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Abstract
The budding yeast Saccharomyces cerevisiae has two alternative mating types designated MATa and MATα. These are distinguished by about 700 bp of unique sequences, Ya or Yα, including divergent promoter sequences and part of the open reading frames of genes that regulate mating phenotype. Homothallic budding yeast, carrying an active HO endonuclease gene, HO, can switch mating type through a recombination process known as gene conversion, in which a site-specific double-strand break (DSB) created immediately adjacent to the Y region results in replacement of the Y sequences with a copy of the opposite mating type information, which is harbored in one of two heterochromatic donor loci, HMLα or HMRa. HO gene expression is tightly regulated to ensure that only half of the cells in a lineage switch to the opposite MAT allele, thus promoting conjugation and diploid formation. Study of the silencing of these loci has provided a great deal of information about the role of the Sir2 histone deacetylase and its associated Sir3 and Sir4 proteins in creating heterochromatic regions. MAT switching has been examined in great detail to learn about the steps in homologous recombination. MAT switching is remarkably directional, with MATa recombining preferentially with HMLα and MATα using HMRa. Donor preference is controlled by a cis-acting recombination enhancer located near HML. RE is turned off in MATα cells but in MATa binds multiple copies of the Fkh1 transcription factor whose forkhead-associated phosphothreonine binding domain localizes at the DSB, bringing HML into conjunction with MATa.
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2
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Abstract
Mating type in Saccharomyces cerevisiae is determined by two nonhomologous alleles, MATa and MATα. These sequences encode regulators of the two different haploid mating types and of the diploids formed by their conjugation. Analysis of the MATa1, MATα1, and MATα2 alleles provided one of the earliest models of cell-type specification by transcriptional activators and repressors. Remarkably, homothallic yeast cells can switch their mating type as often as every generation by a highly choreographed, site-specific homologous recombination event that replaces one MAT allele with different DNA sequences encoding the opposite MAT allele. This replacement process involves the participation of two intact but unexpressed copies of mating-type information at the heterochromatic loci, HMLα and HMRa, which are located at opposite ends of the same chromosome-encoding MAT. The study of MAT switching has yielded important insights into the control of cell lineage, the silencing of gene expression, the formation of heterochromatin, and the regulation of accessibility of the donor sequences. Real-time analysis of MAT switching has provided the most detailed description of the molecular events that occur during the homologous recombinational repair of a programmed double-strand chromosome break.
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Chakraborty SA, Simpson RT, Grigoryev SA. A single heterochromatin boundary element imposes position-independent antisilencing activity in Saccharomyces cerevisiae minichromosomes. PLoS One 2011; 6:e24835. [PMID: 21949764 PMCID: PMC3174977 DOI: 10.1371/journal.pone.0024835] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2011] [Accepted: 08/22/2011] [Indexed: 11/19/2022] Open
Abstract
Chromatin boundary elements serve as cis-acting regulatory DNA signals required to protect genes from the effects of the neighboring heterochromatin. In the yeast genome, boundary elements act by establishing barriers for heterochromatin spreading and are sufficient to protect a reporter gene from transcriptional silencing when inserted between the silencer and the reporter gene. Here we dissected functional topography of silencers and boundary elements within circular minichromosomes in Saccharomyces cerevisiae. We found that both HML-E and HML-I silencers can efficiently repress the URA3 reporter on a multi-copy yeast minichromosome and we further showed that two distinct heterochromatin boundary elements STAR and TEF2-UASrpg are able to limit the heterochromatin spreading in circular minichromosomes. In surprising contrast to what had been observed in the yeast genome, we found that in minichromosomes the heterochromatin boundary elements inhibit silencing of the reporter gene even when just one boundary element is positioned at the distal end of the URA3 reporter or upstream of the silencer elements. Thus the STAR and TEF2-UASrpg boundary elements inhibit chromatin silencing through an antisilencing activity independently of their position or orientation in S. cerevisiae minichromosomes rather than by creating a position-specific barrier as seen in the genome. We propose that the circular DNA topology facilitates interactions between the boundary and silencing elements in the minichromosomes.
