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Dodson AE, Rine J. Donor Preference Meets Heterochromatin: Moonlighting Activities of a Recombinational Enhancer in Saccharomyces cerevisiae. Genetics 2016; 204:1065-1074. [PMID: 27655944 PMCID: PMC5105842 DOI: 10.1534/genetics.116.194696] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2016] [Accepted: 09/16/2016] [Indexed: 11/18/2022] Open
Abstract
In Saccharomyces cerevisiae, a small, intergenic region known as the recombination enhancer regulates donor selection during mating-type switching and also helps shape the conformation of chromosome III. Using an assay that detects transient losses of heterochromatic repression, we found that the recombination enhancer also acts at a distance in cis to modify the stability of gene silencing. In a mating-type-specific manner, the recombination enhancer destabilized the heterochromatic repression of a gene located ∼17 kbp away. This effect depended on a subregion of the recombination enhancer that is largely sufficient to determine donor preference. Therefore, this subregion affects both recombination and transcription from a distance. These observations identify a rare example of long-range transcriptional regulation in yeast and raise the question of whether other cis elements also mediate dual effects on recombination and gene expression.
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Affiliation(s)
- Anne E Dodson
- Department of Molecular and Cell Biology, California Institute for Quantitative Biosciences, University of California, Berkeley, California 94720-3220
| | - Jasper Rine
- Department of Molecular and Cell Biology, California Institute for Quantitative Biosciences, University of California, Berkeley, California 94720-3220
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2
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Young TJ, Kirchmaier AL. Cell cycle regulation of silent chromatin formation. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2014; 1819:303-312. [PMID: 24459732 DOI: 10.1016/j.bbagrm.2011.10.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
Abstract
Identical genes in two different cells can stably exist in alternate transcriptional states despite the dynamic changes that will occur to chromatin at that locus throughout the cell cycle. In mammals, this is achieved through epigenetic processes that regulate key developmental transitions and ensure stable patterns of gene expression during growth and differentiation. The budding yeast Saccharomyces cerevisiae utilizes silencing to control the expression state of genes encoding key regulatory factors for determining cell-type, ribosomal RNA levels and proper telomere function. Here, we review the composition of silent chromatin in S. cerevisiae, how silent chromatin is influenced by chromatin assembly and histone modifications and highlight several observations that have contributed to our understanding of the interplay between silent chromatin formation and stability and the cell cycle. This article is part of a Special Issue entitled: Histone chaperones and Chromatin assembly.
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Cell-cycle perturbations suppress the slow-growth defect of spt10Δ mutants in Saccharomyces cerevisiae. G3-GENES GENOMES GENETICS 2013; 3:573-83. [PMID: 23450643 PMCID: PMC3583463 DOI: 10.1534/g3.112.005389] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Accepted: 01/17/2013] [Indexed: 01/05/2023]
Abstract
Spt10 is a putative acetyltransferase of Saccharomyces cerevisiae that directly activates the transcription of histone genes. Deletion of SPT10 causes a severe slow growth phenotype, showing that Spt10 is critical for normal cell division. To gain insight into the function of Spt10, we identified mutations that impair or improve the growth of spt10 null (spt10Δ) mutants. Mutations that cause lethality in combination with spt10Δ include particular components of the SAGA complex as well as asf1Δ and hir1Δ. Partial suppressors of the spt10Δ growth defect include mutations that perturb cell-cycle progression through the G1/S transition, S phase, and G2/M. Consistent with these results, slowing of cell-cycle progression by treatment with hydroxyurea or growth on medium containing glycerol as the carbon source also partially suppresses the spt10Δ slow-growth defect. In addition, mutations that impair the Lsm1-7-Pat1 complex, which regulates decapping of polyadenylated mRNAs, also partially suppress the spt10Δ growth defect. Interestingly, suppression of the spt10Δ growth defect is not accompanied by a restoration of normal histone mRNA levels. These findings suggest that Spt10 has multiple roles during cell division.
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Kang YH, Lee CH, Seo YS. Dna2 on the road to Okazaki fragment processing and genome stability in eukaryotes. Crit Rev Biochem Mol Biol 2010; 45:71-96. [PMID: 20131965 DOI: 10.3109/10409230903578593] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
DNA replication is a primary mechanism for maintaining genome integrity, but it serves this purpose best by cooperating with other proteins involved in DNA repair and recombination. Unlike leading strand synthesis, lagging strand synthesis has a greater risk of faulty replication for several reasons: First, a significant part of DNA is synthesized by polymerase alpha, which lacks a proofreading function. Second, a great number of Okazaki fragments are synthesized, processed and ligated per cell division. Third, the principal mechanism of Okazaki fragment processing is via generation of flaps, which have the potential to form a variety of structures in their sequence context. Finally, many proteins for the lagging strand interact with factors involved in repair and recombination. Thus, lagging strand DNA synthesis could be the best example of a converging place of both replication and repair proteins. To achieve the risky task with extraordinary fidelity, Okazaki fragment processing may depend on multiple layers of redundant, but connected pathways. An essential Dna2 endonuclease/helicase plays a pivotal role in processing common structural intermediates that occur during diverse DNA metabolisms (e.g. lagging strand synthesis and telomere maintenance). Many roles of Dna2 suggest that the preemptive removal of long or structured flaps ultimately contributes to genome maintenance in eukaryotes. In this review, we describe the function of Dna2 in Okazaki fragment processing, and discuss its role in the maintenance of genome integrity with an emphasis on its functional interactions with other factors required for genome maintenance.
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Affiliation(s)
- Young-Hoon Kang
- Center for DNA Replication and Genome Instability, Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, Korea
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5
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Yu Q, Kuzmiak H, Olsen L, Kulkarni A, Fink E, Zou Y, Bi X. Saccharomyces cerevisiae Esc2p interacts with Sir2p through a small ubiquitin-like modifier (SUMO)-binding motif and regulates transcriptionally silent chromatin in a locus-dependent manner. J Biol Chem 2010; 285:7525-36. [PMID: 20048165 DOI: 10.1074/jbc.m109.016360] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Saccharomyces cerevisiae Esc2p is a member of a conserved family of proteins that contain small ubiquitin-like modifier (SUMO)-like domains. It has been implicated in transcriptional silencing and shown to interact with the silencing protein Sir2p in a two-hybrid analysis. However, little is known about how Esc2p regulates the structure of silent chromatin. We demonstrate here that ESC2 differentially regulates silent chromatin at telomeric, rDNA, and HM loci. Specifically, ESC2 is required for efficient telomeric silencing and Sir2p association with telomeric silent chromatin and for silencing and maintenance of silent chromatin structure at rDNA. On the other hand, ESC2 negatively regulates silencing at HML and HMR and destabilizes HML silent chromatin without affecting Sir2p association with chromatin. We present evidence that Esc2p is associated with both transcriptionally silent and active loci in the genome, and the abundance of Esc2p is not correlated with the chromatin state at a particular locus. Using affinity pull-down analyses, we show that Esc2p and Sir2p interact in vivo, and recombinant Esc2p and Sir2p interact directly. Moreover, we dissect Esc2p and identify a putative SUMO-binding motif that is necessary and sufficient for interacting with Sir2p and SUMO and is required for the function of Esc2p in transcriptional silencing.
