
via the PH domain. It was subsequently shown that TOR2
signals to the actin cytoskeleton mainly, if not exclusively,
via the Rho1 effector Pkc1 (protein kinase C) and the Pkc1-
controlled cell-wall integrity MAP kinase cascade (Helliwell
et al. 1998b).
How might TORC2 signal to Rom2 to activate the Rho1
GTPase switch? The PH domain in Rom2 suggests that it
may involve a lipid intermediate. This possibility is sup-
ported by the observation that overexpression of the PI-4-
P 5-kinase Mss4 suppresses a tor2-ts mutation (Desrivieres
et al. 1998; Helliwell et al. 1998a) and that PI4,5P2at the
plasma membrane is required to recruit/activate Rom2
(Audhya and Emr 2002). The mechanism by which TORC2
may activate PI4,5P2signaling or possibly a parallel path-
way converging on the cell-wall integrity pathway is un-
known, but likely involves the well-established TORC2
substrate Ypk (Roelants et al. 2002; Schmelzle et al.
2002; Kamada et al. 2005; Mulet et al. 2006). The phos-
phoinositide-binding Slm proteins and sphingolipids may
also be functionally related to TORC2-mediated control
of the actin cytoskeleton (Sun et al. 2000; Friant et al.
2001; Roelants et al. 2002; Audhya et al. 2004; Fadri
et al. 2005; Liu et al. 2005; Tabuchi et al. 2006; Daquinag
et al. 2007).
A second downstream process controlled by TORC2 is
endocytosis. Efficient internalization of cell-surface compo-
nents is an important aspect of cell growth control. deHart
et al. (2003) identified a tor2 mutation in a screen for
mutants defective in ligand-stimulated internalization of
a cell-surface receptor. TORC2 appears to control endocyto-
sis via Rho1, Ypk1, and possibly the Slm proteins, but how
Rho1, Ypk1, and the Slm proteins are functionally related in
(deHart et al. 2002, 2003; Bultynck et al. 2006).
A third TORC2-regulated process is sphingolipid biosyn-
thesis (Powers et al. 2010). Sphingolipids serve as essential
structural components in lipid bilayers and as signaling mol-
ecules. The first indication that TORC2 controls sphingolipid
synthesis was the finding that overexpression of SUR1 sup-
presses a temperature-sensitive tor2 mutation (Helliwell et al.
1998a). In a parallel study, Beeler et al. (1998) reported that
a mutation in TOR2 or AVO3 (also known as TSC11), or
endocytosis is unknown
mutations in genes encoding components of the sphingolipid
biosynthetic pathway, suppress a csg2 mutation. Sur1/Csg1
and Csg2 are subunits, probably the catalytic and regulatory
subunits, respectively, of mannosylinositol phosphorylcera-
mide synthase that mediates a late step in sphingolipid bio-
synthesis. The Slm proteins were subsequently also linked to
sphingolipid metabolism (Tabuchi et al. 2006; Daquinag et al.
2007). Most recently, Aronova et al. (2008) profiled sphingo-
lipids in a conditional avo3 mutant and thereby confirmed
that TORC2 plays a positive role in sphingolipid biosynthesis.
Aronova et al. (2008) also investigated the molecular mech-
anism by which TORC2 controls sphingolipids. They found
that TORC2 regulates sphingolipid production via Ypk2 and
suggest a model wherein TORC2 signaling is coupled to
sphingoid long-chain bases (early intermediates in sphingoli-
pid synthesis) to control Ypk2 and late steps in sphingolipid
synthesis. Furthermore, the biosynthetic step controlled
by TORC2 and Ypk2 is antagonized by the phosphatase cal-
cineurin that is functionally linked to the Slm proteins
(Bultynck et al. 2006; Mulet et al. 2006; Aronova et al.
2008). Another potential target for the regulation of sphingo-
lipid biosynthesis by TOR are the Orm1 and Orm2 proteins.
The conserved Orm proteins, identified as a potential risk
factor for childhood asthma, form a complex that negatively
regulates the first and rate-limiting step in sphingolipid bio-
synthesis (Breslow et al. 2010; Han et al. 2010). Both Orm1
and Orm2 are phosphoproteins and at least Orm1 phosphor-
ylation changes upon rapamycin treatment (Huber et al.
2009; Soulard et al. 2010). Furthermore, loss of Orm2 sup-
presses a Ypk deficiency (Roelants et al. 2002; Schmelzle et al.
2002; Kamada et al. 2005; Mulet et al. 2006). These findings
suggest that both TORC1 and TORC2 may control sphingoli-
pid synthesis via Orm proteins.
What is upstream of the two complexes?
How TORC activities are altered in response to environ-
mental cues remains a major void in our understanding of
the TOR-signaling network. The TOR complexes are regu-
lated by nutrients, stress, or ribosomes, but the mechanisms
by which these inputs are sensed and how this information
is transduced, with the notable exceptions discussed above,
to ultimately regulate kinase activity remain largely un-
known. Genetic screens, such as the reverse suppressor
screen described above, should help to further elucidate
these signaling pathways. Unlike growth factor-signaling
pathways, which are present only in metazoans, nutrient
and stress-responsive pathways are found in all eukaryotic
cells, and thus their characterization in model organisms
would have far-reaching implications.
What is downstream of the TORCs?
The TORCs play a central role in the regulation of cell
growth by signaling to a staggering number of distal
R. Loewith and M. N. Hall
downstream processes. Recent phosphoproteomics studies
have begun to illuminate the relevant phosphorylation
cascades and, in addition, have suggested the existence of
novel growth-related effectors downstream of TORC1. Sim-
ilar studies describing the TORC2-dependent phosphopro-
teome are eagerly anticipated. Elucidating these downstream
signaling events is both academically interesting and medi-
cally important; cell growth, like cell birth (division) and cell
death, is a fundamental aspect of life, and pathological or
pharmaceutical dysregulation of TOR pathways is clinically
relevant. For example, unbridled ribosome biogenesis has
been strongly implicated in cancer, and the motivation to
understand the TORC1 effectors that modulate longevity is
obvious. Thus, characterization of TOR pathways in yeast
and mammals will identify potentially druggable factors
whose targeting could yield therapeutic gain in any of
We thank Claudio De Virgilio and Michael Stahl for com-
ments on the manuscript. We acknowledge support from the
Cantons of Basel and Geneva, SystemsX.ch, the Frontiers in
Genetics and Chemical Biology National Centers for Com-
petence in Research, the European Research Council, the
Louis-Jeantet and Leenaards Foundations, and the Swiss
National Science Foundation.
Abraham, R. T., and G. J. Wiederrecht, 1996
of rapamycin. Annu. Rev. Immunol. 14: 483–510.
Adami, A., B. Garcia-Alvarez, E. Arias-Palomo, D. Barford, and O.
Llorca, 2007 Structure of TOR and its complex with KOG1.
Mol. Cell 27: 509–516.
Ai, W., P. G. Bertram, C. K. Tsang, T. F. Chan, and X. F. Zheng,
2002 Regulation of subtelomeric silencing during stress re-
sponse. Mol. Cell 10: 1295–1305.
Alarcon, C. M., J. Heitman, and M. E. Cardenas, 1999
kinase activity and identification of a toxic effector domain of
the target of rapamycin TOR proteins in yeast. Mol. Biol. Cell
Albig, A. R., and C. J. Decker, 2001
signaling pathway regulates mRNA turnover in the yeast Sac-
charomyces cerevisiae. Mol. Biol. Cell 12: 3428–3438.
Andrade, M. A., and P. Bork, 1995
ton’s disease protein. Nat. Genet. 11: 115–116.
Araki, T., Y. Uesono, T. Oguchi, and E. A. Toh, 2005
KOG1, a component of the TOR complex 1 (TORC1), is needed
for resistance to local anesthetic tetracaine and normal distribu-
tion of actin cytoskeleton in yeast. Genes Genet. Syst. 80: 325–
Aronova, S., K. Wedaman, S. Anderson, J. Yates III. and T. Powers,
2007Probing the membrane environment of the TOR kinases
reveals functional interactions between TORC1, actin, and
membrane trafficking in Saccharomyces cerevisiae. Mol. Biol.
