Relationships between rDNA, Nop1 and Sir complex in biotechnologically relevant distillery yeasts

Yeast Sir2 deacetylase is a component of the silent information regulator (SIR) complex encompassing Sir2/Sir3/Sir4. Sir2 is recruited to telomeres through Rap1, and this complex spreads into subtelomeric DNA via histone deacetylation. However, potential functions at telomeres for SIRT1, the mammalian orthologue of yeast Sir2, are less clear. We studied both loss of function (SIRT1 deficient) and gain of function (SIRT1super) mouse models. Our results indicate that SIRT1 is a positive regulator of telomere length in vivo and attenuates telomere shortening associated with aging, an effect dependent on telomerase activity. Using chromatin immunoprecipitation assays, we find that SIRT1 interacts with telomeric repeats in vivo. In addition, SIRT1 overexpression increases homologous recombination throughout the entire genome, including telomeres, centromeres, and chromosome arms. These findings link SIRT1 to telomere biology and global DNA repair and provide new mechanistic explanations for the known functions of SIRT1 in protection from DNA damage and some age-associated pathologies.

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Multiple Interactions in Sir Protein Recruitment by Rap1p at Silencers and Telomeres in Yeast

Molecular and Cellular Biology ◽

10.1128/mcb.21.23.8082-8094.2001 ◽

2001 ◽

Vol 21 (23) ◽

pp. 8082-8094 ◽

Cited By ~ 64

Author(s):

Paolo Moretti ◽

David Shore

Keyword(s):

Complex Formation ◽

Mating Type ◽

Small Region ◽

Carboxyl Terminus ◽

Silent Chromatin ◽

Histone Binding ◽

Amino Terminal ◽

Sir Complex ◽

Two Hybrid

ABSTRACT Initiation of transcriptional silencing at mating type loci and telomeres in Saccharomyces cerevisiaerequires the recruitment of a Sir2/3/4 (silent information regulator) protein complex to the chromosome, which occurs at least in part through its association with the silencer- and telomere-binding protein Rap1p. Sir3p and Sir4p are structural components of silent chromatin that can self-associate, interact with each other, and bind to the amino-terminal tails of histones H3 and H4. We have identified a small region of Sir3p between amino acids 455 and 481 that is necessary and sufficient for association with the carboxyl terminus of Rap1p but not required for Sir complex formation or histone binding.SIR3 mutations that delete this region cause a silencing defect at HMR and telomeres. However, this impairment of repression is considerably less than that displayed by Rap1p carboxy-terminal truncations that are defective in Sir3p binding. This difference may be explained by the ability of the Rap1p carboxyl terminus to interact independently with Sir4p, which we demonstrate by in vitro binding and two-hybrid assays. Significantly, the Rap1p-Sir4p two-hybrid interaction does not require Sir3p and is abolished by mutation of the carboxyl terminus of Rap1p. We propose that both Sir3p and Sir4p can directly and independently bind to Rap1p at mating type silencers and telomeres and suggest that Rap1p-mediated recruitment of Sir proteins operates through multiple cooperative interactions, at least some of which are redundant. The physical separation of the Rap1p interaction region of Sir3p from parts of the protein required for Sir complex formation and histone binding raises the possibility that Rap1p can participate directly in the maintenance of silent chromatin through the stabilization of Sir complex-nucleosome interactions.

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Quiescent Saccharomyces cerevisiae forms telomere hyperclusters at the nuclear membrane vicinity through a multifaceted mechanism involving Esc1, the Sir complex, and chromatin condensation

Molecular Biology of the Cell ◽

10.1091/mbc.e16-01-0069 ◽

2016 ◽

Vol 27 (12) ◽

pp. 1875-1884 ◽

Cited By ~ 23

Author(s):

Damien Laporte ◽

Fabien Courtout ◽

Sylvain Tollis ◽

Isabelle Sagot

Keyword(s):