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Affiliation(s)
- Sangita A. Chakraborty
- Department of Biochemistry and Molecular Biology, College of Medicine, Pennsylvania State University, Milton S. Hershey Medical Center, Hershey, Pennsylvania, United States of America
- * E-mail: (SAC); (SAG)
| | - Robert T. Simpson
- Department of Biochemistry and Molecular Biology, Eberly College of Science, Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Sergei A. Grigoryev
- Department of Biochemistry and Molecular Biology, College of Medicine, Pennsylvania State University, Milton S. Hershey Medical Center, Hershey, Pennsylvania, United States of America
- * E-mail: (SAC); (SAG)
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Corepressor-directed preacetylation of histone H3 in promoter chromatin primes rapid transcriptional switching of cell-type-specific genes in yeast. Mol Cell Biol 2010; 30:3342-56. [PMID: 20439496 DOI: 10.1128/mcb.01450-09] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Switching between alternate states of gene transcription is fundamental to a multitude of cellular regulatory pathways, including those that govern differentiation. In spite of the progress in our understanding of such transitions in gene activity, a major unanswered question is how cells regulate the timing of these switches. Here, we have examined the kinetics of a transcriptional switch that accompanies the differentiation of yeast cells of one mating type into a distinct new cell type. We found that cell-type-specific genes silenced by the alpha2 repressor in the starting state are derepressed to establish the new mating-type-specific gene expression program coincident with the loss of alpha2 from promoters. This rapid derepression does not require the preloading of RNA polymerase II or a preinitiation complex but instead depends upon the Gcn5 histone acetyltransferase. Surprisingly, Gcn5-dependent acetylation of nucleosomes in the promoters of mating-type-specific genes requires the corepressor Ssn6-Tup1 even in the repressed state. Gcn5 partially acetylates the amino-terminal tails of histone H3 in repressed promoters, thereby priming them for rapid derepression upon loss of alpha2. Thus, Ssn6-Tup1 not only efficiently represses these target promoters but also functions to initiate derepression by creating a chromatin state poised for rapid activation.
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Coupling phosphate homeostasis to cell cycle-specific transcription: mitotic activation of Saccharomyces cerevisiae PHO5 by Mcm1 and Forkhead proteins. Mol Cell Biol 2009; 29:4891-905. [PMID: 19596791 DOI: 10.1128/mcb.00222-09] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Cells devote considerable resources to nutrient homeostasis, involving nutrient surveillance, acquisition, and storage at physiologically relevant concentrations. Many Saccharomyces cerevisiae transcripts coding for proteins with nutrient uptake functions exhibit peak periodic accumulation during M phase, indicating that an important aspect of nutrient homeostasis involves transcriptional regulation. Inorganic phosphate is a central macronutrient that we have previously shown oscillates inversely with mitotic activation of PHO5. The mechanism of this periodic cell cycle expression remains unknown. To date, only two sequence-specific activators, Pho4 and Pho2, were known to induce PHO5 transcription. We provide here evidence that Mcm1, a MADS-box protein, is essential for PHO5 mitotic activation. In addition, we found that cells simultaneously lacking the forkhead proteins, Fkh1 and Fkh2, exhibited a 2.5-fold decrease in PHO5 expression. The Mcm1-Fkh2 complex, first shown to transactivate genes within the CLB2 cluster that drive G(2)/M progression, also associated directly at the PHO5 promoter in a cell cycle-dependent manner in chromatin immunoprecipitation assays. Sds3, a component specific to the Rpd3L histone deacetylase complex, was also recruited to PHO5 in G(1). These findings provide (i) further mechanistic insight into PHO5 mitotic activation, (ii) demonstrate that Mcm1-Fkh2 can function combinatorially with other activators to yield late M/G(1) induction, and (iii) couple the mitotic cell cycle progression machinery to cellular phosphate homeostasis.
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6
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The Saccharomyces cerevisiae linker histone Hho1p is essential for chromatin compaction in stationary phase and is displaced by transcription. Proc Natl Acad Sci U S A 2008; 105:14838-43. [PMID: 18799740 DOI: 10.1073/pnas.0806337105] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The importance of core histones in the regulation of DNA function by chromatin is clear. However, little is known about the role of the linker histone. We investigated the role of H1 in Saccharomyces cerevisiae during extensive transcriptional reprogramming in stationary phase. Although the levels of linker histone Hho1p remained constant during growth to semiquiescence, there was a genome-wide increase in binding to chromatin. Hho1p was essential for compaction of chromatin in stationary phase, but not for general transcriptional repression. A clear, genome-wide anticorrelation was seen between the level of bound Hho1p and gene expression. Surprisingly, the rank order of gene activity was maintained even in the absence of Hho1p. Based on these findings, we suggest that linker histone Hho1p has a limited role in transcriptional regulation and that the dynamically exchanging linker histone may be evicted from chromatin by transcriptional activity.