Cell 18: 2779–2794.
Aronova, S., K. Wedaman, P. A. Aronov, K. Fontes, K. Ramos et al.,
2008Regulation of ceramide biosynthesis by TOR complex 2.
Cell Metab. 7: 148–158.
The target of rapamycin
HEAT repeats in the Hunting-
Audhya, A., and S. D. Emr, 2002
plasma membrane and functions in the Pkc1-mediated MAP
kinase cascade. Dev. Cell 2: 593–605.
Audhya, A., R. Loewith, A. B. Parsons, L. Gao, M. Tabuchi et al.,
2004 Genome-wide lethality screen identifies new PI4,5P2
effectors that regulate the actin cytoskeleton. EMBO J. 23:
Barbet, N. C., U. Schneider, S. B. Helliwell, I. Stansfield, M. F. Tuite
et al., 1996 TOR controls translation initiation and early G1
progression in yeast. Mol. Biol. Cell 7: 25–42.
Beck, T., and M. N. Hall, 1999The TOR signalling pathway con-
trols nuclear localization of nutrient-regulated transcription fac-
tors. Nature 402: 689–692.
Beck, T., A. Schmidt, and M. N. Hall, 1999
vacuolar targeting and degradation of the tryptophan permease
in yeast. J. Cell Biol. 146: 1227–1238.
Beeler, T., D. Bacikova, K. Gable, L. Hopkins, C. Johnson et al.,
1998The Saccharomyces cerevisiae TSC10/YBR265w gene
encoding 3-ketosphinganine reductase is identified in a screen
for temperature-sensitive suppressors of the Ca2+-sensitive
csg2Delta mutant. J. Biol. Chem. 273: 30688–30694.
Benjamin, D., M. Colombi, C. Moroni, and M. N. Hall, 2011
mycin passes the torch: a new generation of mTOR inhibitors.
Nat. Rev. Drug Discov. 10: 868–880.
Berchtold, D., and T. C. Walther, 2009
localization is essential for cell viability and restricted to a dis-
tinct domain. Mol. Biol. Cell 20: 1565–1575.
Berger, A. B., L. Decourty, G. Badis, U. Nehrbass, A. Jacquier et al.,
2007Hmo1 is required for TOR-dependent regulation of ribo-
somal protein gene transcription. Mol. Cell. Biol. 27: 8015–
Berset, C., H. Trachsel, and M. Altmann, 1998
rapamycin) signal transduction pathway regulates the stability
of translation initiation factor eIF4G in the yeast Saccharomyces
cerevisiae. Proc. Natl. Acad. Sci. USA 95: 4264–4269.
Bertram, P. G., J. H. Choi, J. Carvalho, W. Ai, C. Zeng et al.,
2000 Tripartite regulation of Gln3p by TOR, Ure2p, and phos-
phatases. J. Biol. Chem. 275: 35727–35733.
Beugnet, A., A. R. Tee, P. M. Taylor, and C. G. Proud,
2003 Regulation of targets of mTOR (mammalian target of
rapamycin) signalling by intracellular amino acid availability.
Biochem. J. 372: 555–566.
Bharucha, N., J. Ma, C. J. Dobry, S. K. Lawson, Z. Yang et al.,
2008Analysis of the yeast kinome reveals a network of regu-
lated protein localization during filamentous growth. Mol. Biol.
Cell 19: 2708–2717.
Bickle, M., P. A. Delley, A. Schmidt, and M. N. Hall, 1998
integrity modulates RHO1 activity via the exchange factor
ROM2. EMBO J. 17: 2235–2245.
Binda, M., M. P. Peli-Gulli, G. Bonfils, N. Panchaud, J. Urban et al.,
2009The Vam6 GEF controls TORC1 by activating the EGO
complex. Mol. Cell 35: 563–573.
Bjedov, I., J. M. Toivonen, F. Kerr, C. Slack, J. Jacobson et al.,
2010Mechanisms of life span extension by rapamycin in the
fruit fly Drosophila melanogaster. Cell Metab. 11: 35–46.
Blagosklonny, M. V., and M. N. Hall, 2009
a common molecular mechanism. Aging (Albany NY) 1: 357–
Bosotti, R., A. Isacchi, and E. L. Sonnhammer, 2000
domain in PIK-related kinases. Trends Biochem. Sci. 25: 225–
Breitkreutz, A., H. Choi, J. R. Sharom, L. Boucher, V. Neduva et al.,
2010 A global protein kinase and phosphatase interaction net-
work in yeast. Science 328: 1043–1046.
Breslow, D. K., S. R. Collins, B. Bodenmiller, R. Aebersold, K. Simons
et al., 2010Orm family proteins mediate sphingolipid homeo-
stasis. Nature 463: 1048–1053.
Stt4 PI 4-kinase localizes to the
TORC2 plasma membrane
The TOR (target of
Growth and aging:
FAT: a novel
Brown, E. J., M. W. Albers, T. B. Shin, K. Ichikawa, C. T. Keith et al.,
1994A mammalian protein targeted by G1-arresting rapamy-
cin-receptor complex. Nature 369: 756–758.
Brown, E. J., P. A. Beal, C. T. Keith, J. Chen, T. B. Shin et al.,
1995 Control of p70 s6 kinase by kinase activity of FRAP
in vivo. Nature 377: 441–446.
Bultynck, G., V. L. Heath, A. P. Majeed, J. M. Galan, R. Haguenauer-
Tsapis et al., 2006Slm1 and slm2 are novel substrates of the
calcineurin phosphatase required for heat stress-induced endo-
cytosis of the yeast uracil permease. Mol. Cell. Biol. 26: 4729–
Burtner, C. R., C. J. Murakami, B. K. Kennedy, and M. Kaeberlein,
2009A molecular mechanism of chronological aging in yeast.
Cell Cycle 8: 1256–1270.
Cafferkey, R., P. R. Young, M. M. McLaughlin, D. J. Bergsma, Y.
Koltin et al., 1993Dominant missense mutations in a novel
yeast protein related to mammalian phosphatidylinositol 3-
kinase and VPS34 abrogate rapamycin cytotoxicity. Mol. Cell.
Biol. 13: 6012–6023.
Calvert, M. E., K. M. Keck, C. Ptak, J. Shabanowitz, D. F. Hunt et al.,
2008Phosphorylation by casein kinase 2 regulates Nap1 local-
ization and function. Mol. Cell. Biol. 28: 1313–1325.
Cardenas, M. E., M. C. Cruz, M. Del Poeta, N. Chung, J. R. Perfect
et al., 1999 Antifungal activities of antineoplastic agents: Sac-
charomyces cerevisiae as a model system to study drug action.
Clin. Microbiol. Rev. 12: 583–611.
Caron, E., S. Ghosh, Y. Matsuoka, D. Ashton-Beaucage, M. Therrien
et al., 2010 A comprehensive map of the mTOR signaling net-
work. Mol. Syst. Biol. 6: 453.
Carvalho, J., and X. F. Zheng, 2003
with karyopherins, Ure2p, and the target of rapamycin protein.
J. Biol. Chem. 278: 16878–16886.
Cebollero, E., and F. Reggiori, 2009
yeast Saccharomyces cerevisiae. Biochim. Biophys. Acta 1793:
Chen, E. J., and C. A. Kaiser, 2003
amino acid biosynthesis as a component of the TOR pathway.
J. Cell Biol. 161: 333–347.
Chen, J., X. F. Zheng, E. J. Brown, and S. L. Schreiber,
1995 Identification of an 11-kDa FKBP12-rapamycin-binding
domain within the 289-kDa FKBP12-rapamycin-associated pro-
tein and characterization of a critical serine residue. Proc. Natl.
Acad. Sci. USA 92: 4947–4951.
Chen, Y., and D. J. Klionsky, 2011
unanswered questions. J. Cell Sci. 124: 161–170.
