Article

Yeast Ataxin-7 links histone deubiquitination with gene gating and mRNA export

Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany.
Nature Cell Biology (Impact Factor: 19.68). 07/2008; 10(6):707-15. DOI: 10.1038/ncb1733
Source: PubMed

ABSTRACT

Targeting of a gene to the nuclear pore complexes (NPCs), known as gene gating, can affect its transcriptional state. However, the mechanism underlying gene gating is poorly understood. Here, we have identified SAGA-associated Sgf73 (ref. 10), the yeast orthologue of human Ataxin-7 (ref. 11), as a regulator of histone H2B ubiquitin levels, a modification linked to both transcription initiation and elongation. Sgf73 is a key component of a minimal histone-deubiquitinating complex. Activation of the H2B deubiquitinating protease, Ubp8, is cooperative and requires complex formation with the amino-terminal zinc-finger-containing domain of Sgf73 and Sgf11-Sus1. Through a separate domain, Sgf73 mediates recruitment of the TREX-2 mRNA export factors Sac3 and Thp1 to SAGA and their stable interaction with Sus1-Cdc31. This latter step is crucial to target TREX-2 to the NPC. Loss of Sgf73 from SAGA abrogates gene gating of GAL1 and causes a GAL1 mRNA export defect. Thus, Sgf73 provides a molecular scaffold to integrate the regulation of H2B ubiquitin levels, tethering of a gene to the NPC and export of mRNA.

Download full-text

Full-text

Available from: Ed Hurt, Jul 09, 2015
  • Source
    • "A relay between nucleoporins and transcription could operate through an intermediate layer of adaptor proteins. Known candidates are the chromatin modifier SAGA (Kö hler et al., 2008; Rodríguez-Navarro et al., 2004), the THO complex (Rougemaille et al., 2008), and the TREX-2 complex (Cabal et al., 2006). Specialized promoter elements (Ahmed et al., 2010) and the post-translational modification of transcription factors (Texari et al., 2013) further contribute to transient gene-NPC contacts. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Nuclear pore complexes (NPCs) influence gene expression besides their established function in nuclear transport. The TREX-2 complex localizes to the NPC basket and affects gene-NPC interactions, transcription, and mRNA export. How TREX-2 regulates the gene expression machinery is unknown. Here, we show that TREX-2 interacts with the Mediator complex, an essential regulator of RNA Polymerase (Pol) II. Structural and biochemical studies identify a conserved region on TREX-2, which directly binds the Mediator Med31/Med7N submodule. TREX-2 regulates assembly of Mediator with the Cdk8 kinase and is required for recruitment and site-specific phosphorylation of Pol II. Transcriptome and phenotypic profiling confirm that TREX-2 and Med31 are functionally interdependent at specific genes. TREX-2 additionally uses its Mediator-interacting surface to regulate mRNA export suggesting a mechanism for coupling transcription initiation and early steps of mRNA processing. Our data provide mechanistic insight into how an NPC-associated adaptor complex accesses the core transcription machinery. Copyright © 2015 Elsevier Inc. All rights reserved.
    Full-text · Article · Aug 2015 · Cell
  • Source
    • "Previous work has indicated that Mex67:Mtr2 binds primarily to the N-terminal region of Sac3 (Fischer et al., 2002). In yeast, TREX-2 also facilitates the localization of many actively transcribing genes, such as GAL1, to NPCs, which in turn facilitates the removal of repression mediated by de-ubiquitinylation by Ulp1 (Texari et al., 2013) and, through interactions between TREX-2 and the SAGA complex, can couple transcription, processing, and polyadenylation with the export of mature mRNAs to the cytoplasm (Rodriguez-Navarro et al., 2004; Kö hler et al., 2008). Although crystal structures have been obtained for parts of the Saccharomyces TREX-2 complex, such as Sac3 CID bound to Sus1 and Cdc31 (Jani et al., 2009, 2014 "
    [Show abstract] [Hide abstract]
    ABSTRACT: The TREX-2 complex integrates mRNA nuclear export into the gene expression pathway and is based on a Sac3 scaffold to which Thp1, Sem1, Sus1, and Cdc31 bind. TREX-2 also binds the mRNA nuclear export factor, Mex67:Mtr2, through the Sac3 N-terminal region (Sac3N). Here, we characterize Chaetomium thermophilum TREX-2, show that the in vitro reconstituted complex has an annular structure, and define the structural basis for interactions between Sac3, Sus1, Cdc31, and Mex67:Mtr2. Crystal structures show that the binding of C. thermophilum Sac3N to the Mex67 NTF2-like domain (Mex67(NTF2L)) is mediated primarily through phenylalanine residues present in a series of repeating sequence motifs that resemble those seen in many nucleoporins, and Mlp1 also binds Mex67:Mtr2 using a similar motif. Deletion of Sac3N generated growth and mRNA export defects in Saccharomyces cerevisiae, and we propose TREX-2 and Mlp1 function to facilitate export by concentrating mature messenger ribonucleoparticles at the nuclear pore entrance. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.
    Full-text · Article · Jun 2015 · Structure
  • Source
    • "Sus1 has other functions in addition to its activity in SAGA, which may make its role in yeast RLS unpredictable. Strains lacking both SGF73 and UBP8 have lifespans identical to the SGF73 single deletion, consistent with the prediction that both deletions enhance lifespan by a similar mechanism and cause increased levels of ubiquitinated H2B (Figure S1B) (Kö hler et al., 2008). "
    [Show abstract] [Hide abstract]
    ABSTRACT: We have analyzed the yeast replicative lifespan of a large number of open reading frame (ORF) deletions. Here, we report that strains lacking genes SGF73, SGF11, and UBP8 encoding SAGA/SLIK complex histone deubiquitinase module (DUBm) components are exceptionally long lived. Strains lacking other SAGA/SALSA components, including the acetyltransferase encoded by GCN5, are not long lived; however, these genes are required for the lifespan extension observed in DUBm deletions. Moreover, the SIR2-encoded histone deacetylase is required, and we document both a genetic and physical interaction between DUBm and Sir2. A series of studies assessing Sir2-dependent functions lead us to propose that DUBm strains are exceptionally long lived because they promote multiple prolongevity events, including reduced rDNA recombination and altered silencing of telomere-proximal genes. Given that ataxin-7, the human Sgf73 ortholog, causes the neurodegenerative disease spinocerebellar ataxia type 7, our findings indicate that the genetic and epigenetic interactions between DUBm and SIR2 will be relevant to neurodegeneration and aging.
    Full-text · Article · Jul 2014 · Cell Reports
Show more