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7
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Morohashi N, Yamamoto Y, Kuwana S, Morita W, Shindo H, Mitchell AP, Shimizu M. Effect of sequence-directed nucleosome disruption on cell-type-specific repression by alpha2/Mcm1 in the yeast genome. EUKARYOTIC CELL 2006; 5:1925-33. [PMID: 16980406 PMCID: PMC1694797 DOI: 10.1128/ec.00105-06] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In Saccharomyces cerevisiae, a-cell-specific genes are repressed in MATalpha cells by alpha2/Mcm1, acting in concert with the Ssn6-Tup1 corepressors and the Isw2 chromatin remodeling complex, and nucleosome positioning has been proposed as one mechanism of repression. However, prior studies showed that nucleosome positioning is not essential for repression by alpha2/Mcm1 in artificial reporter plasmids, and the importance of the nucleosome positioning remains questionable. We have tested the function of positioned nucleosomes through alteration of genomic chromatin at the a-cell-specific gene BAR1. We report here that a positioned nucleosome in the BAR1 promoter is disrupted in cis by the insertion of diverse DNA sequences such as poly(dA) . poly(dT) and poly(dC-dG) . poly(dC-dG), leading to inappropriate partial derepression of BAR1. Also, we show that isw2 mutation causes loss of nucleosome positioning in BAR1 in MATalpha cells as well as partial disruption of repression. Thus, nucleosome positioning is required for full repression, but loss of nucleosome positioning is not sufficient to relieve repression completely. Even though disruption of nucleosome positioning by the cis- and trans-acting modulators of chromatin has a modest effect on the level of transcription, it causes significant degradation of the alpha-mating pheromone in MATalpha cells, thereby affecting its cell type identity. Our results illustrate a useful paradigm for analysis of chromatin structural effects at genomic loci.
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Affiliation(s)
- Nobuyuki Morohashi
- Department of Chemistry, Meisei University, 2-1-1 Hodokubo, Hino, Tokyo 191-8506, Japan
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8
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Simms TA, Miller EC, Buisson NP, Jambunathan N, Donze D. The Saccharomyces cerevisiae TRT2 tRNAThr gene upstream of STE6 is a barrier to repression in MATalpha cells and exerts a potential tRNA position effect in MATa cells. Nucleic Acids Res 2004; 32:5206-13. [PMID: 15459290 PMCID: PMC521669 DOI: 10.1093/nar/gkh858] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A growing body of evidence suggests that genes transcribed by RNA polymerase III exhibit multiple functions within a chromosome. While the predominant function of these genes is the synthesis of RNA molecules, certain RNA polymerase III genes also function as genomic landmarks. Transfer RNA genes are known to exhibit extra-transcriptional activities such as directing Ty element integration, pausing of replication forks, overriding nucleosome positioning sequences, repressing neighboring genes (tRNA position effect), and acting as a barrier to the spread of repressive chromatin. This study was designed to identify other tRNA loci that may act as barriers to chromatin-mediated repression, and focused on TRT2, a tRNA(Thr) adjacent to the STE6 alpha2 operator. We show that TRT2 acts as a barrier to repression, protecting the upstream CBT1 gene from the influence of the STE6 alpha2 operator in MATalpha cells. Interestingly, deletion of TRT2 results in an increase in CBT1 mRNA levels in MATa cells, indicating a potential tRNA position effect. The transcription of TRT2 itself is unaffected by the presence of the alpha2 operator, suggesting a hierarchy that favors assembly of the RNA polymerase III complex versus assembly of adjacent alpha2 operator-mediated repressed chromatin structures. This proposed hierarchy could explain how tRNA genes function as barriers to the propagation of repressive chromatin.
