scholarly journals Dominant Mutants of the Saccharomyces cerevisiae ASF1 Histone Chaperone Bypass the Need for CAF-1 in Transcriptional Silencing by Altering Histone and Sir Protein Recruitment

Genetics ◽  
2006 ◽  
Vol 173 (2) ◽  
pp. 599-610 ◽  
Author(s):  
Beth A. Tamburini ◽  
Joshua J. Carson ◽  
Jeffrey G. Linger ◽  
Jessica K. Tyler
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Transcriptional Silencing ◽  
Histone Chaperone ◽  
Protein Recruitment ◽  
Dominant Mutants

scholarly journals Spt10 and Spt21 Are Required for Transcriptional Silencing in Saccharomyces cerevisiae

2010 ◽  
Vol 10 (1) ◽  
pp. 118-129 ◽  
Author(s):  
Jennifer S. Chang ◽  
Fred Winston
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Histone Modifications ◽  
Chromatin Structure ◽  
Transcriptional Silencing ◽  
Content Type ◽  
Histone Gene Expression ◽  
Dam Methylase ◽  
Genomic Regions ◽  
Histone Locus ◽  
Protein Recruitment

ABSTRACT In Saccharomyces cerevisiae , transcriptional silencing occurs at three classes of genomic regions: near the telomeres, at the silent mating type loci, and within the ribosomal DNA (rDNA) repeats. In all three cases, silencing depends upon several factors, including specific types of histone modifications. In this work we have investigated the roles in silencing for Spt10 and Spt21, two proteins previously shown to control transcription of particular histone genes. Building on a recent study showing that Spt10 is required for telomeric silencing, our results show that in both spt10 and spt21 mutants, silencing is reduced near telomeres and at HML α, while it is increased at the rDNA. Both spt10 and spt21 mutations cause modest effects on Sir protein recruitment and histone modifications at telomeric regions, and they cause significant changes in chromatin structure, as judged by its accessibility to dam methylase. These silencing and chromatin changes are not seen upon deletion of HTA2-HTB2 , the primary histone locus regulated by Spt10 and Spt21. These results suggest that Spt10 and Spt21 control silencing in S. cerevisiae by altering chromatin structure through roles beyond the control of histone gene expression.

scholarly journals Distribution of a Limited Sir2 Protein Pool Regulates the Strength of Yeast rDNA Silencing and Is Modulated by Sir4p

Genetics ◽  
1998 ◽  
Vol 149 (3) ◽  
pp. 1205-1219 ◽  
Author(s):  
Jeffrey S Smith ◽  
Carrie Baker Brachmann ◽  
Lorraine Pillus ◽  
Jef D Boeke
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Simple Model ◽  
Regulatory Mechanism ◽  
Transcriptional Silencing ◽  
Rdna Locus ◽  
Genetic Manipulations ◽  
Protein Levels ◽  
Endogenous Level ◽  
Protein Pool ◽  
Negative Effect

Abstract Transcriptional silencing in Saccharomyces cerevisiae occurs at the silent mating-type loci HML and HMR, at telomeres, and at the ribosomal DNA (rDNA) locus RDN1. Silencing in the rDNA occurs by a novel mechanism that depends on a single Silent Information Regulator (SIR) gene, SIR2. SIR4, essential for other silenced loci, paradoxically inhibits rDNA silencing. In this study, we elucidate a regulatory mechanism for rDNA silencing based on the finding that rDNA silencing strength directly correlates with cellular Sir2 protein levels. The endogenous level of Sir2p was shown to be limiting for rDNA silencing. Furthermore, small changes in Sir2p levels altered rDNA silencing strength. In rDNA silencing phenotypes, sir2 mutations were shown to be epistatic to sir4 mutations, indicating that SIR4 inhibition of rDNA silencing is mediated through SIR2. Furthermore, rDNA silencing is insensitive to SIR3 overexpression, but is severely reduced by overexpression of full-length Sir4p or a fragment of Sir4p that interacts with Sir2p. This negative effect of SIR4 overexpression was overridden by co-overexpression of SIR2, suggesting that SIR4 directly inhibits the rDNA silencing function of SIR2. Finally, genetic manipulations of SIR4 previously shown to promote extended life span also resulted in enhanced rDNA silencing. We propose a simple model in which telomeres act as regulators of rDNA silencing by competing for limiting amounts of Sir2 protein.