Cherkasova, V. A., and A. G. Hinnebusch, 2003
trol by TOR and TAP42 through dephosphorylation of eIF2alpha
kinase GCN2. Genes Dev. 17: 859–872.
Chiu, M. I., H. Katz, and V. Berlin, 1994
homolog of yeast Tor, interacts with the FKBP12/rapamycin
complex. Proc. Natl. Acad. Sci. USA 91: 12574–12578.
Choi, J., J. Chen, S. L. Schreiber, and J. Clardy, 1996
the FKBP12-rapamycin complex interacting with the binding
domain of human FRAP. Science 273: 239–242.
Claypool, J. A., S. L. French, K. Johzuka, K. Eliason, L. Vu et al.,
2004Tor pathway regulates Rrn3p-dependent recruitment of
yeast RNA polymerase I to the promoter but does not participate
in alteration of the number of active genes. Mol. Biol. Cell 15:
Cohen, A., and M. N. Hall, 2009
mTORC1. Cell 136: 399–400.
Cook, M., and M. Tyers, 2007 Size control goes global. Curr. Opin.
Biotechnol. 18: 341–350.
Cosentino, G. P., T. Schmelzle, A. Haghighat, S. B. Helliwell, M. N.
Hall et al., 2000 Eap1p, a novel eukaryotic translation initia-
tion factor 4E-associated protein in Saccharomyces cerevisiae.
Mol. Cell. Biol. 20: 4604–4613.
Domains of Gln3p interacting
Regulation of autophagy in
LST8 negatively regulates
The regulation of autophagy:
RAPT1, a mammalian
An amino acid shuffle activates
Crespo, J. L., and M. N. Hall, 2002
and rapamycin action: lessons from Saccharomyces cerevisiae.
Microbiol. Mol. Biol. Rev. 66: 579–591.
Crespo, J. L., T. Powers, B. Fowler, and M. N. Hall, 2002
TOR-controlled transcription activators GLN3, RTG1, and
RTG3 are regulated in response to intracellular levels of gluta-
mine. Proc. Natl. Acad. Sci. USA 99: 6784–6789.
Cybulski, N., and M. N. Hall, 2009
pathway of its own. Trends Biochem. Sci. 34: 620–627.
Dames, S. A., J. M. Mulet, K. Rathgeb-Szabo, M. N. Hall, and
S. Grzesiek, 2005 The solution structure of the FATC domain
of the protein kinase target of rapamycin suggests a role for
redox-dependent structural and cellular stability. J. Biol. Chem.
Daquinag, A., M. Fadri, S. Y. Jung, J. Qin, and J. Kunz, 2007
yeast PH domain proteins Slm1 and Slm2 are targets of sphin-
golipid signaling during the response to heat stress. Mol. Cell.
Biol. 27: 633–650.
Davis, E. S., A. Becker, J. Heitman, M. N. Hall, and M. B. Brennan,
1992A yeast cyclophilin gene essential for lactate metabolism
at high temperature. Proc. Natl. Acad. Sci. USA 89: 11169–
De Craene, J. O., O. Soetens, and B. Andre, 2001
controls biosynthetic and endocytic sorting of the yeast Gap1
permease. J. Biol. Chem. 276: 43939–43948.
deHart, A. K., J. D. Schnell, D. A. Allen, and L. Hicke, 2002
conserved Pkh-Ypk kinase cascade is required for endocytosis in
yeast. J. Cell Biol. 156: 241–248.
deHart, A. K., J. D. Schnell, D. A. Allen, J. Y. Tsai, and L. Hicke,
2003 Receptor internalization in yeast requires the Tor2-Rho1
signaling pathway. Mol. Biol. Cell 14: 4676–4684.
Desrivieres, S., F. T. Cooke, P. J. Parker, and M. N. Hall,
1998 MSS4, a phosphatidylinositol-4-phosphate 5-kinase re-
quired for organization of the actin cytoskeleton in Saccharomy-
ces cerevisiae. J. Biol. Chem. 273: 15787–15793.
De Virgilio, C., 2011 The essence of yeast quiescence. FEMS Mi-
crobiol. Rev. (in press).
De Virgilio, C., and R. Loewith, 2006
eukaryotes make big contributions. Oncogene 25: 6392–6415.
Di Como, C. J., and K. T. Arndt, 1996
proteins, stimulate the association of Tap42 with type 2A phos-
phatases. Genes Dev. 10: 1904–1916.
Dolinski, K., S. Muir, M. Cardenas, and J. Heitman, 1997
cyclophilins and FK506 binding proteins are, individually and
collectively, dispensable for viability in Saccharomyces cerevi-
siae. Proc. Natl. Acad. Sci. USA 94: 13093–13098.
Dubouloz, F., O. Deloche, V. Wanke, E. Cameroni, and C. De Virgilio,
2005 The TOR and EGO protein complexes orchestrate micro-
autophagy in yeast. Mol. Cell 19: 15–26.
Duvel, K., A. Santhanam, S. Garrett, L. Schneper, and J. R. Broach,
2003Multiple roles of Tap42 in mediating rapamycin-induced
transcriptional changes in yeast. Mol. Cell 11: 1467–1478.
Ecker, N., A. Mor, D. Journo, and H. Abeliovich, 2010
autophagic flux by amino acid deprivation is distinct from nitro-
gen starvation-induced macroautophagy. Autophagy 6: 879–
Eisenberg, T., H. Knauer, A. Schauer, S. Buttner, C. Ruckenstuhl
et al., 2009Induction of autophagy by spermidine promotes
longevity. Nat. Cell Biol. 11: 1305–1314.
Fabrizio, P., F. Pozza, S. D. Pletcher, C. M. Gendron, and V. D.
Longo, 2001Regulation of longevity and stress resistance by
Sch9 in yeast. Science 292: 288–290.
Fadri, M., A. Daquinag, S. Wang, T. Xue, and J. Kunz, 2005
pleckstrin homology domain proteins Slm1 and Slm2 are re-
quired for actin cytoskeleton organization in yeast and bind
phosphatidylinositol-4,5-bisphosphate and TORC2. Mol. Biol.
Cell 16: 1883–1900.
Elucidating TOR signaling
TOR complex 2: a signaling
The Npr1 kinase
Cell growth control: little
Nutrients, via the Tor
R. Loewith and M. N. Hall
Fingerman, I., V. Nagaraj, D. Norris, and A. K. Vershon, 2003
plays a key role in yeast ribosome biogenesis. Eukaryot. Cell 2:
Flinn, R. J., Y. Yan, S. Goswami, P. J. Parker, and J. M. Backer,
2010The late endosome is essential for mTORC1 signaling.
Mol. Biol. Cell 21: 833–841.
Freckleton, G., S. I. Lippman, J. R. Broach, and S. Tavazoie,
2009Microarray profiling of phage-display selections for rapid
mapping of transcription factor-DNA interactions. PLoS Genet.
Friant, S., R. Lombardi, T. Schmelzle, M. N. Hall, and H. Riezman,
2001Sphingoid base signaling via Pkh kinases is required for
endocytosis in yeast. EMBO J. 20: 6783–6792.
Gander, S., D. Bonenfant, P. Altermatt, D. E. Martin, S. Hauri
et al., 2008Identification of the rapamycin-sensitive phos-
phorylation sites within the Ser/Thr-rich domain of the yeast
Npr1 protein kinase. Rapid Commun. Mass Spectrom. 22:
Garcia-Martinez, J. M., and D. R. Alessi, 2008
(mTORC2) controls hydrophobic motif phosphorylation and ac-
tivation of serum- and glucocorticoid-induced protein kinase 1
(SGK1). Biochem. J. 416: 375–385.
Gasch, A. P., and M. Werner-Washburne, 2002
yeast responses to environmental stress and starvation. Funct.
Integr. Genomics 2: 181–192.
Georis, I., A. Feller, J. J. Tate, T. G. Cooper, and E. Dubois,
2009a Nitrogen catabolite repression-sensitive transcription
as a readout of Tor pathway regulation: the genetic background,
reporter gene and GATA factor assayed determine the outcomes.
