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Ouasti F, Audin M, Fréon K, Quivy JP, Tachekort M, Cesard E, Thureau A, Ropars V, Fernández Varela P, Moal G, Soumana-Amadou I, Uryga A, Legrand P, Andreani J, Guerois R, Almouzni G, Lambert S, Ochsenbein F. Disordered regions and folded modules in CAF-1 promote histone deposition in Schizosaccharomyces pombe. eLife 2024; 12:RP91461. [PMID: 38376141 PMCID: PMC10942606 DOI: 10.7554/elife.91461] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/21/2024] Open
Abstract
Genome and epigenome integrity in eukaryotes depends on the proper coupling of histone deposition with DNA synthesis. This process relies on the evolutionary conserved histone chaperone CAF-1 for which the links between structure and functions are still a puzzle. While studies of the Saccharomyces cerevisiae CAF-1 complex enabled to propose a model for the histone deposition mechanism, we still lack a framework to demonstrate its generality and in particular, how its interaction with the polymerase accessory factor PCNA is operating. Here, we reconstituted a complete SpCAF-1 from fission yeast. We characterized its dynamic structure using NMR, SAXS and molecular modeling together with in vitro and in vivo functional studies on rationally designed interaction mutants. Importantly, we identify the unfolded nature of the acidic domain which folds up when binding to histones. We also show how the long KER helix mediates DNA binding and stimulates SpCAF-1 association with PCNA. Our study highlights how the organization of CAF-1 comprising both disordered regions and folded modules enables the dynamics of multiple interactions to promote synthesis-coupled histone deposition essential for its DNA replication, heterochromatin maintenance, and genome stability functions.
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Affiliation(s)
- Fouad Ouasti
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Institute JoliotGif-sur-YvetteFrance
| | - Maxime Audin
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Institute JoliotGif-sur-YvetteFrance
| | - Karine Fréon
- Institut Curie, PSL Research University, CNRS UMR 3348, INSERM U1278, Université Paris-Saclay, Equipe labellisée Ligue contre le CancerOrsayFrance
| | - Jean-Pierre Quivy
- Institut Curie, PSL Research University, CNRS, Sorbonne Université,CNRS UMR3664, Nuclear Dynamics Unit, Équipe Labellisée Ligue contre le CancerParisFrance
| | - Mehdi Tachekort
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Institute JoliotGif-sur-YvetteFrance
| | - Elizabeth Cesard
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Institute JoliotGif-sur-YvetteFrance
| | - Aurélien Thureau
- Synchrotron SOLEIL, HelioBio group, l'Orme des MerisiersSaint-AubinFrance
| | - Virginie Ropars
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Institute JoliotGif-sur-YvetteFrance
| | - Paloma Fernández Varela
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Institute JoliotGif-sur-YvetteFrance
| | - Gwenaelle Moal
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Institute JoliotGif-sur-YvetteFrance
| | - Ibrahim Soumana-Amadou
- Institut Curie, PSL Research University, CNRS UMR 3348, INSERM U1278, Université Paris-Saclay, Equipe labellisée Ligue contre le CancerOrsayFrance
| | - Aleksandra Uryga
- Institut Curie, PSL Research University, CNRS UMR 3348, INSERM U1278, Université Paris-Saclay, Equipe labellisée Ligue contre le CancerOrsayFrance
| | - Pierre Legrand
- Synchrotron SOLEIL, HelioBio group, l'Orme des MerisiersSaint-AubinFrance
| | - Jessica Andreani
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Institute JoliotGif-sur-YvetteFrance
| | - Raphaël Guerois
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Institute JoliotGif-sur-YvetteFrance
| | - Geneviève Almouzni
- Institut Curie, PSL Research University, CNRS, Sorbonne Université,CNRS UMR3664, Nuclear Dynamics Unit, Équipe Labellisée Ligue contre le CancerParisFrance
| | - Sarah Lambert
- Institut Curie, PSL Research University, CNRS UMR 3348, INSERM U1278, Université Paris-Saclay, Equipe labellisée Ligue contre le CancerOrsayFrance
| | - Francoise Ochsenbein
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Institute JoliotGif-sur-YvetteFrance
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2
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Singha R, Aggarwal R, Sanyal K. Negative regulation of biofilm development by the CUG-Ser1 clade-specific histone H3 variant is dependent on the canonical histone chaperone CAF-1 complex in Candida albicans. Mol Microbiol 2023; 119:574-585. [PMID: 36855815 DOI: 10.1111/mmi.15050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2022] [Revised: 02/21/2023] [Accepted: 02/26/2023] [Indexed: 03/02/2023]