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Affiliation(s)
- Qun Yu
- Department of Biology, University of Rochester, Rochester, New York 14627, USA
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6
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H3 k36 methylation helps determine the timing of cdc45 association with replication origins. PLoS One 2009; 4:e5882. [PMID: 19521516 PMCID: PMC2690658 DOI: 10.1371/journal.pone.0005882] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2008] [Accepted: 04/27/2009] [Indexed: 01/13/2023] Open
Abstract
BACKGROUND Replication origins fire at different times during S-phase. Such timing is determined by the chromosomal context, which includes the activity of nearby genes, telomeric position effects and chromatin structure, such as the acetylation state of the surrounding chromatin. Activation of replication origins involves the conversion of a pre-replicative complex to a replicative complex. A pivotal step during this conversion is the binding of the replication factor Cdc45, which associates with replication origins at approximately their time of activation in a manner partially controlled by histone acetylation. METHODOLOGY/PRINCIPAL FINDINGS Here we identify histone H3 K36 methylation (H3 K36me) by Set2 as a novel regulator of the time of Cdc45 association with replication origins. Deletion of SET2 abolishes all forms of H3 K36 methylation. This causes a delay in Cdc45 binding to origins and renders the dynamics of this interaction insensitive to the state of histone acetylation of the surrounding chromosomal region. Furthermore, a decrease in H3 K36me3 and a concomitant increase in H3 K36me1 around the time of Cdc45 binding to replication origins suggests opposing functions for these two methylation states. Indeed, we find K36me3 depleted from early firing origins when compared to late origins genomewide, supporting a delaying effect of this histone modification for the association of replication factors with origins. CONCLUSIONS/SIGNIFICANCE We propose a model in which K36me1 together with histone acetylation advance, while K36me3 and histone deacetylation delay, the time of Cdc45 association with replication origins. The involvement of the transcriptionally induced H3 K36 methylation mark in regulating the timing of Cdc45 binding to replication origins provides a novel means of how gene expression may affect origin dynamics during S-phase.
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Abstract
Sir1 establishes transcriptional silencing at the cryptic mating-type loci HMR and HML (HM loci) by recruiting the three other Sir proteins, Sir2, -3, and -4, that function directly in silenced chromatin. However, SIR1-independent mechanisms also contribute to recruiting the Sir2-4 proteins to the HM loci. A screen to elucidate SIR1-independent mechanisms that establish HMR silencing identified a mutation in YKU80. The role for Ku in silencing both HMR and HML was masked by SIR1. Ku's role in silencing the HM loci was distinct from its shared role with the nuclear architecture protein Esc1 in tethering the HM loci and telomeres to the nuclear periphery. The ability of high-copy SIR4 to rescue HMR silencing defects in sir1Delta cells required Ku, and chromatin immunoprecipitation (ChIP) experiments provided evidence that Ku contributed to Sir4's physical association with the HM loci in vivo. Additional ChIP experiments provided evidence that Ku functioned directly at the HM loci. Thus Ku and Sir1 had overlapping roles in silencing the HM loci.
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8
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Synthetic lethal screens identify gene silencing processes in yeast and implicate the acetylated amino terminus of Sir3 in recognition of the nucleosome core. Mol Cell Biol 2008; 28:3861-72. [PMID: 18391024 DOI: 10.1128/mcb.02050-07] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Dot1 methylates histone H3 lysine 79 (H3K79) on the nucleosome core and is involved in Sir protein-mediated silencing. Previous studies suggested that H3K79 methylation within euchromatin prevents nonspecific binding of the Sir proteins, which in turn facilitates binding of the Sir proteins in unmethylated silent chromatin. However, the mechanism by which the Sir protein binding is influenced by this modification is unclear. We performed genome-wide synthetic genetic array (SGA) analysis and identified interactions of DOT1 with SIR1 and POL32. The synthetic growth defects found by SGA analysis were attributed to the loss of mating type identity caused by a synthetic silencing defect. By using epistasis analysis, DOT1, SIR1, and POL32 could be placed in different pathways of silencing. Dot1 shared its silencing phenotypes with the NatA N-terminal acetyltransferase complex and the conserved N-terminal bromo adjacent homology (BAH) domain of Sir3 (a substrate of NatA). We classified all of these as affecting a common silencing process, and we show that mutations in this process lead to nonspecific binding of Sir3 to chromatin. Our results suggest that the BAH domain of Sir3 binds to histone H3K79 and that acetylation of the BAH domain is required for the binding specificity of Sir3 for nucleosomes unmethylated at H3K79.
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9
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Casey L, Patterson EE, Müller U, Fox CA. Conversion of a replication origin to a silencer through a pathway shared by a Forkhead transcription factor and an S phase cyclin. Mol Biol Cell 2007; 19:608-22. [PMID: 18045995 DOI: 10.1091/mbc.e07-04-0323] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Silencing of the mating-type locus HMR in Saccharomyces cerevisiae requires DNA elements called silencers. To establish HMR silencing, the origin recognition complex binds the HMR-E silencer and recruits the silent information regulator (Sir)1 protein. Sir1 in turn helps establish silencing by stabilizing binding of the other Sir proteins, Sir2-4. However, silencing is semistable even in sir1Delta cells, indicating that SIR1-independent establishment mechanisms exist. Furthermore, the requirement for SIR1 in silencing a sensitized version of HMR can be bypassed by high-copy expression of FKH1 (FKH1(hc)), a conserved forkhead transcription factor, or by deletion of the S phase cyclin CLB5 (clb5Delta). FKH1(hc) caused only a modest increase in Fkh1 levels but effectively reestablished Sir2-4 chromatin at HMR as determined by Sir3-directed chromatin immunoprecipitation. In addition, FKH1(hc) prolonged the cell cycle in a manner distinct from deletion of its close paralogue FKH2, and it created a cell cycle phenotype more reminiscent to that caused by a clb5Delta. Unexpectedly, and in contrast to SIR1, both FKH1(hc) and clb5Delta established silencing at HMR using the replication origins, ARS1 or ARSH4, as complete substitutes for HMR-E (HMRDeltaE::ARS). HMRDeltaE::ARS1 was a robust origin in CLB5 cells. However, initiation by HMRDeltaE::ARS1 was reduced by clb5Delta or FKH1(hc), whereas ARS1 at its native locus was unaffected. The CLB5-sensitivity of HMRDeltaE::ARS1 did not result from formation of Sir2-4 chromatin because sir2Delta did not rescue origin firing in clb5Delta cells. These and other data supported a model in which FKH1 and CLB5 modulated Sir2-4 chromatin and late-origin firing through opposing regulation of a common pathway.
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Affiliation(s)
- Laurieann Casey
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, USA
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10
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Agricola E, Verdone L, Di Mauro E, Caserta M. H4 acetylation does not replace H3 acetylation in chromatin remodelling and transcription activation of Adr1-dependent genes. Mol Microbiol 2007; 62:1433-46. [PMID: 17121596 DOI: 10.1111/j.1365-2958.2006.05451.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Histone acetylation regulates gene expression. Whether this is caused by a general increase in nucleosome fluidity due to charge neutralization or by a more specific code is still matter of debate. By using a set of glucose-repressed Adr1-dependent genes of Saccharomyces cerevisiae, whose transcription was previously shown to require both Gcn5 and Esa1, we asked how changes of histone acetylation patterns at the promoter nucleosomes regulate chromatin remodelling and activation. When the signal of glucose reduction reaches the cells, H4 acetylation is kept constant while an increase of H3 acetylation occurs, in an Adr1- and Gcn5-dependent manner. In cells lacking Gcn5 activity, the H3 acetylation increase does not occur and an unexpected increase of histone H4 acetylation is observed. Nevertheless, chromatin remodelling and transcription activation are impaired, suggesting that acetylation of H3 and H4 histones plays different roles.