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MESH Headings
- ATP-Binding Cassette Transporters
- Chromosomes, Fungal
- Fungal Proteins/genetics
- Gene Deletion
- Gene Expression Regulation, Fungal
- Gene Silencing
- Genes, Fungal
- Glycoproteins
- Histones/metabolism
- Homeodomain Proteins/genetics
- Operator Regions, Genetic
- RNA, Messenger/biosynthesis
- RNA, Transfer, Thr/biosynthesis
- RNA, Transfer, Thr/genetics
- Repressor Proteins/genetics
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae/metabolism
- Saccharomyces cerevisiae Proteins/biosynthesis
- Saccharomyces cerevisiae Proteins/genetics
- Transcription, Genetic
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Affiliation(s)
- Tiffany A Simms
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA
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Sharma VM, Li B, Reese JC. SWI/SNF-dependent chromatin remodeling of RNR3 requires TAF(II)s and the general transcription machinery. Genes Dev 2003; 17:502-15. [PMID: 12600943 PMCID: PMC195993 DOI: 10.1101/gad.1039503] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Gene expression requires the recruitment of chromatin remodeling activities and general transcription factors (GTFs) to promoters. Whereas the role of activators in recruiting chromatin remodeling activities has been clearly demonstrated, the contributions of the transcription machinery have not been firmly established. Here we demonstrate that the remodeling of the RNR3 promoter requires a number of GTFs, mediator and RNA polymerase II. We also show that remodeling is dependent upon the SWI/SNF complex, and that TFIID and RNA polymerase II are required for its recruitment to the promoter. In contrast, Gcn5p-dependent histone acetylation occurs independently of TFIID and RNA polymerase II function, and we provide evidence that acetylation increases the extent of nucleosome remodeling, but is not required for SWI/SNF recruitment. Thus, the general transcription machinery can contribute to nucleosome remodeling by mediating the association of SWI/SNF with promoters, thereby revealing a novel pathway for the recruitment of chromatin remodeling activities.
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Affiliation(s)
- Vishva Mitra Sharma
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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10
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Gavin IM, Kladde MP, Simpson RT. Tup1p represses Mcm1p transcriptional activation and chromatin remodeling of an a-cell-specific gene. EMBO J 2000; 19:5875-83. [PMID: 11060038 PMCID: PMC305800 DOI: 10.1093/emboj/19.21.5875] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2000] [Revised: 09/08/2000] [Accepted: 09/12/2000] [Indexed: 11/13/2022] Open
Abstract
In yeast, a number of regulatory proteins expressed only in specific cell types interact with general transcription factors in a combinatorial manner to control expression of cell-type-specific genes. We report a detailed analysis of activation and repression events that occur at the promoter of the a-cell-specific STE6 gene fused to a beta-galactosidase gene in a yeast minichromosome, as well as factors that control the chromatin structure of this promoter both in the minichromosome and in the genomic STE6 locus. Mcm1p results in chromatin remodeling and is responsible for all transcriptional activity from the STE6 promoter in both wild-type a and alpha cells. Matalpha2p cooperates with Tup1p to block both chromatin remodeling and Mcm1p-associated activation. While Matalpha2p represses only Mcm1p, the Tup1p-mediated repression involves both Mcm1p-dependent and -independent mechanisms. Swi/Snf and Gcn5p, required for full induction of the STE6 gene, do not contribute to chromatin remodeling. We suggest that Tup1p can contribute to repression by blocking transcriptional activators, in addition to interacting with transcription machinery and stabilizing chromatin.
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Affiliation(s)
- I M Gavin
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, 308 Althouse Laboratory, University Park, PA 16802, USA
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11
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Shimizu M, Mori T, Sakurai T, Shindo H. Destabilization of nucleosomes by an unusual DNA conformation adopted by poly(dA) small middle dotpoly(dT) tracts in vivo. EMBO J 2000; 19:3358-65. [PMID: 10880448 PMCID: PMC313933 DOI: 10.1093/emboj/19.13.3358] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Poly(dA) small middle dotpoly(dT) tracts are common and often found upstream of genes in eukaryotes. It has been suggested that poly(dA) small middle dotpoly(dT) promotes transcription in vivo by affecting nucleosome formation. On the other hand, in vitro studies show that poly(dA) small middle dotpoly(dT) can be easily incorporated into nucleosomes. Therefore, the roles of these tracts in nucleosome organization in vivo remain to be established. We have developed an assay system that can evaluate nucleosome formation in yeast cells, and demonstrated that relatively longer tracts such as A(15)TATA(16) and A(34) disrupt an array of positioned nucleosomes, whereas a shorter A(5)TATA(4) tract is incorporated in positioned nucleosomes of yeast minichromosomes. Thus, nucleosomes are destabilized by poly(dA) small middle dotpoly(dT) in vivo in a length-dependent manner. Furthermore, in vivo UV footprinting revealed that the longer tracts adopt an unusual DNA structure in yeast cells that corresponds to the B' conformation described in vitro. Our results support a mechanism in which a unique poly(dA) small middle dot poly(dT) conformation presets chromatin structure to which transcription factors are accessible.
