[Show abstract][Hide abstract] ABSTRACT: In many organisms, polo kinases appear to play multiple roles during M-phase progression. To provide new insights into the function of the budding yeast polo kinase Cdc5, we generated novel temperature-sensitive cdc5 mutants by mutagenizing the C-terminal noncatalytic polo box domain, a region that is critical for proper subcellular localization. One of these mutants, cdc5-11, exhibited a temperature-sensitive growth defect with an abnormal spindle morphology. Strikingly, provision of a moderate level of benomyl, a microtubule-depolymerizing drug, permitted cdc5-11 cells to grow significantly better than the isogenic CDC5 wild type in a FEAR (cdc Fourteen Early Anaphase Release)-independent manner. In addition, cdc5-11 required MAD2 for both cell growth and the benomyl-remedial phenotype. These results suggest that cdc5-11 is defective in proper spindle function. Consistent with this view, cdc5-11 exhibited abnormal spindle morphology, shorter spindle length, and delayed microtubule regrowth at the nonpermissive temperature. Overexpression of CDC5 moderately rescued the spc98-2 growth defect. Interestingly, both Cdc28 and Cdc5 were required for the proper modification of the spindle pole body components Nud1, Slk19, and Stu2 in vivo. They also phosphorylated these three proteins in vitro. Taken together, these observations suggest that concerted action of Cdc28 and Cdc5 on Nud1, Slk19, and Stu2 is important for proper spindle functions.
[Show abstract][Hide abstract] ABSTRACT: In budding yeast, Gin4, a Nim1-related kinase, plays an important role in proper organization of the septin ring at the mother-bud
neck, a filamentous structure that is critical for diverse cellular processes including mitotic entry and cytokinesis. How
Gin4 kinase activity is regulated is not known. Here we showed that a neck-associated Ser/Thr kinase Elm1, which is important
for septin assembly, is critical for proper modification of Gin4 and its physiological substrate Shs1. In vitro studies with purified recombinant proteins demonstrated that Elm1 directly phosphorylates and activates Gin4, which in turn
phosphorylates Shs1. Consistent with these observations, acute inhibition of Elm1 activity abolished mitotic Gin4 phosphorylation
and Gin4-dependent Shs1 modification in vivo. In addition, a gin4 mutant lacking the Elm1-dependent phosphorylation sites exhibited an impaired localization to the bud-neck
and, as a result, induced a significant growth defect with an elongated bud morphology. Thus, Elm1 regulates the septin assembly-dependent
cellular events by directly phosphorylating and activating the Gin4-dependent pathway(s).
[Show abstract][Hide abstract] ABSTRACT: The polo-like kinases (Plks) are a conserved subfamily of Ser/Thr protein kinases that play pivotal roles in regulating various cellular and biochemical events at multiple stages of M phase. Genetic and biochemical data revealed that both the budding yeast and the fission yeast polo kinase homologs (Cdc5 and Plo1, respectively) bear remarkable functional similarities with those in metazoan organisms, suggesting that the role of Plks is largely conserved throughout evolution. Thus, studies on Plks in genetically amenable lower eucaryotic organisms may yield valuable insights into the function of Plks in higher eucaryotic organisms. In this review, common properties and distinct functions of Cdc5 and Plo1 will be discussed and compared to properties and functions of Plks in higher eucaryotic organisms.
[Show abstract][Hide abstract] ABSTRACT: Budding yeast polo kinase Cdc5p localizes to the spindle pole body (SPB) and to the bud-neck and plays multiple roles during M-phase progression. To dissect localization-specific mitotic functions of Cdc5p, we tethered a localization-defective N-terminal kinase domain of Cdc5p (Cdc5pDeltaC) to the SPB or to the bud-neck with components specifically localizing to one of these sites and characterized these mutants in a cdc5Delta background. Characterization of a viable, SPB-localizing, CDC5DeltaC-CNM67 mutant revealed that it is defective in timely degradation of Swe1p, a negative regulator of Cdc28p. Loss of BFA1, a negative regulator of mitotic exit, rescued the lethality of a neck-localizing CDC5DeltaC-CDC12 or CDC5DeltaC-CDC3 mutant but yielded severe defects in cytokinesis. These data suggest that the SPB-associated Cdc5p activity is critical for both mitotic exit and cytokinesis, whereas the bud neck-localized Cdc5p is required for proper Swe1p regulation. Interestingly, a cdc5Delta bfa1Delta swe1Delta triple mutant is viable but grows slowly, whereas cdc5Delta cells bearing both CDC5DeltaC-CNM67 and CDC5DeltaC-CDC12 grow well with only a mild cell cycle delay. Thus, SPB- and the bud-neck-localized Cdc5p control most of the critical Cdc5p functions and downregulation of Bfa1p and Swe1p at the respective locations are two critical factors that require Cdc5p.