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Affiliation(s)
- Eleonora Agricola
- Istituto Pasteur-Fondazione Cenci Bolognetti, c/o Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, 00185 Rome, Italy
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11
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Michel AH, Kornmann B, Dubrana K, Shore D. Spontaneous rDNA copy number variation modulates Sir2 levels and epigenetic gene silencing. Genes Dev 2005; 19:1199-210. [PMID: 15905408 PMCID: PMC1132006 DOI: 10.1101/gad.340205] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We show that in budding yeast large rDNA deletions arise frequently and cause an increase in telomeric and mating-type gene silencing proportional to repeat loss. Paradoxically, this increase in silencing is correlated with a highly specific down-regulation of SIR2, which encodes a deacetylase enzyme required for silencing. These apparently conflicting observations suggest that a large nucleolar pool of Sir2 is released upon rDNA loss and made available for telomeric and HM silencing, as well as down-regulation of SIR2 itself. Indeed, we present evidence for a reduction in the fraction of Sir2 colocalizing with the nucleolar marker Nop1, and for SIR2 autoregulation. Despite a decrease in the fraction of nucleolar Sir2, and in overall Sir2 protein levels, short rDNA strains display normal rDNA silencing and a lifespan indistinguishable from wild type. These observations reveal an unexpectedly large clonal variation in rDNA cluster size and point to the existence of a novel regulatory circuit, sensitive to rDNA copy number, that balances nucleolar and nonnucleolar pools of Sir2 protein.
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Affiliation(s)
- Agnès H Michel
- Department of Molecular Biology and NCCR Program "Frontiers in Genetics", University of Geneva, Sciences III, 30, quai Ernest-Ansermet, CH-1211, Geneva 4, Switzerland
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12
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Ray A, Hector RE, Roy N, Song JH, Berkner KL, Runge KW. Sir3p phosphorylation by the Slt2p pathway effects redistribution of silencing function and shortened lifespan. Nat Genet 2003; 33:522-6. [PMID: 12640455 DOI: 10.1038/ng1132] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2003] [Accepted: 02/21/2003] [Indexed: 11/09/2022]
Abstract
An organism's lifespan is modulated by environmental conditions. When nutrients are abundant, the metabolism of many organisms shifts to growth or reproduction at the expense of longer lifespan, whereas a scarcity of nutrients reverses this shift. These correlations suggest that organisms respond to environmental changes by altering their metabolism to promote either reproduction and growth or long life. The only previously reported signaling mechanism involved in this response is the nutrient-responsive insulin/insulin-like growth factor-1 receptor pathway. Here we report another pathway that controls the length of yeast lifespan. Commitment to cell growth activates the Slt2p MAP kinase pathway, which phosphorylates the transcriptional silencing protein Sir3p, resulting in a shorter lifespan. Elimination of the Sir3p phosphorylation site at Ser275 extended lifespan by 38%. Lifespan extension occurs by a mechanism that is independent of suppressing rDNA recombination. Thus, Slt2p is an enzymatic regulator of silencing function that couples commitment to cell growth and shorter lifespan.
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Affiliation(s)
- Alo Ray
- Department of Molecular Biology, NC20, Cleveland Clinic Foundation, Lerner Research Institute, 9500 Euclid Avenue, Cleveland, Ohio 44195, USA
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13
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Smith CM, Haimberger ZW, Johnson CO, Wolf AJ, Gafken PR, Zhang Z, Parthun MR, Gottschling DE. Heritable chromatin structure: mapping "memory" in histones H3 and H4. Proc Natl Acad Sci U S A 2002; 99 Suppl 4:16454-61. [PMID: 12196632 PMCID: PMC139908 DOI: 10.1073/pnas.182424999] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Telomeric position effect in Saccharomyces cerevisiae is a chromatin-mediated phenomenon in which telomere proximal genes are repressed (silenced) in a heritable, but reversible, fashion. Once a transcriptional state (active or silenced) is established, however, there is a strong tendency for that state to be propagated. Twenty-five years ago, H. Weintraub and colleagues suggested that such heritability could be mediated by posttranslational modification of chromatin [Weintraub, H., Flint, S. J., Leffak, I. M., Groudine, M. & Grainger, R. M. (1977) Cold Spring Harbor Symp. Quant. Biol. 42, 401-407]. To identify potential sites within the chromatin that might act as sources of "memory" for the heritable transmission, we performed a genetic screen to isolate mutant alleles of the histones H3 and H4 genes that would "lock" telomeric marker genes into a silenced state. We identified mutations in the NH(2)-terminal tail and core of both histones; most of the amino acid changes mapped adjacent to lysines that are known sites of acetylation or methylation. We developed a method using MS to quantify the level of acetylation at each lysine within the histone H4 NH(2)-terminal tail in these mutants. We discovered that each of these mutants had a dramatic reduction in the level of acetylation at lysine 12 within the histone H4 tail. We propose that this lysine serves as a "memory mark" for propagating the expression state of a telomeric gene: when it is unacetylated, silent chromatin will be inherited; when it is acetylated an active state will be inherited.
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Affiliation(s)
- Christine M Smith
- Division of Basic Sciences and Proteomics Facility, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109, USA
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Vogelauer M, Rubbi L, Lucas I, Brewer BJ, Grunstein M. Histone acetylation regulates the time of replication origin firing. Mol Cell 2002; 10:1223-33. [PMID: 12453428 DOI: 10.1016/s1097-2765(02)00702-5] [Citation(s) in RCA: 332] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The temporal firing of replication origins throughout S phase in yeast depends on unknown determinants within the adjacent chromosomal environment. We demonstrate here that the state of histone acetylation of surrounding chromatin is an important regulator of temporal firing. Deletion of RPD3 histone deacetylase causes earlier origin firing and concurrent binding of the replication factor Cdc45p to origins. In addition, increased acetylation of histones in the vicinity of the late origin ARS1412 by recruitment of the histone acetyltransferase Gcn5p causes ARS1412 alone to fire earlier. These data indicate that histone acetylation is a direct determinant of the timing of origin firing.
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Affiliation(s)
- Maria Vogelauer
- Department of Biological Chemistry, UCLA School of Medicine, Boyer Hall, University of California-Los Angeles, Los Angeles, CA 90095, USA
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15
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Affiliation(s)
- Fred van Leeuwen
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA
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16
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Kasulke D, Seitz S, Ehrenhofer-Murray AE. A role for the Saccharomyces cerevisiae RENT complex protein Net1 in HMR silencing. Genetics 2002; 161:1411-23. [PMID: 12196389 PMCID: PMC1462229 DOI: 10.1093/genetics/161.4.1411] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Silencing in the yeast Saccharomyces cerevisiae is known in three classes of loci: in the silent mating-type loci HML and HMR, in subtelomeric regions, and in the highly repetitive rDNA locus, which resides in the nucleolus. rDNA silencing differs markedly from the other two classes of silencing in that it requires a DNA-associated protein complex termed RENT. The Net1 protein, a central component of RENT, is required for nucleolar integrity and the control of exit from mitosis. Another RENT component is the NAD(+)-dependent histone deacetylase Sir2, which is the only silencing factor known to be shared among the three classes of silencing. Here, we investigated the role of Net1 in HMR silencing. The mutation net1-1, as well as NET1 expression from a 2micro-plasmid, restored repression at silencing-defective HMR loci. Both effects were strictly dependent on the Sir proteins. We found overexpressed Net1 protein to be directly associated with the HMR-E silencer, suggesting that Net1 could interact with silencer binding proteins and recruit other silencing factors to the silencer. In agreement with this, Net1 provided ORC-dependent, Sir1-independent silencing when artificially tethered to the silencer. In contrast, our data suggested that net1-1 acted indirectly in HMR silencing by releasing Sir2 from the nucleolus, thus shifting the internal competition for Sir2 from the silenced loci toward HMR.