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Affiliation(s)
- M Shimizu
- Department of Chemistry, Meisei University, Hino, Tokyo 191-8506 and School of Pharmacy, Tokyo University of Pharmacy and Life Science, Hachioji, Tokyo 192-0392, Japan.
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12
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Ducker CE, Simpson RT. The organized chromatin domain of the repressed yeast a cell-specific gene STE6 contains two molecules of the corepressor Tup1p per nucleosome. EMBO J 2000; 19:400-9. [PMID: 10654939 PMCID: PMC305577 DOI: 10.1093/emboj/19.3.400] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In yeast alpha cells the a cell-specific genes STE6 and BAR1 are packaged as gene-sized chromatin domains of positioned nucleosomes. Organized chromatin depends on Tup1p, a corepressor that interacts with the N-terminal regions of H3 and H4. If Tup1p functions to organize or stabilize a chromatin domain, the protein might be expected to be present at a level stoichiometric with nucleosomes. Chromatin immunoprecipitation assays using Tup1p antibodies showed Tup1p to be associated with the entire genomic STE6 coding region. To determine stoichiometry of Tup1p associated with the gene, a yeast plasmid containing varying lengths of the STE6 gene including flanking control regions and an Escherichia coli lac operator sequence was constructed. After assembly into chromatin in vivo in Saccharomyces cerevisiae, minichromosomes were isolated using an immobilized lac repressor. In these experiments, Tup1p was found to be specifically associated with repressed STE6 chromatin in vivo at a ratio of about two molecules of the corepressor per nucleosome. These observations strongly suggest a structural role for Tup1p in repression and constrain models for organized chromatin in repressive domains.
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Affiliation(s)
- C E Ducker
- Department of Biochemistry and Molecular Biology, 308 Althouse, Pennsylvania State University, University Park, PA 16802, USA
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13
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Ravindra A, Weiss K, Simpson RT. High-resolution structural analysis of chromatin at specific loci: Saccharomyces cerevisiae silent mating-type locus HMRa. Mol Cell Biol 1999; 19:7944-50. [PMID: 10567520 PMCID: PMC84879 DOI: 10.1128/mcb.19.12.7944] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Genetic and biochemical evidence implicates chromatin structure in the silencing of the two quiescent mating-type loci near the telomeres of chromosome III in yeast. With high-resolution micrococcal nuclease mapping, we show that the HMRa locus has 12 precisely positioned nucleosomes spanning the distance between the E and I silencer elements. The nucleosomes are arranged in pairs with very short linkers; the pairs are separated from one another by longer linkers of approximately 20 bp. Both the basic amino-terminal region of histone H4 and the silent information regulator protein Sir3p are necessary for the organized repressive chromatin structure of the silent locus. Compared to HMRa, only small differences in the availability of the TATA box are present for the promoter in the cassette at the active MATa locus. Features of the chromatin structure of this silent locus compared to the previously studied HMLalpha locus suggest differences in the mechanisms of silencing and may relate to donor selection during mating-type interconversion.