scholarly journals Mutational Analysis of the Sir3 BAH Domain Reveals Multiple Points of Interaction with Nucleosomes

2009 ◽  
Vol 29 (10) ◽  
pp. 2532-2545 ◽  
Author(s):  
Vinaya Sampath ◽  
Peihua Yuan ◽  
Isabel X. Wang ◽  
Evelyn Prugar ◽  
Fred van Leeuwen ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Mutational Analysis ◽  
Histone H3 ◽  
Transcriptional Silencing ◽  
In Vitro Experiments ◽  
Multiple Points ◽  
Alanine Residue ◽  
Bah Domain ◽  
Multiple Domains

ABSTRACT Sir3, a component of the transcriptional silencing complex in the yeast Saccharomyces cerevisiae, has an N-terminal BAH domain that is crucial for the protein's silencing function. Previous work has shown that the N-terminal alanine residue of Sir3 (Ala2) and its acetylation play an important role in silencing. Here we show that the silencing defects of Sir3 Ala2 mutants can be suppressed by mutations in histones H3 and H4, specifically, by H3 D77N and H4 H75Y mutations. Additionally, a mutational analysis demonstrates that three separate regions of the Sir3 BAH domain are important for its role in silencing. Many of these BAH mutations also can be suppressed by the H3 D77N and H4 H75Y mutations. In agreement with the results of others, in vitro experiments show that the Sir3 BAH domain can interact with partially purified nucleosomes. The silencing-defective BAH mutants are defective for this interaction. These results, together with the previously characterized interaction between the C-terminal region of Sir3 and the histone H3/H4 tails, suggest that Sir3 utilizes multiple domains to interact with nucleosomes.

scholarly journals Structure of the human histone chaperone FACT Spt16 N-terminal domain

2016 ◽  
Vol 72 (2) ◽  
pp. 121-128 ◽  
Author(s):  
G. Marcianò ◽  
D. T. Huang
Keyword(s):  
Crystal Structure ◽  
Saccharomyces Cerevisiae ◽  
Complex Surface ◽  
Histone Chaperone ◽  
Titration Calorimetry ◽  
Nucleosome Assembly ◽  
Surface Residue ◽  
Histone Binding ◽  
Terminal Domain ◽  
Heterodimeric Complex

The histone chaperone FACT plays an important role in facilitating nucleosome assembly and disassembly during transcription. FACT is a heterodimeric complex consisting of Spt16 and SSRP1. The N-terminal domain of Spt16 resembles an inactive aminopeptidase. How this domain contributes to the histone chaperone activity of FACT remains elusive. Here, the crystal structure of the N-terminal domain (NTD) of human Spt16 is reported at a resolution of 1.84 Å. The structure adopts an aminopeptidase-like fold similar to those of theSaccharomyces cerevisiaeandSchizosaccharomyces pombeSpt16 NTDs. Isothermal titration calorimetry analyses show that human Spt16 NTD binds histones H3/H4 with low-micromolar affinity, suggesting that Spt16 NTD may contribute to histone binding in the FACT complex. Surface-residue conservation and electrostatic analysis reveal a conserved acidic patch that may be involved in histone binding.

scholarly journals Structure/Function Analysis of the Hif1 Histone Chaperone in Saccharomyces cerevisiae

2021 ◽  
Author(s):  
Nora Saud Dannah
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Chromosome Segregation ◽  
Genome Stability ◽  
Function Analysis ◽  
Molecular Genetic ◽  
Histone Chaperone ◽  
Chromatin Assembly ◽  
Biological Processes ◽  
Genetic Approach ◽  
Yeast Saccharomyces Cerevisiae