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Affiliation(s)
- Daniela Kasulke
- Max-Planck-Institute for Molecular Genetics, 14195 Berlin, Germany
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17
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Robyr D, Suka Y, Xenarios I, Kurdistani SK, Wang A, Suka N, Grunstein M. Microarray deacetylation maps determine genome-wide functions for yeast histone deacetylases. Cell 2002; 109:437-46. [PMID: 12086601 DOI: 10.1016/s0092-8674(02)00746-8] [Citation(s) in RCA: 346] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Yeast contains a family of five related histone deacetylases (HDACs) whose functions are known at few genes. Therefore, we used chromatin immunoprecipitation and intergenic microarrays to generate genome-wide HDAC enzyme activity maps. Rpd3 and Hda1 deacetylate mainly distinct promoters and gene classes where they are recruited largely by novel mechanisms. Hda1 also deacetylates subtelomeric domains containing normally repressed genes that are used instead for gluconeogenesis, growth on carbon sources other than glucose, and adverse growth conditions. These domains have certain features of heterochromatin but are distinct from subtelomeric heterochromatin repressed by the deacetylase Sir2. Finally, Hos1/Hos3 and Hos2 preferentially affect ribosomal DNA and ribosomal protein genes, respectively. Thus, acetylation microarrays uncover the "division of labor" for yeast histone deacetylases.
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Affiliation(s)
- Daniel Robyr
- Department of Biological Chemistry, UCLA School of Medicine and the Molecular Biology Institute, Boyer Hall, 90095, USA
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18
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Verdone L, Wu J, Riper KV, Kacherovsky N, Vogelauer M, Young ET, Grunstein M, Mauro ED, Caserta M. Hyperacetylation of chromatin at the ADH2 promoter allows Adr1 to bind in repressed conditions. EMBO J 2002; 21:1101-11. [PMID: 11867538 PMCID: PMC125900 DOI: 10.1093/emboj/21.5.1101] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
We report that in vivo increased acetylation of the repressed Saccharomyces cerevisiae ADH2 promoter chromatin, as obtained by disrupting the genes for the two deacetylases HDA1 and RPD3, destabilizes the structure of the TATA box-containing nucleosome. This acetylation-dependent chromatin remodeling is not sufficient to allow the binding of the TATA box-binding protein, but facilitates the recruitment of the transcriptional activator Adr1 and induces faster kinetics of mRNA accumulation when the cells are shifted to derepressing conditions.
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Affiliation(s)
- Loredana Verdone
- Fondazione Istituto Pasteur-Fondazione Cenci Bolognetti and Centro di Studio per gli Acidi Nucleici, CNR, c/o Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, I-00185 Rome, Italy, Department of Biological Chemistry, UCLA School of Medicine and Molecular Biology Institute, University of California, Los Angeles, CA 90095 and Department of Biochemistry, Box 357350, University of Washington, Seattle, WA 98195-7350, USA Corresponding author e-mail:
| | - Jiansheng Wu
- Fondazione Istituto Pasteur-Fondazione Cenci Bolognetti and Centro di Studio per gli Acidi Nucleici, CNR, c/o Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, I-00185 Rome, Italy, Department of Biological Chemistry, UCLA School of Medicine and Molecular Biology Institute, University of California, Los Angeles, CA 90095 and Department of Biochemistry, Box 357350, University of Washington, Seattle, WA 98195-7350, USA Corresponding author e-mail:
| | - Kristen van Riper
- Fondazione Istituto Pasteur-Fondazione Cenci Bolognetti and Centro di Studio per gli Acidi Nucleici, CNR, c/o Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, I-00185 Rome, Italy, Department of Biological Chemistry, UCLA School of Medicine and Molecular Biology Institute, University of California, Los Angeles, CA 90095 and Department of Biochemistry, Box 357350, University of Washington, Seattle, WA 98195-7350, USA Corresponding author e-mail:
| | - Nataly Kacherovsky
- Fondazione Istituto Pasteur-Fondazione Cenci Bolognetti and Centro di Studio per gli Acidi Nucleici, CNR, c/o Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, I-00185 Rome, Italy, Department of Biological Chemistry, UCLA School of Medicine and Molecular Biology Institute, University of California, Los Angeles, CA 90095 and Department of Biochemistry, Box 357350, University of Washington, Seattle, WA 98195-7350, USA Corresponding author e-mail:
| | - Maria Vogelauer
- Fondazione Istituto Pasteur-Fondazione Cenci Bolognetti and Centro di Studio per gli Acidi Nucleici, CNR, c/o Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, I-00185 Rome, Italy, Department of Biological Chemistry, UCLA School of Medicine and Molecular Biology Institute, University of California, Los Angeles, CA 90095 and Department of Biochemistry, Box 357350, University of Washington, Seattle, WA 98195-7350, USA Corresponding author e-mail:
| | - Elton T. Young
- Fondazione Istituto Pasteur-Fondazione Cenci Bolognetti and Centro di Studio per gli Acidi Nucleici, CNR, c/o Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, I-00185 Rome, Italy, Department of Biological Chemistry, UCLA School of Medicine and Molecular Biology Institute, University of California, Los Angeles, CA 90095 and Department of Biochemistry, Box 357350, University of Washington, Seattle, WA 98195-7350, USA Corresponding author e-mail:
| | - Michael Grunstein
- Fondazione Istituto Pasteur-Fondazione Cenci Bolognetti and Centro di Studio per gli Acidi Nucleici, CNR, c/o Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, I-00185 Rome, Italy, Department of Biological Chemistry, UCLA School of Medicine and Molecular Biology Institute, University of California, Los Angeles, CA 90095 and Department of Biochemistry, Box 357350, University of Washington, Seattle, WA 98195-7350, USA Corresponding author e-mail:
| | - Ernesto Di Mauro
- Fondazione Istituto Pasteur-Fondazione Cenci Bolognetti and Centro di Studio per gli Acidi Nucleici, CNR, c/o Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, I-00185 Rome, Italy, Department of Biological Chemistry, UCLA School of Medicine and Molecular Biology Institute, University of California, Los Angeles, CA 90095 and Department of Biochemistry, Box 357350, University of Washington, Seattle, WA 98195-7350, USA Corresponding author e-mail:
| | - Micaela Caserta
- Fondazione Istituto Pasteur-Fondazione Cenci Bolognetti and Centro di Studio per gli Acidi Nucleici, CNR, c/o Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, I-00185 Rome, Italy, Department of Biological Chemistry, UCLA School of Medicine and Molecular Biology Institute, University of California, Los Angeles, CA 90095 and Department of Biochemistry, Box 357350, University of Washington, Seattle, WA 98195-7350, USA Corresponding author e-mail:
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19
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Tham WH, Zakian VA. Transcriptional silencing at Saccharomyces telomeres: implications for other organisms. Oncogene 2002; 21:512-21. [PMID: 11850776 DOI: 10.1038/sj.onc.1205078] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Telomeres are the natural ends of eukaryotic chromosomes. In most organisms, telomeres consist of simple, repeated DNA with the strand running 5' to 3' towards the end of the chromosome being rich in G residues. In cases where the very end of the chromosome has been examined, the G-strand is extended to form a short, single stranded tail. The chromatin structure of telomeric regions often has features that distinguish them from other parts of the genome. Because telomeres protect chromosome ends from degradation and end-to-end fusions and prevent the loss of terminal DNA by serving as a substrate for telomerase, they are essential for the stable maintenance of eukaryotic chromosomes. In addition to their essential functions, telomeres in diverse organisms are specialized sites for gene expression. Transcription of genes located next to telomeres is repressed, a phenomenon termed telomere position effect (TPE). TPE is best characterized in the yeast Saccharomyces cerevisiae. This article will focus on the silencing properties of Saccharomyces telomeres and end with speculation on the role of TPE in yeasts and other organisms.