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Affiliation(s)
- A Ravindra
- Department of Biochemistry and Molecular Biology, The Center for Gene Regulation, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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14
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Weiss K, Simpson RT. High-resolution structural analysis of chromatin at specific loci: Saccharomyces cerevisiae silent mating type locus HMLalpha. Mol Cell Biol 1998; 18:5392-403. [PMID: 9710623 PMCID: PMC109124 DOI: 10.1128/mcb.18.9.5392] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/1998] [Accepted: 06/04/1998] [Indexed: 11/20/2022] Open
Abstract
Genetic studies have suggested that chromatin structure is involved in repression of the silent mating type loci in Saccharomyces cerevisiae. Chromatin mapping at nucleotide resolution of the transcriptionally silent HMLalpha and the active MATalpha shows that unique organized chromatin structure characterizes the silent state of HMLalpha. Precisely positioned nucleosomes abutting the silencers extend over the alpha1 and alpha2 coding regions. The HO endonuclease recognition site, nuclease hypersensitive at MATalpha, is protected at HMLalpha. Although two precisely positioned nucleosomes incorporate transcription start sites at HMLalpha, the promoter region of the alpha1 and alpha2 genes is nucleosome free and more nuclease sensitive in the repressed than in the transcribed locus. Mutations in genes essential for HML silencing disrupt the nucleosome array near HML-I but not in the vicinity of HML-E, which is closer to the telomere of chromosome III. At the promoter and the HO site, the structure of HMLalpha in Sir protein and histone H4 N-terminal deletion mutants is identical to that of the transcriptionally active MATalpha. The discontinuous chromatin structure of HMLalpha contrasts with the continuous array of nucleosomes found at repressed a-cell-specific genes and the recombination enhancer. Punctuation at HMLalpha may be necessary for higher-order structure or karyoskeleton interactions. The unique chromatin architecture of HMLalpha may relate to the combined requirements of transcriptional repression and recombinational competence.
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Affiliation(s)
- K Weiss
- Department of Biochemistry and Molecular Biology, The Center for Gene Regulation, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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15
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Xu M, Simpson RT, Kladde MP. Gal4p-mediated chromatin remodeling depends on binding site position in nucleosomes but does not require DNA replication. Mol Cell Biol 1998; 18:1201-12. [PMID: 9488435 PMCID: PMC108833 DOI: 10.1128/mcb.18.3.1201] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Biochemical studies have demonstrated decreased binding of various proteins to DNA in nucleosome cores as their cognate sites are moved from the edge of the nucleosome to the pseudodyad (center). However, to date no study has addressed whether this structural characteristic of nucleosomes modulates the function of a transcription factor in living cells, where processes of DNA replication and chromatin modification or remodeling could significantly affect factor binding. Using a sensitive, high-resolution methyltransferase assay, we have monitored the ability of Gal4p in vivo to interact with a nucleosome at positions that are known to be inaccessible in nucleosome cores in vitro. Gal4p efficiently bound a single cognate site (UASG) centered at 41 bp from the edge of a positioned nucleosome, perturbing chromatin structure and inducing transcription. DNA binding and chromatin perturbation accompanying this interaction also occurred in the presence of hydroxyurea, indicating that DNA replication is not necessary for Gal4p-mediated nucleosome disruption. These data extend previous studies, which demonstrated DNA replication-independent chromatin remodeling, by showing that a single dimer of Gal4p, without the benefit of cooperative interactions that occur at complex wild-type promoters, is competent for invasion of a preestablished nucleosome. When the UASG was localized at the nucleosomal pseudodyad, relative occupancy by Gal4p, nucleosome disruption, and transcriptional activation were substantially compromised. Therefore, despite the increased nucleosome binding capability of Gal4p in cells, the precise translational position of a factor binding site in one nucleosome in an array can affect the ability of a transcriptional regulator to overcome the repressive influence of chromatin.
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Affiliation(s)
- M Xu
- Department of Biochemistry and Molecular Biology and Center for Gene Regulation, The Pennsylvania State University, University Park 16802-4500, USA
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16
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Wechser MA, Kladde MP, Alfieri JA, Peterson CL. Effects of Sin- versions of histone H4 on yeast chromatin structure and function. EMBO J 1997; 16:2086-95. [PMID: 9155034 PMCID: PMC1169811 DOI: 10.1093/emboj/16.8.2086] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Previous studies have identified single amino acid changes within either histone H3 or H4 (Sin- versions) that allow transcription in the absence of the yeast SWI-SNF complex. The histone H4 mutants are competent for nucleosome assembly in vivo, and the residues that are altered appear to define a discrete domain on the surface of the histone octamer. We have analyzed the effects of the Sin- versions of histone H4 on transcription and chromatin structure in vivo. These histone H4 mutants cause an increased accessibility of nucleosomal DNA to Dam methyltransferase and to micrococcal nuclease. Sin- derivatives of histone H4 also grossly impair the ability of nucleosomes to constrain supercoils in vivo. Nucleosome-mediated repression of the PHO5 gene is severely impaired by these histone H4 mutants; PHO5 expression is derepressed to 31% of the wild-type induced level. In contrast to the induction caused by nucleosome depletion, full PHO5 derepression by Sin- versions of histone H4 requires upstream regulatory elements. In addition, Sin- derivatives of histone H4 do not activate expression from CYC1 or GAL1 promoters that lack UAS elements. We propose that these Sin- mutations alter histone-DNA contact residues that play key roles in restricting the accessibility of nucleosomal DNA to transcription factors.