Genetics 181: 861–874.
Georis, I., A. Feller, F. Vierendeels, and E. Dubois, 2009b
yeast GATA factor Gat1 occupies a central position in nitrogen
catabolite repression-sensitive gene activation. Mol. Cell. Biol.
Gong, R., L. Li, Y. Liu, P. Wang, H. Yang et al., 2011
structure of the Gtr1p-Gtr2p complex reveals new insights into
the amino acid-induced TORC1 activation. Genes Dev. 25:
Goranov, A. I., and A. Amon, 2010
a one-way road. Curr. Opin. Cell Biol. 22: 795–800.
Grigull, J., S. Mnaimneh, J. Pootoolal, M. D. Robinson, and T. R.
Hughes, 2004Genome-wide analysis of mRNA stability using
transcription inhibitors and microarrays reveals posttranscrip-
tional control of ribosome biogenesis factors. Mol. Cell. Biol.
Guba, M., P. von Breitenbuch, M. Steinbauer, G. Koehl, S. Flegel
et al., 2002 Rapamycin inhibits primary and metastatic tumor
growth by antiangiogenesis: involvement of vascular endothe-
lial growth factor. Nat. Med. 8: 128–135.
Hall, D. B., J. T. Wade, and K. Struhl, 2006
Hmo1, associates with promoters of many ribosomal protein
genes and throughout the rRNA gene locus in Saccharomyces
cerevisiae. Mol. Cell. Biol. 26: 3672–3679.
Hall, M. N., 1996 The TOR signalling pathway and growth con-
trol in yeast. Biochem. Soc. Trans. 24: 234–239.
Han, S., M. A. Lone, R. Schneiter, and A. Chang, 2010
Orm2 are conserved endoplasmic reticulum membrane proteins
regulating lipid homeostasis and protein quality control. Proc.
Natl. Acad. Sci. USA 107: 5851–5856.
Hara, K., K. Yonezawa, Q. P. Weng, M. T. Kozlowski, C. Belham
et al., 1998Amino acid sufficiency and mTOR regulate p70 S6
kinase and eIF-4E BP1 through a common effector mechanism.
J. Biol. Chem. 273: 14484–14494.
Hara, K., Y. Maruki, X. Long, K. Yoshino, N. Oshiro et al.,
2002Raptor, a binding partner of target of rapamycin
(TOR), mediates TOR action. Cell 110: 177–189.
mTOR complex 2
The genomics of
Growth and division: not
An HMG protein,
Hardt, M., N. Chantaravisoot, and F. Tamanoi, 2011
mutations of TOR (target of rapamycin). Genes Cells 16: 141–
Hardwick, J. S., F. G. Kuruvilla, J. K. Tong, A. F. Shamji, and S. L.
Schreiber, 1999Rapamycin-modulated transcription defines
the subset of nutrient-sensitive signaling pathways directly con-
trolled by the Tor proteins. Proc. Natl. Acad. Sci. USA 96:
Harrison, D. E., R. Strong, Z. D. Sharp, J. F. Nelson, C. M. Astle
et al., 2009Rapamycin fed late in life extends lifespan in ge-
netically heterogeneous mice. Nature 460: 392–395.
Heitman, J., N. R. Movva, and M. N. Hall, 1991a
cycle arrest by the immunosuppressant rapamycin in yeast. Sci-
ence 253: 905–909.
Heitman, J., N. R. Movva, P. C. Hiestand, and M. N. Hall,
1991bFK 506-binding protein proline rotamase is a target
for the immunosuppressive agent FK 506 in Saccharomyces cer-
evisiae. Proc. Natl. Acad. Sci. USA 88: 1948–1952.
Heitman, J., N. R. Movva, and M. N. Hall, 1992
merases at the crossroads of protein folding, signal transduc-
tion, and immunosuppression. New Biol. 4: 448–460.
Helliwell, S. B., P. Wagner, J. Kunz, M. Deuter-Reinhard, R. Henriquez
et al., 1994 TOR1 and TOR2 are structurally and functionally similar
Biol. Cell 5: 105–118.
Helliwell, S. B., I. Howald, N. Barbet, and M. N. Hall,
1998aTOR2 is part of two related signaling pathways coordi-
nating cell growth in Saccharomyces cerevisiae. Genetics 148:
Helliwell, S. B., A. Schmidt, Y. Ohya, and M. N. Hall, 1998b
Rho1 effector Pkc1, but not Bni1, mediates signalling from Tor2
to the actin cytoskeleton. Curr. Biol. 8: 1211–1214.
Hinnebusch, A. G., 2005Translational regulation of GCN4 and
the general amino acid control of yeast. Annu. Rev. Microbiol.
Honma, Y., A. Kitamura, R. Shioda, H. Maruyama, K. Ozaki et al.,
2006TOR regulates late steps of ribosome maturation in the
nucleoplasm via Nog1 in response to nutrients. EMBO J. 25:
Hou, H., K. Subramanian, T. J. LaGrassa, D. Markgraf, L. E. Dietrich
et al., 2005The DHHC protein Pfa3 affects vacuole-associated
palmitoylation of the fusion factor Vac8. Proc. Natl. Acad. Sci.
USA 102: 17366–17371.
Huber, A., B. Bodenmiller, A. Uotila, M. Stahl, S. Wanka et al.,
2009Characterization of the rapamycin-sensitive phosphopro-
teome reveals that Sch9 is a central coordinator of protein syn-
thesis. Genes Dev. 23: 1929–1943.
Huber, A., S. L. French, H. Tekotte, S. Yerlikaya, M. Stahl et al.,
2011Sch9 regulates ribosome biogenesis via Stb3, Dot6 and
Tod6 and the histone deacetylase complex RPD3L. EMBO J. 30:
Inoue, Y., and D. J. Klionsky, 2010
in Saccharomyces cerevisiae. Semin. Cell Dev. Biol. 21: 664–
Jacinto, E., and A. Lorberg, 2008
in yeast and mammals. Biochem. J. 410: 19–37.
Jacinto, E., B. Guo, K. T. Arndt, T. Schmelzle, and M. N. Hall,
2001TIP41 interacts with TAP42 and negatively regulates
the TOR signaling pathway. Mol. Cell 8: 1017–1026.
Jacinto, E., R. Loewith, A. Schmidt, S. Lin, M. A. Ruegg et al.,
2004Mammalian TOR complex 2 controls the actin cytoskel-
eton and is rapamycin insensitive. Nat. Cell Biol. 6: 1122–1128.
Jia, K., D. Chen, and D. L. Riddle, 2004
acts with the insulin signaling pathway to regulate C. elegans
larval development, metabolism and life span. Development
Targets for cell
Regulation of macroautophagy
TOR regulation of AGC kinases
The TOR pathway inter-
Jiang, Y., and J. R. Broach, 1999
phatase 2A reciprocally regulate Tap42 in controlling cell
growth in yeast. EMBO J. 18: 2782–2792.
Jones, K. T., E. R. Greer, D. Pearce, and K. Ashrafi, 2009
TORC2 regulates Caenorhabditis elegans fat storage, body size,
and development through sgk-1. PLoS Biol. 7: e60.
Jordens, J., V. Janssens, S. Longin, I. Stevens, E. Martens et al.,
2006The protein phosphatase 2A phosphatase activator is
a novel peptidyl-prolyl cis/trans-isomerase. J. Biol. Chem. 281:
Jorgensen, P., J. L. Nishikawa, B. J. Breitkreutz, and M. Tyers,
2002Systematic identification of pathways that couple cell
growth and division in yeast. Science 297: 395–400.
Jorgensen, P., I. Rupes, J. R. Sharom, L. Schneper, J. R. Broach
et al., 2004 A dynamic transcriptional network communicates
growth potential to ribosome synthesis and critical cell size.
Genes Dev. 18: 2491–2505.
Kaeberlein, M., and B. K. Kennedy, 2011
search: protein translation and TOR signaling, 2010. Aging Cell
Kaeberlein, M., R. W. Powers III. K. K. Steffen, E. A. Westman, D.