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Affiliation(s)
- Wai-Hong Tham
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, NJ 08544, USA
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20
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Moretti P, Shore D. Multiple interactions in Sir protein recruitment by Rap1p at silencers and telomeres in yeast. Mol Cell Biol 2001; 21:8082-94. [PMID: 11689698 PMCID: PMC99974 DOI: 10.1128/mcb.21.23.8082-8094.2001] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2001] [Accepted: 08/28/2001] [Indexed: 12/29/2022] Open
Abstract
Initiation of transcriptional silencing at mating type loci and telomeres in Saccharomyces cerevisiae requires 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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Affiliation(s)
- P Moretti
- Department of Microbiology, College of Physicians & Surgeons of Columbia University, New York, New York 10032, USA
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21
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Abstract
Histone acetyltransferases and deacetylases can be targeted to promoters to activate or repress genes. For example, the histone acetyltransferase GCN5 is part of a yeast multiprotein complex that is recruited by the DNA-binding activator protein GCN4 (refs 1-3). The histone deacetylase RPD3 complex is recruited to DNA by the repressor UME6 (refs 4, 5); similar mechanisms exist in other eukaryotes. However, deletion of RPD3 also increases expression of the PHO5 gene that is repressed by nucleosomes, and regulated by GCN5 (ref. 10) but not by UME6. We have determined whether acetylation and deacetylation are promoter specific at PHO5, by using antibodies against acetylated lysine residues and chromatin immunoprecipitation to examine the acetylation state of a 4.25-kilobase region surrounding the PHO5 gene. Here we show that this region is acetylated extensively by ESA1 and GCN5 and deacetylated by HDA1 and RPD3, and that widespread histone modification affects three separate chromosomal regions examined, which total 22kb. Our data indicate that targeted modification occurs in a background of global acetylation and deacetylation that not only reduces basal transcription, but also allows a rapid return to the initial state of acetylation when targeting is removed.
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Affiliation(s)
- M Vogelauer
- Department of Biological Chemistry, UCLA School of Medicine and the Molecular Biology Institute, University of California, Los Angeles 90095, USA
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22
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Zhang Z, Shibahara K, Stillman B. PCNA connects DNA replication to epigenetic inheritance in yeast. Nature 2000; 408:221-5. [PMID: 11089978 DOI: 10.1038/35041601] [Citation(s) in RCA: 212] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Formation of a heterochromatin-like structure results in transcriptional silencing at the HM mating-type loci and telomeres in Saccharomyces cerevisiae. Once formed, such epigenetically determined structures are inherited for many mitotic divisions. Here we show that mutations in the proliferating cell nuclear antigen (PCNA), an essential component at the DNA replication fork, reduced repression of genes near a telomere and at the silent mating-typelocus, HMR. The pol30-8 mutant displayed coexistence of both repressed (pink) and de-repressed (white) cells within a single colony when assayed with the ADE2 gene inserted at HMR. Unlike pol30-8, the pol30-6 and pol30-79 mutants partially reduced gene silencing at telomeres and the HMR and synergistically decreased silencing in cells lacking chromatin assembly factor 1 (CAF-1). All silencing defective mutants showed reduced binding to CAF-1 in vitro and altered chromatin association of the CAF-1 large subunit in vivo. Thus, PCNA participates in inheritance of both DNA and epigenetic chromatin structures during the S phase of the cell cycle, the latter by at least two mechanisms.
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Affiliation(s)
- Z Zhang
- Cold Spring Harbor Laboratory, New York 11724, USA
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23
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Longhese MP, Paciotti V, Neecke H, Lucchini G. Checkpoint proteins influence telomeric silencing and length maintenance in budding yeast. Genetics 2000; 155:1577-91. [PMID: 10924458 PMCID: PMC1461196 DOI: 10.1093/genetics/155.4.1577] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
A complex network of surveillance mechanisms, called checkpoints, interrupts cell cycle progression when damage to the genome is detected or when cells fail to complete DNA replication, thus ensuring genetic integrity. In budding yeast, components of the DNA damage checkpoint regulatory network include the RAD9, RAD17, RAD24, MEC3, DDC1, RAD53, and MEC1 genes that are proposed to be involved in different aspects of DNA metabolism. We provide evidence that some DNA damage checkpoint components play a role in maintaining telomere integrity. In fact, rad53 mutants specifically enhance repression of telomere-proximal transcription via the Sir-mediated pathway, suggesting that Rad53 might be required for proper chromatin structure at telomeres. Moreover, Rad53, Mec1, Ddc1, and Rad17 are necessary for telomere length maintenance, since mutations in all of these genes cause a decrease in telomere size. The telomeric shortening in rad53 and mec1 mutants is further enhanced in the absence of SIR genes, suggesting that Rad53/Mec1 and Sir proteins contribute to chromosome end protection by different pathways. The finding that telomere shortening, but not increased telomeric repression of gene expression in rad53 mutants, can be suppressed by increasing dNTP synthetic capacity in these strains suggests that transcriptional silencing and telomere integrity involve separable functions of Rad53.
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Affiliation(s)
- M P Longhese
- Dipartimento di Biotecnologie e Bioscienze, Università degli Studi di Milano-Bicocca, 20126 Milan, Italy.
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24
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Hollenhorst PC, Bose ME, Mielke MR, Müller U, Fox CA. Forkhead genes in transcriptional silencing, cell morphology and the cell cycle. Overlapping and distinct functions for FKH1 and FKH2 in Saccharomyces cerevisiae. Genetics 2000; 154:1533-48. [PMID: 10747051 PMCID: PMC1461039 DOI: 10.1093/genetics/154.4.1533] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The SIR1 gene is one of four specialized genes in Saccharomyces cerevisiae required for repressing transcription at the silent mating-type cassettes, HMLalpha and HMRa, by a mechanism known as silencing. Silencing requires the assembly of a specialized chromatin structure analogous to heterochromatin. FKH1 was isolated as a gene that, when expressed in multiple copies, could substitute for the function of SIR1 in silencing HMRa. FKH1 (Forkhead Homologue One) was named for its homology to the forkhead family of eukaryotic transcription factors classified on the basis of a conserved DNA binding domain. Deletion of FKH1 caused a defect in silencing HMRa, indicating that FKH1 has a positive role in silencing. Significantly, deletion of both FKH1 and its closest homologue in yeast, FKH2, caused a form of yeast pseudohyphal growth, indicating that the two genes have redundant functions in controlling yeast cell morphology. By several criteria, fkh1Delta fkh2Delta-induced pseudohyphal growth was distinct from the nutritionally induced form of pseudohyphal growth observed in some strains of S. cerevisiae. Although FKH2 is redundant with FKH1 in controlling pseudohyphal growth, the two genes have different functions in silencing HMRa. High-copy expression of CLB2, a G2/M-phase cyclin, prevented fkh1Delta fkh2Delta-induced pseudohyphal growth and modulated some of the fkhDelta-induced silencing phenotypes. Interestingly, deletions in either FKH1 or FKH2 alone caused subtle but opposite effects on cell-cycle progression and CLB2 mRNA expression, consistent with a role for each of these genes in modulating the cell cycle and having opposing effects on silencing. The differences between Fkh1p and Fkh2p in vivo were not attributable to differences in their DNA binding domains.
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Affiliation(s)
- P C Hollenhorst
- Department of Biomolecular Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
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25
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Ehrenhofer-Murray AE, Kamakaka RT, Rine J. A role for the replication proteins PCNA, RF-C, polymerase epsilon and Cdc45 in transcriptional silencing in Saccharomyces cerevisiae. Genetics 1999; 153:1171-82. [PMID: 10545450 PMCID: PMC1460823 DOI: 10.1093/genetics/153.3.1171] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Transcriptional silencing in the budding yeast Saccharomyces cerevisiae may be linked to DNA replication and cell cycle progression. In this study, we have surveyed the effect of 41 mutations in genes with a role in replication, the cell cycle, and DNA repair on silencing at HMR. Mutations in PCNA (POL30), RF-C (CDC44), polymerase epsilon (POL2, DPB2, DPB11), and CDC45 were found to restore silencing at a mutant HMR silencer allele that was still a chromosomal origin of replication. Replication timing experiments indicated that the mutant HMR locus was replicated late in S-phase, at the same time as wild-type HMR. Restoration of silencing by PCNA and CDC45 mutations required the origin recognition complex binding site of the HMR-E silencer. Several models for the precise role of these replication proteins in silencing are discussed.