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Affiliation(s)
- M A Wechser
- Program in Molecular Medicine and Department of Biochemistry and Molecular Biology, University of Massachusetts Medical Center, Worcester 01605, USA
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17
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Redd MJ, Stark MR, Johnson AD. Accessibility of alpha 2-repressed promoters to the activator Gal4. Mol Cell Biol 1996; 16:2865-9. [PMID: 8649396 PMCID: PMC231279 DOI: 10.1128/mcb.16.6.2865] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
It has been proposed that eukaryotic repressors of transcription can act by organizing chromatin, thereby preventing the accessibility of nearby DNA to activator proteins required for transcription initiation. In this study, we test this idea for the yeast alpha 2 repressor using a simple, artificial promoter that contains a single binding site for the activator protein Gal4 and a single binding site for the repressor alpha 2. When both the repressor and the activator are expressed in the same cell, the artificial promoter is efficiently repressed. In vivo footprinting experiments demonstrate that Gal4 can occupy its binding site even when the promoter is repressed. This result indicates that alpha 2-directed repression must result from interference with some stage in transcription initiation other than activator binding to DNA.
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Affiliation(s)
- M J Redd
- Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0414, USA
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Godde JS, Nakatani Y, Wolffe AP. The amino-terminal tails of the core histones and the translational position of the TATA box determine TBP/TFIIA association with nucleosomal DNA. Nucleic Acids Res 1995; 23:4557-64. [PMID: 8524642 PMCID: PMC307425 DOI: 10.1093/nar/23.22.4557] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
We establish that the TATA binding protein (TBP) in the presence of TFIIA recognizes the TATA box in nucleosomal DNA dependent on the dissociation of the amino-terminal tails of the core histones from the nucleosome and the position of the TATA box within the nucleosome. We examine TBP/TFIIA access to the TATA box with this sequence placed in four distinct rotational frames with reference to the histone surface and at three distinct translational positions at the edge, side and dyad axis of the nucleosome. Under our experimental conditions, we find that the preferential translational position at which TBP/TFIIA can bind the TATA box is within linker DNA at the edge of the nucleosome and that binding is facilitated if contacts made by the amino-terminal tails of the histones with nucleosomal DNA are eliminated. TBP/TFIIA binding to DNA at the edge of the nucleosome occurs with the TATA box in all four rotational positions. This is indicative of TBP/TFIIA association directing the dissociation of the TATA box from the surface of the histone octamer.
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Affiliation(s)
- J S Godde
- Laboratory of Molecular Embryology, National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892-2710, USA
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19
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Patterton HG, Simpson RT. Modified curved DNA that could allow local DNA underwinding at the nucleosomal pseudodyad fails to position a nucleosome in vivo. Nucleic Acids Res 1995; 23:4170-9. [PMID: 7479081 PMCID: PMC307359 DOI: 10.1093/nar/23.20.4170] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
In competitive in vitro reconstitution experiments synthetic DNA composed of tandem repeats of the repetitive sequence (A/T)3NN(G/C)3NN, specifically the 20 bp 'TG sequence' (5'-TCGGTGTTAGAGCCTGTAAC-3'), was reported to associate with the histone octamer with an affinity higher than that of nucleosomally derived DNA. However, at least two groups have independently shown that tandem repeats of the TG sequence do not accommodate a stably positioned nucleosome in vivo. It was suggested that the anisotropic flexibility of the TG sequence, governed by a 10 bp sequence periodicity, is incompatible with the required underwinding of the DNA helix at the nucleosome pseudodyad while maintaining a bending preference that can be accommodated in the remainder of the nucleosome. Here we test this hypothesis directly by studying the in vivo nucleosomal structure of modified TG sequences designed to accommodate underwinding at the pseudodyad. We show that these modifications are not sufficient to allow stable incorporation of the TG sequence repeat into a nucleosome in vivo, but do note invasion from one end of the TG heptamer of a translationally random but rotationally constrained nucleosome. We discuss possible reasons for the absence of nucleosomes from the TG sequence in vivo.