Abstract
The CUG-Ser1 clade-specific histone H3 variant (H3VCTG ) has been reported to be a negative regulator of planktonic to biofilm growth transition in Candida albicans. The preferential binding of H3VCTG at the biofilm gene promoters makes chromatin repressive for the biofilm mode of growth. The two evolutionarily conserved chaperone complexes involved in incorporating histone H3 are CAF-1 and HIRA. In this study, we sought to identify the chaperone complex(es) involved in loading H3VCTG . We demonstrate that C. albicans cells lacking either Cac1 or Cac2 subunit of the CAF-1 chaperone complex, exhibit a hyper-filamentation phenotype on solid surfaces and form more robust biofilms than wild-type cells, thereby mimicking the phenotype of the H3VCTG null mutant. None of the subunits of the HIRA chaperone complex shows any significant difference in biofilm growth as compared to the wild type. The occupancy of H3VCTG is found to be significantly reduced at the promoters of biofilm genes in the absence of CAF-1 subunits. Hence, we provide evidence that CAF-1, a chaperone known to load canonical histone H3 in mammalian cells, is involved in chaperoning of variant histone H3VCTG at the biofilm gene promoters in C. albicans. Our findings also illustrate the acquisition of an unconventional role of the CAF-1 chaperone complex in morphogenesis in C. albicans.
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Affiliation(s)
- Rima Singha
- Molecular Mycology Laboratory, Molecular Biology and Genetics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India
| | - Rashi Aggarwal
- Molecular Mycology Laboratory, Molecular Biology and Genetics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India
| | - Kaustuv Sanyal
- Molecular Mycology Laboratory, Molecular Biology and Genetics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India
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3
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Kudo H, Arakawa GY, Shirai S, Ogawa M, Shindo H, Hosaka M, Tokuoka M. New role of a histone chaperone, HirA: Involvement in kojic acid production associated with culture conditions in Aspergillusoryzae. J Biosci Bioeng 2021; 133:235-242. [PMID: 34952787 DOI: 10.1016/j.jbiosc.2021.12.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2021] [Revised: 10/29/2021] [Accepted: 12/05/2021] [Indexed: 10/19/2022]
Abstract
Kojic acid (KA) is a representative secondary metabolite of Aspergillus oryzae, but the underlying molecular mechanisms that regulate KA production are unknown. This study tried to find a genetic factor of KA production in A. oryzae, with a special focus on liquid cultures. We screened a gene predicted to encode HirA, a subunit of the histone chaperon, the HIR complex. A gene disruption strain of hirA showed decreased KA production in liquid culture, whereas it showed increased KA production in plate culture. We confirmed that a decrease/increase of KA production observed by hirA disruption was caused by altered expression of kojA and kojR. These observations suggested the regulatory role of histone chaperon in secondary metabolism in filamentous fungi. So far as we know, this report is the first showing that disruption of a gene resulted in the opposite effect on KA production in liquid and plate cultures in A. oryzae.
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Affiliation(s)
- Hayato Kudo
- Graduate School of Agriculture, Department of Fermentation Science and Technology, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan
| | - Gen-Ya Arakawa
- Graduate School of Agriculture, Department of Fermentation Science and Technology, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan
| | - Saya Shirai
- Graduate School of Agriculture, Department of Fermentation Science and Technology, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan
| | - Masahiro Ogawa
- Noda Institute for Scientific Research, 338 Noda, Noda, Chiba 278-0037, Japan
| | - Hitoshi Shindo
- Graduate School of Agriculture, Department of Fermentation Science and Technology, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan; Department of Fermentation Science, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan
| | - Masaru Hosaka
- Graduate School of Agriculture, Department of Fermentation Science and Technology, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan; Department of Fermentation Science, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan
| | - Masafumi Tokuoka
- Graduate School of Agriculture, Department of Fermentation Science and Technology, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan; Department of Fermentation Science, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan.