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Affiliation(s)
- A E Ehrenhofer-Murray
- Department of Molecular and Cell Biology, Division of Genetics, University of California, Berkeley, California 94720, USA
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26
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Carmen AA, Griffin PR, Calaycay JR, Rundlett SE, Suka Y, Grunstein M. Yeast HOS3 forms a novel trichostatin A-insensitive homodimer with intrinsic histone deacetylase activity. Proc Natl Acad Sci U S A 1999; 96:12356-61. [PMID: 10535926 PMCID: PMC22921 DOI: 10.1073/pnas.96.22.12356] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Histone deacetylases such as human HDAC1 and yeast RPD3 are trichostatin A (TSA)-sensitive enzymes that are members of large, multiprotein complexes. These contain specialized subunits that help target the catalytic protein to histones at the appropriate DNA regulatory element, where the enzyme represses transcription. To date, no deacetylase catalytic subunits have been shown to have intrinsic activity, suggesting that noncatalytic subunits of the deacetylase complex are required for their enzymatic function. In this paper we describe a novel yeast histone deacetylase HOS3 that is relatively insensitive to the histone deacetylase inhibitor TSA, forms a homodimer when expressed ectopically both in yeast and Escherichia coli, and has intrinsic activity when produced in the bacterium. Most HOS3 protein can be found associated with a larger complex in partially purified yeast nuclear extracts, arguing that the HOS3 homodimer may be dissociated from a very large nuclear structure during purification. We also demonstrate, using a combination of mass spectrometry, tandem mass spectrometry, and proteolytic digestion, that recombinant HOS3 has a distinct specificity in vitro for histone H4 sites K5 and K8, H3 sites K14 and K23, H2A site K7, and H2B site K11. We propose that while factors that interact with HOS3 may sequester the catalytic subunit at specific cellular sites, they are not required for HOS3 histone deacetylase activity.
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Affiliation(s)
- A A Carmen
- Department of Biological Chemistry, UCLA School of Medicine, University of California, Los Angeles, CA 90095, USA
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27
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Abstract
Certain nickel compounds including crystalline nickel sulfide (NiS) and subsulfide (Ni3S2) are potent human and animal carcinogens. In Chinese hamster embryo cells, an X-linked senescence gene was inactivated following nickel-induced DNA methylation. Nickel also induced the inactivation of the gpt reporter gene by chromatin condensation and a DNA methylation process in a transgenic gpt+ Chinese hamster cell line (G12), which is located near a heterochromatic region. To determine if nickel can cause gene silencing independently of DNA methylation, based only on the induction of changes in chromatin structure, we measured its effect on gene silencing in Saccharomyces cerevisiae. Growth of yeast in the presence of nickel chloride repressed a telomeric marker gene (URA3) and resulted in a stable epigenetic switch. This phenomenon was dependent on the number of cell doubling prior to selection and also on the distance of the marker gene from the end of the chromosome. The level of TPE (telomeric position effect) increased linearly with elevations of nickel concentration. Addition of magnesium inhibited this effect, but magnesium did not silence the reporter gene by itself. The level of silencing was also assessed following treatment with other transition metals: cobalt, copper and cadmium. In the sublethal range, cobalt induced similar effects as nickel, while copper and cadmium did not change the basal level of gene expression. Silencing by copper and cadmium were evident only at concentrations of those metals where the viability was very low.
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Affiliation(s)
- L Broday
- Department of Environmental Medicine, New York University School of Medicine, 550 First Avenue, New York, NY 10016, USA
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28
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Ray A, Runge KW. The yeast telomere length counting machinery is sensitive to sequences at the telomere-nontelomere junction. Mol Cell Biol 1999; 19:31-45. [PMID: 9858529 PMCID: PMC83863 DOI: 10.1128/mcb.19.1.31] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Saccharomyces cerevisiae telomeres consist of a continuous 325 +/- 75-bp tract of the heterogeneous repeat TG1-3 which contains irregularly spaced, high-affinity sites for the protein Rap1p. Yeast cells monitor or count the number of telomeric Rap1p molecules in a negative feedback mechanism which modulates telomere length. To investigate the mechanism by which Rap1p molecules are counted, the continuous telomeric TG1-3 sequences were divided into internal TG1-3 sequences and a terminal tract separated by nontelomeric spacers of different lengths. While all of the internal sequences were counted as part of the terminal tract across a 38-bp spacer, a 138-bp disruption completely prevented the internal TG1-3 sequences from being considered part of the telomere and defined the terminal tract as a discrete entity separate from the subtelomeric sequences. We also used regularly spaced arrays of six Rap1p sites internal to the terminal TG1-3 repeats to show that each Rap1p molecule was counted as about 19 bp of TG1-3 in vivo and that cells could count Rap1p molecules with different spacings between tandem sites. As previous in vitro experiments had shown that telomeric Rap1p sites occur about once every 18 bp, all Rap1p molecules at the junction of telomeric and nontelomeric chromatin (the telomere-nontelomere junction) must participate in telomere length measurement. The conserved arrangement of these six Rap1p molecules at the telomere-nontelomere junction in independent transformants also caused the elongated TG1-3 tracts to be maintained at nearly identical lengths, showing that sequences at the telomere-nontelomere junction had an effect on length regulation. These results can be explained by a model in which telomeres beyond a threshold length form a folded structure that links the chromosome terminus to the telomere-nontelomere junction and prevents telomere elongation.
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Affiliation(s)
- A Ray
- Department of Molecular Biology, The Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA
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29
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Singer MS, Kahana A, Wolf AJ, Meisinger LL, Peterson SE, Goggin C, Mahowald M, Gottschling DE. Identification of high-copy disruptors of telomeric silencing in Saccharomyces cerevisiae. Genetics 1998; 150:613-32. [PMID: 9755194 PMCID: PMC1460361 DOI: 10.1093/genetics/150.2.613] [Citation(s) in RCA: 367] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The ends of chromosomes in Saccharomyces cerevisiae initiate a repressive chromatin structure that spreads internally and inhibits the transcription of nearby genes, a phenomenon termed telomeric silencing. To investigate the molecular basis of this process, we carried out a genetic screen to identify genes whose overexpression disrupts telomeric silencing. We thus isolated 10 DOT genes (disruptor of telomeric silencing). Among these were genes encoding chromatin component Sir4p, DNA helicase Dna2p, ribosomal protein L32, and two proteins of unknown function, Asf1p and Ifh1p. The collection also included genes that had not previously been identified: DOT1, DOT4, DOT5, DOT6, and TLC1, which encodes the RNA template component of telomerase. With the exception of TLC1, all these genes, particularly DOT1 and DOT4, also reduced silencing at other repressed loci (HM loci and rDNA) when overexpressed. Moreover, deletion of the latter two genes weakened silencing as well, suggesting that DOT1 and DOT4 normally play important roles in gene repression. DOT1 deletion also affected telomere tract length. The function of Dot1p is not known. The sequence of Dot4p suggests that it is a ubiquitin-processing protease. Taken together, the DOT genes include both components and regulators of silent chromatin.