Hu et al., 2005 Regulation of yeast replicative life span by TOR
and Sch9 in response to nutrients. Science 310: 1193–1196.
Kaizu, K., S. Ghosh, Y. Matsuoka, H. Moriya, Y. Shimizu-Yoshida
et al., 2010A comprehensive molecular interaction map of the
budding yeast cell cycle. Mol. Syst. Biol. 6: 415.
Kamada, Y., Y. Fujioka, N. N. Suzuki, F. Inagaki, S. Wullschleger
et al., 2005Tor2 directly phosphorylates the AGC kinase Ypk2
to regulate actin polarization. Mol. Cell. Biol. 25: 7239–7248.
Kamada, Y., K. Yoshino, C. Kondo, T. Kawamata, N. Oshiro et al.,
2010Tor directly controls the Atg1 kinase complex to regulate
autophagy. Mol. Cell. Biol. 30: 1049–1058.
Kapahi, P., B. M. Zid, T. Harper, D. Koslover, V. Sapin et al.,
2004 Regulation of lifespan in Drosophila by modulation of
genes in the TOR signaling pathway. Curr. Biol. 14: 885–890.
Kapahi, P., D. Chen, A. N. Rogers, S. D. Katewa, P. W. Li et al.,
2010With TOR, less is more: a key role for the conserved
nutrient-sensing TOR pathway in aging. Cell Metab. 11: 453–
Keith, C. T., and S. L. Schreiber, 1995
repair, recombination, and cell cycle checkpoints. Science 270:
Kijanska, M., I. Dohnal, W. Reiter, S. Kaspar, I. Stoffel et al.,
2010Activation of Atg1 kinase in autophagy by regulated
phosphorylation. Autophagy 6: 1168–1178.
Kim, D. H., D. D. Sarbassov, S. M. Ali, J. E. King, R. R. Latek et al.,
2002 mTOR interacts with raptor to form a nutrient-sensitive
complex that signals to the cell growth machinery. Cell 110:
Kim, E., P. Goraksha-Hicks, L. Li, T. P. Neufeld, and K. L. Guan,
2008Regulation of TORC1 by Rag GTPases in nutrient re-
sponse. Nat. Cell Biol. 10: 935–945.
Kim, J., and Guan, K. L. (2011). Amino acid signaling in TOR
activation. Annu. Rev. Biochem. 80: 1001–1032.
Kogan, K., E. D. Spear, C. A. Kaiser, and D. Fass, 2010
conservation of components in the amino acid sensing branch of
the TOR pathway in yeast and mammals. J. Mol. Biol. 402: 388–
Koltin, Y., L. Faucette, D. J. Bergsma, M. A. Levy, R. Cafferkey et al.,
1991Rapamycin sensitivity in Saccharomyces cerevisiae is
mediated by a peptidyl-prolyl cis-trans isomerase related to hu-
man FK506-binding protein. Mol. Cell. Biol. 11: 1718–1723.
Komeili, A., K. P. Wedaman, E. K. O’Shea, and T. Powers,
2000 Mechanism of metabolic control. Target of rapamycin
signaling links nitrogen quality to the activity of the Rtg1 and
Rtg3 transcription factors. J. Cell Biol. 151: 863–878.
Tor proteins and protein phos-
Hot topics in aging re-
PIK-related kinases: DNA
Krause, S. A., and J. V. Gray, 2002
is required for viability in quiescence in Saccharomyces cerevi-
siae. Curr. Biol. 12: 588–593.
Kuepfer, L., M. Peter, U. Sauer, and J. Stelling, 2007
modeling for analysis of cell signaling dynamics. Nat. Biotech-
nol. 25: 1001–1006.
Kunz, J., and M. N. Hall, 1993
mycin: more than just immunosuppression. Trends Biochem.
Sci. 18: 334–338.
Kunz, J., R. Henriquez, U. Schneider, M. Deuter-Reinhard, N. R.
Movva et al., 1993Target of rapamycin in yeast, TOR2, is an
essential phosphatidylinositol kinase homolog required for G1
progression. Cell 73: 585–596.
Kunz, J., U. Schneider, I. Howald, A. Schmidt, and M. N. Hall,
2000HEAT repeats mediate plasma membrane localization
of Tor2p in yeast. J. Biol. Chem. 275: 37011–37020.
Kuranda, K., V. Leberre, S. Sokol, G. Palamarczyk, and J. Francois,
2006Investigating the caffeine effects in the yeast Saccharo-
myces cerevisiae brings new insights into the connection be-
tween TOR, PKC and Ras/cAMP signalling pathways. Mol.
Microbiol. 61: 1147–1166.
Laferte, A., E. Favry, A. Sentenac, M. Riva, C. Carles et al.,
2006The transcriptional activity of RNA polymerase I is
a key determinant for the level of all ribosome components.
Genes Dev. 20: 2030–2040.
Lee, J., R. D. Moir, and I. M. Willis, 2009
polymerase III transcription involves SCH9-dependent and
SCH9-independent branches of the target of rapamycin (TOR)
pathway. J. Biol. Chem. 284: 12604–12608.
Lee, T. I., N. J. Rinaldi, F. Robert, D. T. Odom, Z. Bar-Joseph et al.,
2002Transcriptional regulatory networks in Saccharomyces
cerevisiae. Science 298: 799–804.
Lempiainen, H., and D. Shore, 2009
biogenesis. Curr. Opin. Cell Biol. 21: 855–863.
Lempiainen, H., A. Uotila, J. Urban, I. Dohnal, G. Ammerer et al.,
2009Sfp1 interaction with TORC1 and Mrs6 reveals feedback
regulation on TOR signaling. Mol. Cell 33: 704–716.
Levin, D. E., 2005 Cell wall integrity signaling in Saccharomyces
cerevisiae. Microbiol. Mol. Biol. Rev. 69: 262–291.
Li, H., C. K. Tsang, M. Watkins, P. G. Bertram, and X. F. Zheng,
2006 Nutrient regulates Tor1 nuclear localization and associ-
ation with rDNA promoter. Nature 442: 1058–1061.
Liko, D., M. G. Slattery, and W. Heideman, 2007
ribosomal RNA processing element motifs that control transcrip-
tional responses to growth in Saccharomyces cerevisiae. J. Biol.
Chem. 282: 26623–26628.
Liko, D., M. K. Conway, D. S. Grunwald, and W. Heideman
2010Stb3 plays a role in the glucose-induced transition from
quiescence to growth in Saccharomyces cerevisiae. Genetics 185:
Lin, C. H., J. A. MacGurn, T. Chu, C. J. Stefan, and S. D. Emr,
2008Arrestin-related ubiquitin-ligase adaptors regulate endo-
cytosis and protein turnover at the cell surface. Cell 135: 714–
Lippman, S. I., and J. R. Broach, 2009
TORC1 activate genes for ribosomal biogenesis by inactivating
repressors encoded by Dot6 and its homolog Tod6. Proc. Natl.
Acad. Sci. USA 106: 19928–19933.
Liu, K., X. Zhang, R. L. Lester, and R. C. Dickson, 2005
goid long chain base phytosphingosine activates AGC-type pro-
tein kinases in Saccharomyces cerevisiae including Ypk1, Ypk2,
and Sch9. J. Biol. Chem. 280: 22679–22687.
Liu, Z., and R. A. Butow, 2006
ing. Annu. Rev. Genet. 40: 159–185.
Liu, Z., T. Sekito, M. Spirek, J. Thornton, and R. A. Butow,
2003Retrograde signaling is regulated by the dynamic inter-
action between Rtg2p and Mks1p. Mol. Cell 12: 401–411.
The protein kinase C pathway
Cyclosporin A, FK506 and rapa-
Regulation of RNA
Growth control and ribosome
Stb3 binds to
Protein kinase A and
Mitochondrial retrograde signal-
R. Loewith and M. N. Hall
Ljungdahl, P. O., 2009
SPS-sensing pathway in yeast. Biochem. Soc. Trans. 37: 242–
Loewith, R., 2010TORC1 signaling in budding yeast, pp. 147–
176 in The Enzymes, edited by M. N. Hall, and F. Tamanoi.