Saccharomyces Cerevisiae ◽

Nuclear Membrane ◽

Chromatin Condensation ◽

Histone H1 ◽

Chromosome Condensation ◽

Histone H4 ◽

Microtubule Bundle ◽

Quiescent Cells ◽

Nuclear Reorganization ◽

Sir Complex

Like other eukaryotes, Saccharomyces cerevisiae spatially organizes its chromosomes within the nucleus. In G1 phase, the yeast’s 32 telomeres are clustered into 6–10 foci that dynamically interact with the nuclear membrane. Here we show that, when cells leave the division cycle and enter quiescence, telomeres gather into two to three hyperclusters at the nuclear membrane vicinity. This localization depends on Esc1 but not on the Ku proteins. Telomere hypercluster formation requires the Sir complex but is independent of the nuclear microtubule bundle that specifically assembles in quiescent cells. Importantly, mutants deleted for the linker histone H1 Hho1 or defective in condensin activity or affected for histone H4 Lys-16 deacetylation are impaired, at least in part, for telomere hypercluster formation in quiescence, suggesting that this process involves chromosome condensation. Finally, we establish that telomere hypercluster formation is not necessary for quiescence establishment, maintenance, and exit, raising the question of the physiological raison d’être of this nuclear reorganization.

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Faculty Opinions recommendation of Assembly of the SIR complex and its regulation by O-acetyl-ADP-ribose, a product of NAD-dependent histone deacetylation.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1026070.323924 ◽

2005 ◽

Author(s):

Dieter A Wolf

Keyword(s):

Histone Deacetylation ◽

Sir Complex

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SIR complex

The Dictionary of Genomics, Transcriptomics and Proteomics ◽

10.1002/9783527678679.dg12051 ◽

2015 ◽

pp. 1-1

Keyword(s):

Sir Complex

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Silentinformationregulator complex (SIR complex)

The Dictionary of Genomics, Transcriptomics and Proteomics ◽

10.1002/9783527678679.dg11909 ◽

2015 ◽

pp. 1-1

Keyword(s):

Sir Complex

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Sir3-Nucleosome Interactions in Spreading of Silent Chromatin in Saccharomyces cerevisiae

Molecular and Cellular Biology ◽

10.1128/mcb.01210-08 ◽

2008 ◽

Vol 28 (22) ◽

pp. 6903-6918 ◽

Cited By ~ 34

Author(s):

Johannes R. Buchberger ◽

Megumi Onishi ◽

Geng Li ◽

Jan Seebacher ◽

Adam D. Rudner ◽

...

Keyword(s):

Saccharomyces Cerevisiae ◽

Binding Activity ◽

Chromatin Fiber ◽

Silent Chromatin ◽

Histone H4 ◽

Histone Binding ◽

Aaa Atpase ◽

Binding Domains ◽

Sir Complex

ABSTRACT Silent chromatin in Saccharomyces cerevisiae is established in a stepwise process involving the SIR complex, comprised of the histone deacetylase Sir2 and the structural components Sir3 and Sir4. The Sir3 protein, which is the primary histone-binding component of the SIR complex, forms oligomers in vitro and has been proposed to mediate the spreading of the SIR complex along the chromatin fiber. In order to analyze the role of Sir3 in the spreading of the SIR complex, we performed a targeted genetic screen for alleles of SIR3 that dominantly disrupt silencing. Most mutations mapped to a single surface in the conserved N-terminal BAH domain, while one, L738P, localized to the AAA ATPase-like domain within the C-terminal half of Sir3. The BAH point mutants, but not the L738P mutant, disrupted the interaction between Sir3 and nucleosomes. In contrast, Sir3-L738P bound the N-terminal tail of histone H4 more strongly than wild-type Sir3, indicating that misregulation of the Sir3 C-terminal histone-binding activity also disrupted spreading. Our results underscore the importance of proper interactions between Sir3 and the nucleosome in silent chromatin assembly. We propose a model for the spreading of the SIR complex along the chromatin fiber through the two distinct histone-binding domains in Sir3.

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