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Affiliation(s)
- M S Singer
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637, USA
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30
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Rundlett SE, Carmen AA, Suka N, Turner BM, Grunstein M. Transcriptional repression by UME6 involves deacetylation of lysine 5 of histone H4 by RPD3. Nature 1998; 392:831-5. [PMID: 9572144 DOI: 10.1038/33952] [Citation(s) in RCA: 346] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The histone deacetylase RPD3 can be targeted to certain genes through its interaction with DNA-binding regulatory proteins. RPD3 can then repress gene transcription. In the yeast Saccharomyces cerevisiae, association of RPD3 with the transcriptional repressors SIN3 and UME6 results in repression of reporter genes containing the UME6-binding site. RPD3 can deacetylate all histone H4 acetylation sites in cell extracts. However, it is unknown how H4 proteins located at genes near UME6-binding sites are affected, nor whether the effect of RPD3 is localized to the promoter regions. Here we study the mechanism by which RPD3 represses gene activity by examining the acetylation state of histone proteins at UME6-regulated genes. We used antibodies specific for individual acetylation sites in H4 to immunoprecipitate chromatin fragments. A deletion of RPD3 or SIN3, but not of the related histone-deacetylase gene HDA1, results in increased acetylation of the lysine 5 residue of H4 in the promoters of the UME6-regulated INO1, IME2 and SPO13 genes. As increased acetylation of this residue is not merely a consequence of gene transcription, acetylation of this site may be essential for regulating gene activity.
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Affiliation(s)
- S E Rundlett
- Department of Biological Chemistry, UCLA School of Medicine, Los Angeles, California 90095, USA
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31
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Abstract
Extensive regions of chromosomes can be transcriptionally repressed through silencing mechanisms mediated by complex chromatin structures. One of the most refined molecular portraits of silenced chromatin comes from studies of the silent mating-type loci and telomeres of S. cerevisiae. In this budding yeast, the Sir3p silent information regulator emerges as a critically important silencing component that interacts with nucleosomes and other silencing proteins. Not only is it essential for silencing, but Sir3p is also capable of spreading silenced chromatin when its dosage is increased. Sir3p is a target of mitogen-activated protein (MAP) kinase cascade regulation and has significant similarity to the Orc1p subunit of the DNA replication origin recognition complex. Thus, in concert with other silencing proteins, Sir3p appears poised to respond to cellular signals and reprogram silencing through replication-associated assembly of repressive chromatin structures.
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Affiliation(s)
- E M Stone
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder 80309-0347, USA
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32
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Huang H, Kahana A, Gottschling DE, Prakash L, Liebman SW. The ubiquitin-conjugating enzyme Rad6 (Ubc2) is required for silencing in Saccharomyces cerevisiae. Mol Cell Biol 1997; 17:6693-9. [PMID: 9343433 PMCID: PMC232523 DOI: 10.1128/mcb.17.11.6693] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
It has been previously shown that genes transcribed by RNA polymerase II (RNAP II) are subject to position effect variegation when located near yeast telomeres. This telomere position effect requires a number of gene products that are also required for silencing at the HML and HMR loci. Here, we show that a null mutation of the DNA repair gene RAD6 reduces silencing of the HM loci and lowers the mating efficiency of MATa strains. Likewise, rad6-delta reduces silencing of the telomere-located RNAP II-transcribed genes URA3 and ADE2. We also show that the RNAP III-transcribed tyrosyl tRNA gene, SUP4-o, is subject to position effect variegation when located near a telomere and that this silencing requires the RAD6 and SIR genes. Neither of the two known Rad6 binding factors, Rad18 and Ubr1, is required for telomeric silencing. Since Ubrl is the recognition component of the N-end rule-dependent protein degradation pathway, this suggests that N-end rule-dependent protein degradation is not involved in telomeric silencing. Telomeric silencing requires the amino terminus of Rad6. Two rad6 point mutations, rad6(C88A) and rad6(C88S), which are defective in ubiquitin-conjugating activity fail to complement the silencing defect, indicating that the ubiquitin-conjugating activity of RAD6 is essential for full telomeric silencing.
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Affiliation(s)
- H Huang
- Department of Biological Sciences, University of Illinois at Chicago, 60607, USA
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33
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Abstract
Transcriptional silencing is the most well-studied epigenetic phenomenon in yeast. In Saccharomyces cerevisiae, silencing has recently been found at previously unidentified loci. In addition to the silent mating-type loci and telomeres, genes within the ribosomal DNA and, perhaps, at undefined aging loci are silenced. Efficiency of silencing at different loci varies and is affected by competition between the loci and by the involvement of different factors in distinct protein complexes. The recent discovery of conserved gene families encoding proteins related to modulators of acetylation and deacetylation suggests mechanisms for differential regulation of silencing at known loci and the existence of additional, as yet undiscovered, silenced loci.
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Affiliation(s)
- J M Sherman
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder 80309-0347, USA.
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34
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Abstract
Whether or not genes are in an active or a repressed state in a cell depends on the relative effect of gene silencers and locus control regions (LCRs). Here, we suggest that these elements act as binary switches; the state that prevails (activated or repressed) probably depends on a competition between protein complex formation and the stability of the complexes formed at either of the two elements.
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Affiliation(s)
- R T Kamakaka
- Laboratory of Molecular Embryology, NICHD, Bethesda, MD 20892, USA
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35
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Enomoto S, McCune-Zierath PD, Gerami-Nejad M, Sanders MA, Berman J. RLF2, a subunit of yeast chromatin assembly factor-I, is required for telomeric chromatin function in vivo. Genes Dev 1997; 11:358-70. [PMID: 9030688 DOI: 10.1101/gad.11.3.358] [Citation(s) in RCA: 131] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
In the yeast Saccharomyces cerevisiae, telomere repeat DNA is assembled into a specialized heterochromatin-like complex that silences the transcription of adjacent genes. The general DNA-binding protein Rap1p binds telomere DNA repeats, contributes to telomere length control and to telomeric silencing, and is a major component of telomeric chromatin. We identified Rap1p localization factor 2 (RLF2) in a screen for genes that alleviate antagonism between telomere and centromere sequences on plasmids. In rlf2 mutants, telomeric chromatin is perturbed: Telomeric silencing is reduced and Rap1p localization is altered. In wild-type cells, Rap1p and telomeres localize to bright perinuclear foci. In rlf2 strains, the number of Rap1p foci is increased, Rap1p staining is more diffuse throughout the nucleus, Rap1p foci are distributed in a much broader perinuclear domain, and nuclear volume is 50% larger. Despite the altered distribution of Rap1p in rlf2 mutant cells, fluorescence in situ hybridization to subtelomeric repeats shows that the distribution of telomeric DNA is similar in wild-type and mutant cells. Thus in rlf2 mutant cells, the distribution of Rap1p does not reflect the distribution of telomeric DNA. RLF2 encodes a highly charged coiled-coil protein that has significant similarity to the p150 subunit of human chromatin assembly factor-I(hCAF-I), a complex that is required for the DNA replication-dependent assembly of nucleosomes from newly synthesized histones in vitro. Furthermore, RLF2 is identical to CAC1, a subunit of yeast chromatin assembly factor-I (yCAF-I) which assembles nucleosomes in vitro. In wild-type cells, epitope-tagged Rlf2p expressed from the GAL10 promoter localizes to the nucleus with a pattern distinct from that of Rap1p, suggesting that Rlf2p is not a component of telomeric chromatin. This study provides evidence that yCAF-I is required for the function and organization of telomeric chromatin in vivo. We propose that Rlf2p facilitates the efficient and timely assembly of histones into telomeric chromatin.