Academic Press/Elsevier, New York.
Loewith, R., 2011A brief history of TOR. Biochem. Soc. Trans.
Loewith, R., and M. N. Hall, 2004
poral and spatial control of cell growth, pp. 139–166 in Cell
Growth: Control of Cell Size, edited by M. N. Hall, M. Raff, and
G. Thomas. Cold Spring Harbor Laboratory Press, Cold Spring
Loewith, R., E. Jacinto, S. Wullschleger, A. Lorberg, J. L. Crespo
et al., 2002 Two TOR complexes, only one of which is rapa-
mycin sensitive, have distinct roles in cell growth control. Mol.
Cell 10: 457–468.
Lorenz, M. C., and J. Heitman, 1995
resistance by preventing interaction with FKBP12-rapamycin. J. Biol.
Chem. 270: 27531–27537.
Luo, X., N. Talarek, and C. De Virgilio, 2011
G 0 program requires Igo1 and Igo2, which antagonize activa-
tion of decapping of specific nutrient-regulated mRNAs. RNA
Biol. 8: 14–17.
Madeo, F., T. Eisenberg, S. Buttner, C. Ruckenstuhl, and G.
Kroemer, 2010a Spermidine: a novel autophagy inducer and
longevity elixir. Autophagy 6: 160–162.
Madeo, F., N. Tavernarakis, and G. Kroemer, 2010b
agy promote longevity? Nat. Cell Biol. 12: 842–846.
Magasanik, B., and C. A. Kaiser, 2002
Saccharomyces cerevisiae. Gene 290: 1–18.
Marion, R. M., A. Regev, E. Segal, Y. Barash, D. Koller et al.,
2004Sfp1 is a stress- and nutrient-sensitive regulator of ribo-
somal protein gene expression. Proc. Natl. Acad. Sci. USA 101:
Martin, D. E., A. Soulard, and M. N. Hall, 2004
ribosomal protein gene expression via PKA and the Forkhead
transcription factor FHL1. Cell 119: 969–979.
2003Schizosaccharomyces pombe AGC family kinase Gad8p
forms a conserved signaling module with TOR and PDK1-like
kinases. EMBO J. 22: 3073–3083.
Michels, A. A., 2011 MAF1: a new target of mTORC1. Biochem.
Soc. Trans. 39: 487–491.
Morselli, E., G. Marino, M. V. Bennetzen, T. Eisenberg, E. Megalou
et al., 2011Spermidine and resveratrol induce autophagy by
distinct pathways converging on the acetylproteome. J. Cell
Biol. 192: 615–629.
Mulet, J. M., D. E. Martin, R. Loewith, and M. N. Hall,
2006Mutual antagonism of target of rapamycin and calci-
neurin signaling. J. Biol. Chem. 281: 33000–33007.
Nakashima, A., Y. Maruki, Y. Imamura, C. Kondo, T. Kawamata
et al., 2008 The yeast Tor signaling pathway is involved in
G2/M transition via polo-kinase. PLoS ONE 3: e2223.
Nakatogawa, H.,K. Suzuki,
2009 Dynamics and diversity in autophagy mechanisms: les-
sons from yeast. Nat. Rev. Mol. Cell Biol. 10: 458–467.
Nikko, E., and H. R. Pelham, 2009
of yeast plasma membrane transporters. Traffic 10: 1856–1867.
Nikko, E., J. A. Sullivan, and H. R. Pelham, 2008
proteins mediate ubiquitination and endocytosis of the yeast
metal transporter Smf1. EMBO Rep. 9: 1216–1221.
O’Donnell, A. F., A. Apffel, R. G. Gardner, and M. S. Cyert,
2010Alpha-arrestins Aly1 and Aly2 regulate intracellular traf-
ficking in response to nutrient signaling. Mol. Biol. Cell 21:
Amino-acid-induced signalling via the
TOR signaling in yeast: tem-
TOR mutations confer rapamycin
Initiation of the yeast
Nitrogen regulation in
Y. Kamada, andY. Ohsumi,
Oficjalska-Pham, D., O. Harismendy, W. J. Smagowicz, A. Gonzalez
de Peredo, M. Boguta et al., 2006
polymerase III transcription is triggered by protein phosphatase
type 2A-mediated dephosphorylation of Maf1. Mol. Cell 22:
Ohne, Y., T. Takahara, R. Hatakeyama, T. Matsuzaki, M. Noda
et al., 2008Isolation of hyperactive mutants of mammalian
target of rapamycin. J. Biol. Chem. 283: 31861–31870.
Pan, Y., E. A. Schroeder, A. Ocampo, A. Barrientos, and G. S.
Shadel, 2011Regulation of yeast chronological life span by
TORC1 via adaptive mitochondrial ROS signaling. Cell Metab.
Pearce, L. R., D. Komander, and D. R. Alessi, 2010
bolts of AGC protein kinases. Nat. Rev. Mol. Cell Biol. 11: 9–22.
Perry, J., and N. Kleckner, 2003
giant HEAT repeat proteins. Cell 112: 151–155.
Polak, P., and M. N. Hall, 2009
body metabolism. Curr. Opin. Cell Biol. 21: 209–218.
Powers, R. W. III. M. Kaeberlein, S. D. Caldwell, B. K. Kennedy, and
S. Fields, 2006 Extension of chronological life span in yeast by
decreased TOR pathway signaling. Genes Dev. 20: 174–184.
Powers, T., 2007TOR signaling and S6 kinase 1: yeast catches
up. Cell Metab. 6: 1–2.
Powers, T., and P. Walter, 1999
genesis by the rapamycin-sensitive TOR-signaling pathway in
Saccharomyces cerevisiae. Mol. Biol. Cell 10: 987–1000.
Powers, T., S. Aranova, and B. Niles, 2010
biosynthesis and signaling: lessons from budding yeast,
pp. 177–197 in The Enzymes: Structure, Function and Regulation
of TOR Complexes from Yeast to Mammals, edited by M. N. Hall
and F. Tamanoi. Academic Press, San Diego.
Ramachandran, V., and P. K. Herman, 2011
tions between the cAMP-dependent protein kinase and Tor sig-
naling pathways modulate cell growth in Saccharomyces
cerevisiae. Genetics 187: 441–454.
Reina, J. H., T. N. Azzouz, and N. Hernandez, 2006
player in the regulation of human RNA polymerase III transcrip-
tion. PLoS ONE 1: e134.
Reinders, J., R. P. Zahedi, N. Pfanner, C. Meisinger, and
A. Sickmann, 2006 Toward the complete yeast mitochondrial
proteome: multidimensional separation techniques for mito-
chondrial proteomics. J. Proteome Res. 5: 1543–1554.
Reinke, A., S. Anderson, J. M. McCaffery, J. Yates III. S. Aronova
et al., 2004 TOR complex 1 includes a novel component,
Tco89p (YPL180w), and cooperates with Ssd1p to maintain
cellular integrity in Saccharomyces cerevisiae. J. Biol. Chem.
Reinke, A., J. C. Chen, S. Aronova, and T. Powers, 2006
targets TOR complex I and provides evidence for a regulatory
link between the FRB and kinase domains of Tor1p. J. Biol.
Chem. 281: 31616–31626.
Reiter, A., R. Steinbauer, A. Philippi, J. Gerber, H. Tschochner et al.,
2011 Reduction in ribosomal protein synthesis is sufficient to
explain major effects on ribosome production after short-term
TOR inactivation in Saccharomyces cerevisiae. Mol. Cell. Biol.
Roelants, F. M., P. D. Torrance, N. Bezman, and J. Thorner,
2002Pkh1 and Pkh2 differentially phosphorylate and activate
Ypk1 and Ykr2 and define protein kinase modules required for
maintenance of cell wall integrity. Mol. Biol. Cell 13: 3005–
Roelants, F. M., P. D. Torrance, and J. Thorner, 2004
roles of PDK1- and PDK2-phosphorylation sites in the yeast AGC
kinases Ypk1, Pkc1 and Sch9. Microbiology 150: 3289–3304.