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Affiliation(s)
- H G Patterton
- LCDB/NIDDK, National Institutes of Health, Bethesda, MD 20892-2715, USA
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20
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Smith DL, Desai AB, Johnson AD. DNA bending by the a1 and alpha 2 homeodomain proteins from yeast. Nucleic Acids Res 1995; 23:1239-43. [PMID: 7739902 PMCID: PMC306837 DOI: 10.1093/nar/23.7.1239] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Structural and biochemical studies of monomer homeodomain-DNA complexes have not so far revealed any cases of pronounced DNA distortion. In this paper we show that multimeric complexes of the yeast homeodomain proteins a1 and alpha 2 induced significant bends in their operators upon binding. Based on a series of circular permutation experiments, we found that a dimer of alpha 2 bound to operator DNA produced a mild bend in the DNA, whereas the alpha 2-MCM1-DNA and the a1-alpha 2-DNA complexes exhibited much sharper bends. As these latter two complexes represent the in vivo form of DNA-bound a1 and alpha 2, we conclude that, in the cell, these homeodomain proteins are associated with pronounced bends in DNA. We discuss possible roles for these bends in transcriptional repression.
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Affiliation(s)
- D L Smith
- Department of Microbiology and Immunology, University of California, San Francisco 94143, USA
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21
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Gerlach VL, Whitehall SK, Geiduschek EP, Brow DA. TFIIIB placement on a yeast U6 RNA gene in vivo is directed primarily by TFIIIC rather than by sequence-specific DNA contacts. Mol Cell Biol 1995; 15:1455-66. [PMID: 7862139 PMCID: PMC230370 DOI: 10.1128/mcb.15.3.1455] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The Saccharomyces cerevisiae U6 RNA gene (SNR6), which is transcribed by RNA polymerase III, has an unusual combination of promoter elements: an upstream TATA box, an intragenic A block, and a downstream B block. In tRNA genes, the A and B blocks are binding sites for the transcription initiation factor TFIIIC, which positions TFIIIB a fixed distance upstream of the A block. However, in vitro transcription of SNR6 with purified components requires neither TFIIIC nor the A and B blocks, presumably because TFIIIB recognizes the upstream sequences directly. Here we demonstrate that TFIIIB placement on SNR6 in vivo is directed primarily by the TFIIIC-binding elements rather than by upstream sequences. We show that the A block is a stronger start site determinant than the upstream sequences when the two are uncoupled by an insertion mutation. Furthermore, while TFIIIC-independent in vitro transcription of SNR6 is highly sensitive to TATA box point mutations, in vivo initiation on SNR6 is only marginally sensitive to such mutations unless the A block is mutated. Intriguingly, a deletion downstream of the U6 RNA coding region that reduces A-to-B block spacing also increases in vivo dependence on the TATA box. Moreover, this deletion results in the appearance of micrococcal nuclease-hypersensitive sites in the TFIIIB chromatin footprint, indicating that TFIIIB binding is disrupted by a mutation 150 bp distant. This and additional chromatin footprinting data suggest that SNR6 is assembled into a nucleoprotein complex that facilitates the TFIIIC-dependent binding of TFIIIB.
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MESH Headings
- Base Sequence
- Binding Sites
- DNA Primers
- DNA, Fungal/genetics
- DNA, Fungal/metabolism
- Genes, Fungal
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Oligodeoxyribonucleotides
- Plasmids
- Polymerase Chain Reaction
- RNA, Fungal/biosynthesis
- RNA, Fungal/genetics
- RNA, Small Nuclear/genetics
- Regulatory Sequences, Nucleic Acid
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae/metabolism
- Sequence Deletion
- Structure-Activity Relationship
- TATA Box
- Transcription Factor TFIIB
- Transcription Factors/isolation & purification
- Transcription Factors/metabolism
- Transcription Factors, TFIII
- Transcription, Genetic
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Affiliation(s)
- V L Gerlach
- Department of Biomolecular Chemistry, University of Wisconsin Medical School, Madison 53706-1532
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