Understanding the regulation of chromatin structure is a vital aspect of molecular biology regarding its influences on biological processes such as DNA replication, transcription (gene expression), DNA repair, chromosome segregation and recombination. In the budding yeast Saccharomyces cerevisiae, a histone chaperone called Hif1 has been found in the nuclei as having a functional role in chromatin assembly. Hif1 is a homolog of the human protein NASP that is involved in the maintenance of genome stability. Previously, Hif1 has been shown to physically interact with Hat1, Hat2 and H3/H4 to form the NuB4 complex directly involved in chromatin assembly. A molecular genetic approach was conducted to determine which domain of Hif1 is involved in the interaction with the HAT1 complex.

scholarly journals Nicotinamide Clearance by Pnc1 Directly Regulates Sir2-Mediated Silencing and Longevity

2004 ◽  
Vol 24 (3) ◽  
pp. 1301-1312 ◽  
Author(s):  
Christopher M. Gallo ◽  
Daniel L. Smith ◽  
Jeffrey S. Smith
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Nicotinic Acid ◽  
Life Span ◽  
Histone Deacetylase ◽  
Transcriptional Repression ◽  
Transcriptional Silencing ◽  
Inhibitory Effect ◽  
Salvage Pathway

ABSTRACT The Saccharomyces cerevisiae Sir2 protein is an NAD+-dependent histone deacetylase (HDAC) that functions in transcriptional silencing and longevity. The NAD+ salvage pathway protein, Npt1, regulates Sir2-mediated processes by maintaining a sufficiently high intracellular NAD+ concentration. However, another NAD+ salvage pathway component, Pnc1, modulates silencing independently of the NAD+ concentration. Nicotinamide (NAM) is a by-product of the Sir2 deacetylase reaction and is a natural Sir2 inhibitor. Pnc1 is a nicotinamidase that converts NAM to nicotinic acid. Here we show that recombinant Pnc1 stimulates Sir2 HDAC activity in vitro by preventing the accumulation of NAM produced by Sir2. In vivo, telomeric, rDNA, and HM silencing are differentially sensitive to inhibition by NAM. Furthermore, PNC1 overexpression suppresses the inhibitory effect of exogenously added NAM on silencing, life span, and Hst1-mediated transcriptional repression. Finally, we show that stress suppresses the inhibitory effect of NAM through the induction of PNC1 expression. Pnc1, therefore, positively regulates Sir2-mediated silencing and longevity by preventing the accumulation of intracellular NAM during times of stress.

scholarly journals SUM1-1, a dominant suppressor of SIR mutations in Saccharomyces cerevisiae, increases transcriptional silencing at telomeres and HM mating-type loci and decreases chromosome stability.

1996 ◽  
Vol 16 (8) ◽  
pp. 4281-4294 ◽  
Author(s):  
M H Chi ◽  
D Shore
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Mating Type ◽  
Transcriptional Silencing ◽  
Chromosome Loss ◽  
Yeast Saccharomyces Cerevisiae ◽  
Sir Proteins ◽  
Telomere Binding Protein ◽  
Single Allele ◽  
Dominant Suppressor

Transcriptional silencing in the yeast Saccharomyces cerevisiae occurs at HML and HMR mating-type loci and telomeres and requires the products of the silent information regulator (SIR) genes. Recent evidence suggests that the silencer- and telomere-binding protein Rap1p initiates silencing by recruiting a complex of Sir proteins to the chromosome, where they act in some way to modify chromatin structure or accessibility. A single allele of the SUM1gene (SUM1-1) which restores silencing at HM loci in strains mutant for any of the four SIR genes was identified a number of years ago. However, conflicting genetic results and the lack of other alleles of SUM1 made it difficult to surmise the wild-type function of SUM1 or the manner in which the SUM1-1 mutation restores silencing in sir mutant strains. Here we report the cloning and characterization of the SUM1 gene and the SUM1-1 mutant allele. Our results indicate that SUM1-1 is an unusual altered-function mutation that can bypass the need for SIR function in HM silencing and increase repression at telomeres. A sum1 deletion mutation has only minor effects on silencing in SIR strains and does not restore silencing in sir mutants. In addition to its effect on transcriptional silencing, the SUM1-1 mutation (but not a sum1 deletion) increases the rate of chromosome loss and cell death. We suggest several speculative models for the action of SUM1-1 in silencing based on these and other data.

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