Rohde, J., J. Heitman, and M. E. Cardenas, 2001
link nutrient sensing to cell growth. J. Biol. Chem. 276: 9583–
General repression of RNA
The nuts and
The ATRs, ATMs, and TORs are
mTOR and the control of whole
Regulation of ribosome bio-
TORC2 and spingolipid
Maf1, a new
The TOR kinases
Rudra, D., Y. Zhao, and J. R. Warner, 2005
Fhl1p interaction in the synthesis of yeast ribosomal proteins.
EMBO J. 24: 533–542.
Sabatini, D. M., H. Erdjument-Bromage, M. Lui, P. Tempst, and S.
H. Snyder, 1994RAFT1: a mammalian protein that binds to
FKBP12 in a rapamycin-dependent fashion and is homologous
to yeast TORs. Cell 78: 35–43.
Sabers, C. J., M. M. Martin, G. J. Brunn, J. M. Williams, F. J.
Dumont et al., 1995Isolation of a protein target of the
FKBP12-rapamycin complex in mammalian cells. J. Biol. Chem.
Sancak, Y., T. R. Peterson, Y. D. Shaul, R. A. Lindquist, C. C.
Thoreen et al., 2008 The Rag GTPases bind raptor and medi-
ate amino acid signaling to mTORC1. Science 320: 1496–1501.
Sancak, Y., L. Bar-Peled, R. Zoncu, A. L. Markhard, S. Nada et al.,
2010 Ragulator-Rag complex targets mTORC1 to the lyso-
somal surface and is necessary for its activation by amino acids.
Cell 141: 290–303.
Sarbassov, D. D., S. M. Ali, D. H. Kim, D. A. Guertin, R. R. Latek
et al., 2004 Rictor, a novel binding partner of mTOR, defines
a rapamycin-insensitive and raptor-independent pathway that
regulates the cytoskeleton. Curr. Biol. 14: 1296–1302.
Schawalder, S. B., M. Kabani, I. Howald, U. Choudhury, M. Werner
et al., 2004Growth-regulated recruitment of the essential
yeast ribosomal protein gene activator Ifh1. Nature 432:
Schmelzle, T., and M. N. Hall, 2000
cell growth. Cell 103: 253–262.
Schmelzle, T., S. B. Helliwell, and M. N. Hall, 2002
kinases and the RHO1 exchange factor TUS1 are novel compo-
nents of the cell integrity pathway in yeast. Mol. Cell. Biol. 22:
Schmelzle, T., T. Beck,D.
2004Activation of the RAS/cyclic AMP pathway suppresses
a TOR deficiency in yeast. Mol. Cell. Biol. 24: 338–351.
Schmidt, A., J. Kunz, and M. N. Hall, 1996
organization of the actin cytoskeleton in yeast. Proc. Natl. Acad.
Sci. USA 93: 13780–13785.
Schmidt, A., M. Bickle, T. Beck, and M. N. Hall, 1997
phosphatidylinositol kinase homolog TOR2 activates RHO1 and
RHO2 via the exchange factor ROM2. Cell 88: 531–542.
Schmidt, A., T. Beck, A. Koller, J. Kunz, and M. N. Hall, 1998
TOR nutrient signalling pathway phosphorylates NPR1 and in-
hibits turnover of the tryptophan permease. EMBO J. 17: 6924–
Schreiber, S. L., 1991 Chemistry and biology of the immunophilins
and their immunosuppressive ligands. Science 251: 283–287.
Shamji, A. F., F. G. Kuruvilla, and S. L. Schreiber, 2000
tioning the transcriptional program induced by rapamycin
among the effectors of the Tor proteins. Curr. Biol. 10: 1574–
Shen, C., C. S. Lancaster, B. Shi, H. Guo, P. Thimmaiah et al.,
2007TOR signaling is a determinant of cell survival in re-
sponse to DNA damage. Mol. Cell. Biol. 27: 7007–7017.
Shen, H., and M. R. Green, 2006
signals and promote splicing by a common mechanism in yeast
through humans. Genes Dev. 20: 1755–1765.
Shin, C. S., S. Y. Kim, and W. K. Huh, 2009
degradation of the transcription factor Stp1, a key effector of
the SPS amino-acid-sensing pathway in Saccharomyces cerevi-
siae. J. Cell Sci. 122: 2089–2099.
Singh, J., and M. Tyers, 2009 A Rab escort protein integrates the
secretion system with TOR signaling and ribosome biogenesis.
Genes Dev. 23: 1944–1958.
Soetens, O., J. O. De Craene, and B. Andre, 2001
required for sorting to the vacuole of the yeast general amino
acid permease, Gap1. J. Biol. Chem. 276: 43949–43957.
Central role of Ifh1p-
TOR, a central controller of
TOR2 is required for
RS domains contact splicing
Soukas, A. A., E. A. Kane, C. E. Carr, J. A. Melo, and G. Ruvkun,
growth, and life span in Caenorhabditis elegans. Genes Dev.
Soulard, A., A. Cohen, and M. N. Hall, 2009
invertebrates. Curr. Opin. Cell Biol. 21: 825–836.
Soulard, A., A. Cremonesi, S. Moes, F. Schutz, P. Jeno et al.,
2010 The rapamycin-sensitive phosphoproteome reveals that
TOR controls protein kinase A toward some but not all sub-
strates. Mol. Biol. Cell 21: 3475–3486.
Stan, R., M. M. McLaughlin, R. Cafferkey, R. K. Johnson, M. Rosenberg
et al., 1994Interaction between FKBP12-rapamycin and TOR in-
volves a conserved serine residue. J. Biol. Chem. 269: 32027–
Steffen, K. K., V. L. MacKay, E. O. Kerr, M. Tsuchiya, D. Hu et al.,
2008Yeast life span extension by depletion of 60s ribosomal
subunits is mediated by Gcn4. Cell 133: 292–302.
Sturgill, T. W., and M. N. Hall, 2009
are in similar structures as oncogenic mutations in PI3KCalpha.
ACS Chem. Biol. 4: 999–1015.
Sturgill, T. W., A. Cohen, M. Diefenbacher, M. Trautwein, D. E.
Martin et al., 2008TOR1 and TOR2 have distinct locations
in live cells. Eukaryot. Cell 7: 1819–1830.
Sun, Y., R. Taniguchi, D. Tanoue, T. Yamaji, H. Takematsu et al.,
2000 Sli2 (Ypk1), a homologue of mammalian protein kinase
SGK, is a downstream kinase in the sphingolipid-mediated sig-
naling pathway of yeast. Mol. Cell. Biol. 20: 4411–4419.
Tabuchi, M., A. Audhya, A. B. Parsons, C. Boone, and S. D. Emr,
2006The phosphatidylinositol 4,5-biphosphate and TORC2
binding proteins Slm1 and Slm2 function in sphingolipid regu-
lation. Mol. Cell. Biol. 26: 5861–5875.
Talarek, N., E. Cameroni, M. Jaquenoud, X. Luo, S. Bontron et al.,
2010 Initiation of the TORC1-regulated G0 program requires
Igo1/2, which license specific mRNAs to evade degradation via
the 59-39 mRNA decay pathway. Mol. Cell 38: 345–355.
Tanida, I., M. Yanagida, N. Maki, S. Yagi, F. Namiyama et al.,
1991 Yeast cyclophilin-related gene encodes a nonessential
second peptidyl-prolyl cis-trans isomerase associated with the
secretory pathway. Transplant. Proc. 23: 2856–2861.
Tate, J. J., I. Georis, A. Feller, E. Dubois, and T. G. Cooper,
2009 Rapamycin-induced Gln3 dephosphorylation is insuffi-
cient for nuclear localization: Sit4 and PP2A phosphatases are
regulated and function differently. J. Biol. Chem. 284: 2522–
Tate, J. J., I. Georis, E. Dubois, and T. G. Cooper, 2010
phosphatase requirements and GATA factor responses to nitro-
gen catabolite repression and rapamycin treatment in Saccha-
romyces cerevisiae. J. Biol. Chem. 285: 17880–17895.