[Show abstract][Hide abstract] ABSTRACT: The polo-box domain of the budding yeast polo kinase Cdc5p plays an essential role for targeting the catalytic activity of Cdc5p to spindle pole bodies (SPBs) and cytokinetic neck-filaments. Here, we report the isolation of Bbp1p as a polo-box interacting protein by a yeast two-hybrid screen. Bbp1p localizes to the periphery of the central plaque of the SPB and plays an important role in SPB duplication. Similarly, Cdc5p localized to the cytoplasmic periphery of the SPB. In vitro binding studies showed that Cdc5p interacted with the N-terminal domain of Bbp1p (Bbp1pDeltaC), but apparently not with Mps2p, a component shown to form a stable complex with Bbp1p. In addition, Bbp1p, but likely not Mps2p, was required for proper localization of Cdc5p to the SPB. The C-terminal coiled-coil domain of Bbp1p (Bbp1p(243-385)), which is crucial for both the homodimerization and the SPB localization, could target the localization-defective Cdc5pDeltaC to the SPB and induce the release of Cdc14p from the nucleolus. Consistent with this observation, expression of CDC5DeltaC-BBP1(243-385) under CDC5 promoter control partially complemented the cdc5Delta defect. These data suggest that Bbp1pDeltaC interacts with the polo-box domain of Cdc5p, and this interaction is critical for the subcellular localization and mitotic functions of Cdc5p.
Molecular Biology of the Cell 05/2004; 15(4):1711-23. DOI:10.1091/mbc.E03-07-0461 · 4.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In eukaryotes, cyclin B-bound cyclin-dependent protein kinase 1 promotes mitotic entry but is held in check, in part, by Wee1 protein kinase. Timely mitotic entry in budding yeast requires inactivation of Swe1 (Wee1 ortholog). Perturbations of the septin collar at the bud neck lead to Swe1 stabilization, delaying the G(2)/M transition. Swe1 is recruited to the neck and hyperphosphorylated before ubiquitin-mediated degradation. Hsl1 kinase (Nim1 ortholog), a negative regulator of Wee1, is required for efficient Swe1 localization at the neck but seems not to phosphorylate Swe1. Here, we show that two other kinases targeted sequentially to the neck, Cla4/PAK and Cdc5/Polo, are responsible for stepwise phosphorylation and down-regulation of Swe1. This mechanism links assembly of a cellular structure to passage into mitosis.
Proceedings of the National Academy of Sciences 04/2004; 101(12):4124-9. DOI:10.1073/pnas.0400641101 · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the budding yeast Saccharomyces cerevisiae, the Cdc3p, Cdc10p, Cdc11p, Cdc12p, and Sep7p/Shs1p septins assemble early in the cell cycle in a ring that marks the future
cytokinetic site. The septins appear to be major structural components of a set of filaments at the mother-bud neck and function
as a scaffold for recruiting proteins involved in cytokinesis and other processes. We isolated a novel gene, BNI5, as a dosage suppressor of the cdc12-6 growth defect. Overexpression of BNI5 also suppressed the growth defects of cdc10-1, cdc11-6, and sep7Δ strains. Loss of BNI5 resulted in a cytokinesis defect, as evidenced by the formation of connected cells with shared cytoplasms, and deletion of
BNI5 in a cdc3-6, cdc10-1, cdc11-6, cdc12-6, or sep7Δ mutant strain resulted in enhanced defects in septin localization and cytokinesis. Bni5p localizes to the mother-bud neck
in a septin-dependent manner shortly after bud emergence and disappears from the neck approximately 2 to 3 min before spindle
disassembly. Two-hybrid, in vitro binding, and protein-localization studies suggest that Bni5p interacts with the N-terminal
domain of Cdc11p, which also appears to be sufficient for the localization of Cdc11p, its interaction with other septins,
and other critical aspects of its function. Our data suggest that the Bni5p-septin interaction is important for septin ring
stability and function, which is in turn critical for normal cytokinesis.