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Affiliation(s)
- S Enomoto
- Department of Plant Biology, University of Minnesota, St. Paul 55108, USA
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Rundlett SE, Carmen AA, Kobayashi R, Bavykin S, Turner BM, Grunstein M. HDA1 and RPD3 are members of distinct yeast histone deacetylase complexes that regulate silencing and transcription. Proc Natl Acad Sci U S A 1996; 93:14503-8. [PMID: 8962081 PMCID: PMC26162 DOI: 10.1073/pnas.93.25.14503] [Citation(s) in RCA: 493] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/1996] [Accepted: 09/27/1996] [Indexed: 02/03/2023] Open
Abstract
Increased histone acetylation has been correlated with increased transcription, and regions of heterochromatin are generally hypoacetylated. In investigating the cause-and-effect relationship between histone acetylation and gene activity, we have characterized two yeast histone deacetylase complexes. Histone deacetylase-A (HDA) is an approximately 350-kDa complex that is highly sensitive to the deacetylase inhibitor trichostatin A. Histone deacetylase-B (HDB) is an approximately 600-kDa complex that is much less sensitive to trichostatin A. The HDA1 protein (a subunit of the HDA activity) shares sequence similarity to RPD3, a factor required for optimal transcription of certain yeast genes. RPD3 is associated with the HDB activity. HDA1 also shares similarity to three new open reading frames in yeast, designated HOS1, HOS2, and HOS3. We find that both hda1 and rpd3 deletions increase acetylation levels in vivo at all sites examined in both core histones H3 and H4, with rpd3 deletions having a greater impact on histone H4 lysine positions 5 and 12. Surprisingly, both hda1 and rpd3 deletions increase repression at telomeric loci, which resemble heterochromatin with rpd3 having a greater effect. In addition, rpd3 deletions retard full induction of the PHO5 promoter fused to the reporter lacZ. These data demonstrate that histone acetylation state has a role in regulating both heterochromatic silencing and regulated gene expression.
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Affiliation(s)
- S E Rundlett
- Department of Biological Chemistry, University of California School of Medicine, Los Angeles 90095, USA
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Henchoz S, De Rubertis F, Pauli D, Spierer P. The dose of a putative ubiquitin-specific protease affects position-effect variegation in Drosophila melanogaster. Mol Cell Biol 1996; 16:5717-25. [PMID: 8816485 PMCID: PMC231572 DOI: 10.1128/mcb.16.10.5717] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
A dominant insertional P-element mutation enhances position-effect variegation in Drosophila melanogaster. The mutation is homozygous, viable, and fertile and maps at 64E on the third chromosome. The corresponding gene was cloned by transposon tagging. Insertion of the transposon upstream of the open reading frame correlates with a strong reduction of transcript level. A transgene was constructed with the cDNA and found to have the effect opposite from that of the mutation, namely, to suppress variegation. Sequencing of the cDNA reveals a large open reading frame encoding a putative ubiquitin-specific protease (Ubp). Ubiquitin marks various proteins, frequently for proteasome-dependent degradation. Ubps can cleave the ubiquitin part from these proteins. We discuss the link established here between a deubiquitinating enzyme and epigenetic silencing processes.
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MESH Headings
- Amino Acid Sequence
- Animals
- Animals, Genetically Modified
- Base Sequence
- Chromosome Mapping
- Crosses, Genetic
- Drosophila melanogaster/enzymology
- Drosophila melanogaster/genetics
- Embryo, Nonmammalian
- Endopeptidases/genetics
- Endopeptidases/metabolism
- Female
- Gene Expression Regulation, Developmental
- Gene Expression Regulation, Enzymologic
- Genes, Homeobox
- Genes, Insect
- Homozygote
- Male
- Molecular Sequence Data
- Mutagenesis, Insertional
- Open Reading Frames
- Pigmentation
- Recombination, Genetic
- Restriction Mapping
- Sequence Homology, Amino Acid
- Transcription, Genetic
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Affiliation(s)
- S Henchoz
- Department of Zoology and Animal Biology, University of Geneva, Switzerland
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Seum C, Spierer A, Pauli D, Szidonya J, Reuter G, Spierer P. Position-effect variegation in Drosophila depends on dose of the gene encoding the E2F transcriptional activator and cell cycle regulator. Development 1996; 122:1949-56. [PMID: 8674433 DOI: 10.1242/dev.122.6.1949] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A dominant mutation due to the insertion of a P-element at 93E on the third chromosome of Drosophila melanogaster enhances position-effect variegation. The corresponding gene was cloned by transposon tagging and the sequence of the transcript revealed that it corresponds to the gene encoding the transcriptional activator and cell cycle regulator dE2F. The transposon-tagged allele is homozygous viable, and the insertion of the transposon in an intron correlates with a strong reduction in the amount of transcript. A homozygous lethal null allele was found to behave as a strong enhancer when heterozygous. Overexpression of the gene in transgenic flies has the opposite effect of suppressing variegation. A link is established here, and discussed, between the dose of a transcriptional activator, which controls the cell cycle, and epigenetic silencing of chromosomal domains in Drosophila.
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Affiliation(s)
- C Seum
- Department of Zoology and Animal Biology, University of Geneva, Switzerland
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Abstract
Silencing in Saccharomyces cerevisiae is a form of transcriptional repression that involves the assembly of a specialized and heritable structure of chromatin. The HML and HMR loci, which contain copies of the genes found at the yeast mating-type locus, are silenced, as are telomeres. These examples share several features which are also found in position-effect variegation in flies and X-chromosome inactivation and genomic imprinting in mammals. Silenced chromatin is confined to a few special domains of the yeast genome, and active genes inserted into these domains become silenced. Molecular and genetic evidence has suggested that the establishment of silenced chromatin requires some S phase specific function. Recent experiments indicate that the assembly and maintenance of silenced chromatin can also be influenced at other phases of the cell cycle.
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Affiliation(s)
- C A Fox
- Department of Molecular and Cell Biology, University of California, Berkeley 94720, USA.
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Brachmann CB, Sherman JM, Devine SE, Cameron EE, Pillus L, Boeke JD. The SIR2 gene family, conserved from bacteria to humans, functions in silencing, cell cycle progression, and chromosome stability. Genes Dev 1995; 9:2888-902. [PMID: 7498786 DOI: 10.1101/gad.9.23.2888] [Citation(s) in RCA: 475] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Genomic silencing is a fundamental mechanism of transcriptional regulation, yet little is known about conserved mechanisms of silencing. We report here the discovery of four Saccharomyces cerevisiae homologs of the SIR2 silencing gene (HSTs), as well as conservation of this gene family from bacteria to mammals. At least three HST genes can function in silencing; HST1 overexpression restores transcriptional silencing to a sir2 mutant and hst3 hst4 double mutants are defective in telomeric silencing. In addition, HST3 and HST4 together contribute to proper cell cycle progression, radiation resistance, and genomic stability, establishing new connections between silencing and these fundamental cellular processes.
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Affiliation(s)
- C B Brachmann
- Department of Molecular Biology and Genetics, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA
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Sussel L, Vannier D, Shore D. Suppressors of defective silencing in yeast: effects on transcriptional repression at the HMR locus, cell growth and telomere structure. Genetics 1995; 141:873-88. [PMID: 8582633 PMCID: PMC1206851 DOI: 10.1093/genetics/141.3.873] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
To identify factors that affect transcriptional silencing at the HMR mating-type locus in yeast, we characterized a set of extragenic suppressor mutations that restore metastable repression in cells containing both a mutant silencer-binding protein (rap1s) and a mutated silencer element (hmr delta A). A total of 57 suppressors comprising 21 different complementation groups was identified. This report describes a detailed genetic analysis of these suppressors of defective silencing (sds) mutants. The sds mutants fall into several distinct categories based on secondary phenotypes, such as their ability to suppress the rap1s telomere lengthening phenotype, general effects on telomere length, temperature-dependent growth defects, and the ability to bypass the requirement for cis regulatory elements at the HMR-E silencer. One particular mutant, sds4-1, strongly suppresses the rap1s silencing defect, restores telomeres to nearly wild-type length, and displays a severe growth defect at all temperatures. SDS4 mutations also suppress the silencing defect caused by mutations in the RAP1-interacting factor RIF1. We cloned the SDS4 gene and show that it is identical to GAL11(SPT13), which encodes a component of a protein complex that mediates transcriptional activation. Possible mechanism(s) of suppression by sds4 and the other sds mutations is discussed.
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Affiliation(s)
- L Sussel
- Department of Microbiology, College of Physicians & Surgeons of Columbia University, New York, New York 10032, USA
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