Teixeira, M. C., T. R. Cabrito, Z. M. Hanif, R. C. Vargas, S. Tenreiro
et al., 2010Yeast response and tolerance to polyamine toxicity
involving the drug H+ antiporter Qdr3 and the transcription
factors Yap1 and Gcn4. Microbiology 157: 945–956.
Thomas, G., and M. N. Hall, 1997
cell growth. Curr. Opin. Cell Biol. 9: 782–787.
Torres, J., C. J. Di Como, E. Herrero, and M. A. De La Torre-Ruiz,
2002Regulation of the cell integrity pathway by rapamycin-
sensitive TOR function in budding yeast. J. Biol. Chem. 277:
Tschochner, H., and E. Hurt, 2003
from the nucleolus to the cytoplasm. Trends Cell Biol. 13:
Unal, E., B. Kinde, and A. Amon, 2011
age-induced cellular damage and resets life span in yeast. Sci-
ence 332: 1554–1557.
Upadhya, R., J. Lee, and I. M. Willis, 2002
mediator of diverse signals that repress RNA polymerase III
transcription. Mol. Cell 10: 1489–1494.
TOR signaling in
Activating mutations in TOR
TOR signalling and control of
Pre-ribosomes on the road
Maf1 is an essential
R. Loewith and M. N. Hall
Urano, J., T. Sato, T. Matsuo, Y. Otsubo, M. Yamamoto et al., Download full-text
2007 Point mutations in TOR confer Rheb-independent
growth in fission yeast and nutrient-independent mammalian
TOR signaling in mammalian cells. Proc. Natl. Acad. Sci. USA
Urban, J., A. Soulard, A. Huber, S. Lippman, D. Mukhopadhyay
et al., 2007Sch9 is a major target of TORC1 in Saccharomyces
cerevisiae. Mol. Cell 26: 663–674.
Van Belle, D., and B. Andre, 2001
brane transporters. Curr. Opin. Cell Biol. 13: 389–398.
Vannini, A., R. Ringel, A. G. Kusser, O. Berninghausen, G. A.
Kassavetis et al., 2010Molecular basis of RNA polymerase
III transcription repression by Maf1. Cell 143: 59–70.
Vellai, T., K. Takacs-Vellai, Y. Zhang, A. L. Kovacs, L. Orosz et al.,
2003 Genetics: influence of TOR kinase on lifespan in C.
elegans. Nature 426: 620.
Wade, J. T., D. B. Hall, and K. Struhl, 2004
factor Ifh1 is a key regulator of yeast ribosomal protein genes.
Nature 432: 1054–1058.
Wanke, V., I. Pedruzzi, E. Cameroni, F. Dubouloz, and C. De Virgilio,
2005Regulation of G0 entry by the Pho80-Pho85 cyclin-CDK
complex. EMBO J. 24: 4271–4278.
Wanke, V., E. Cameroni, A. Uotila, M. Piccolis, J. Urban et al.,
2008 Caffeine extends yeast lifespan by targeting TORC1.
Mol. Microbiol. 69: 277–285.
Warner, J. R., 1999 The economics of ribosome biosynthesis in
yeast. Trends Biochem. Sci. 24: 437–440.
Wedaman, K. P., A. Reinke, S. Anderson, J. Yates III. J. M. McCaffery
et al., 2003 Tor kinases are in distinct membrane-associated
protein complexes in Saccharomyces cerevisiae. Mol. Biol. Cell
Wei, M., P. Fabrizio, J. Hu, H. Ge, C. Cheng et al., 2008
extension by calorie restriction depends on Rim15 and tran-
scription factors downstream of Ras/PKA, Tor, and Sch9. PLoS
Genet. 4: e13.
Wei, Y., and X. S. Zheng, 2010 Maf1 regulation: a model of signal
transduction inside the nucleus. Nucleus 1: 162–165.
Wei, Y., C. K. Tsang, and X. F. Zheng, 2009
ulation of RNA polymerase III-dependent transcription by
TORC1. EMBO J. 28: 2220–2230.
Weindruch, R., and R. L. Walford, 1988
and Disease by Dietary Restriction. Charles C Thomas, Spring-
Wiederrecht, G., L. Brizuela, K. Elliston, N. H. Sigal, and J. J.
Siekierka, 1991FKB1 encodes a nonessential FK 506-binding
protein in Saccharomyces cerevisiae and contains regions sug-
gesting homology to the cyclophilins. Proc. Natl. Acad. Sci.
USA 88: 1029–1033.
Wullschleger, S., R. Loewith, W. Oppliger, and M. N. Hall,
2005Molecular organization of target of rapamycin complex
2. J. Biol. Chem. 280: 30697–30704.
A genomic view of yeast mem-
Mechanisms of reg-
The Retardation of Aging
Wullschleger, S., R. Loewith, and M. N. Hall, 2006
in growth and metabolism. Cell 124: 471–484.
Yan, G., X. Shen, and Y. Jiang, 2006
associated phosphatases by abrogating their association with
Tor complex 1. EMBO J. 25: 3546–3555.
Yang, Z., and D. J. Klionsky, 2010
autophagy. Nat. Cell Biol. 12: 814–822.
Yeh, Y. Y.,K. Wrasman, and P. K.Herman, 2010
within the Atg1 activation loop is required for both kinase activity
and the induction of autophagy in Saccharomyces cerevisiae. Genetics
Yip, C. K., K. Murata, T. Walz, D. M. Sabatini, and S. A. Kang,
2010 Structure of the human mTOR complex I and its impli-
cations for rapamycin inhibition. Mol. Cell 38: 768–774.
Yorimitsu, T., C. He, K. Wang, and D. J. Klionsky, 2009
associated protein phosphatase type 2A negatively regulates in-
duction of autophagy. Autophagy 5: 616–624.
Zaragoza, D., A. Ghavidel, J. Heitman, and M. C. Schultz,
1998Rapamycin induces the G0 program of transcriptional
repression in yeast by interfering with the TOR signaling path-
way. Mol. Cell. Biol. 18: 4463–4470.
Zheng, X. F., D. Florentino, J. Chen, G. R. Crabtree, and S. L.
Schreiber, 1995TOR kinase domains are required for two dis-
tinct functions, only one of which is inhibited by rapamycin. Cell
Zheng, Y., and Y. Jiang, 2005The yeast phosphotyrosyl phospha-
tase activator is part of the Tap42-phosphatase complexes. Mol.
Biol. Cell 16: 2119–2127.
Zhu, C., K. J. Byers, R. P. McCord, Z. Shi, M. F. Berger et al.,
2009 High-resolution DNA-binding specificity analysis of yeast
transcription factors. Genome Res. 19: 556–566.
Zinzalla, V., T. W. Sturgill, and M. N. Hall, 2010
composition, structure and phosphorylation, pp. 1–20 in The
Enzymes: Structure, Function and Regulation of TOR Complexes
from Yeast to Mammals, edited by M. N. Hall and F. Tamanoi.
Academic Press, San Diego.
2011Activation of mTORC2 by association with the ribosome.
Cell 144: 757–768.
Zoncu, R., A. Efeyan, and D. M. Sabatini, 2011
growth signal integration to cancer, diabetes and ageing. Nat.
Rev. Mol. Cell Biol. 12: 21–35.
Zurita-Martinez, S. A., and M. E. Cardenas, 2005
AMP-protein kinase A: two parallel pathways regulating expres-
sion of genes required for cell growth. Eukaryot. Cell 4: 63–71.
Zurita-Martinez, S. A., R. Puria, X. Pan, J. D. Boeke, and M. E.
Cardenas, 2007Efficient Tor signaling requires a functional
class C Vps protein complex in Saccharomyces cerevisiae. Genet-
ics 176: 2139–2150.
Rapamycin activates Tap42-
Eaten alive: a history of macro-
Oppliger, and M.N. Hall,
Tor and cyclic
Communicating editor: J. Thorner