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4
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Wu PS, Grosser J, Cameron DP, Baranello L, Ström L. Deficiency of Polη in Saccharomyces cerevisiae reveals the impact of transcription on damage-induced cohesion. PLoS Genet 2021; 17:e1009763. [PMID: 34499654 PMCID: PMC8454932 DOI: 10.1371/journal.pgen.1009763] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Revised: 09/21/2021] [Accepted: 08/05/2021] [Indexed: 11/18/2022] Open
Abstract
The structural maintenance of chromosome (SMC) complex cohesin mediates sister chromatid cohesion established during replication, and damage-induced cohesion formed in response to DSBs post-replication. The translesion synthesis polymerase Polη is required for damage-induced cohesion through a hitherto unknown mechanism. Since Polη is functionally associated with transcription, and transcription triggers de novo cohesion in Schizosaccharomyces pombe, we hypothesized that transcription facilitates damage-induced cohesion in Saccharomyces cerevisiae. Here, we show dysregulated transcriptional profiles in the Polη null mutant (rad30Δ), where genes involved in chromatin assembly and positive transcription regulation were downregulated. In addition, chromatin association of RNA polymerase II was reduced at promoters and coding regions in rad30Δ compared to WT cells, while occupancy of the H2A.Z variant (Htz1) at promoters was increased in rad30Δ cells. Perturbing histone exchange at promoters inactivated damage-induced cohesion, similarly to deletion of the RAD30 gene. Conversely, altering regulation of transcription elongation suppressed the deficient damage-induced cohesion in rad30Δ cells. Furthermore, transcription inhibition negatively affected formation of damage-induced cohesion. These results indicate that the transcriptional deregulation of the Polη null mutant is connected with its reduced capacity to establish damage-induced cohesion. This also suggests a linkage between regulation of transcription and formation of damage-induced cohesion after replication.
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Affiliation(s)
- Pei-Shang Wu
- Karolinska Institutet, Department of Cell and Molecular Biology, Stockholm, Sweden
| | - Jan Grosser
- Karolinska Institutet, Department of Cell and Molecular Biology, Stockholm, Sweden
| | - Donald P. Cameron
- Karolinska Institutet, Department of Cell and Molecular Biology, Stockholm, Sweden
| | - Laura Baranello
- Karolinska Institutet, Department of Cell and Molecular Biology, Stockholm, Sweden
| | - Lena Ström
- Karolinska Institutet, Department of Cell and Molecular Biology, Stockholm, Sweden
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5
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Insights into the roles of histone chaperones in nucleosome assembly and disassembly in virus infection. Virus Res 2021; 297:198395. [PMID: 33737155 DOI: 10.1016/j.virusres.2021.198395] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2020] [Revised: 03/10/2021] [Accepted: 03/11/2021] [Indexed: 11/23/2022]
Abstract
Nucleosomes are assembled or disassembled with the aid of histone chaperones in a cell. Viruses can exist either as minichromosomes/episomes or can integrate into the host genome and in both the cases the viral proteins interact and manipulate the cellular nucleosome assembly machinery to ensure their survival and propagation. Recent studies have provided insight into the mechanism and role of histone chaperones in nucleosome assembly and disassembly on the virus genome. Further, the interactions between viral proteins and histone chaperones have been implicated in the integration of the virus genome into the host genome. This review highlights the recent progress and future challenges in understanding the role of histone chaperones in viruses with DNA or RNA genome and their role in governing viral pathogenesis.
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6
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Goffová I, Fajkus J. The rDNA Loci-Intersections of Replication, Transcription, and Repair Pathways. Int J Mol Sci 2021; 22:1302. [PMID: 33525595 PMCID: PMC7865372 DOI: 10.3390/ijms22031302] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 01/25/2021] [Accepted: 01/25/2021] [Indexed: 12/28/2022] Open
Abstract
Genes encoding ribosomal RNA (rDNA) are essential for cell survival and are particularly sensitive to factors leading to genomic instability. Their repetitive character makes them prone to inappropriate recombinational events arising from collision of transcriptional and replication machineries, resulting in unstable rDNA copy numbers. In this review, we summarize current knowledge on the structure and organization of rDNA, its role in sensing changes in the genome, and its linkage to aging. We also review recent findings on the main factors involved in chromatin assembly and DNA repair in the maintenance of rDNA stability in the model plants Arabidopsis thaliana and the moss Physcomitrella patens, providing a view across the plant evolutionary tree.
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Affiliation(s)
- Ivana Goffová
- Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, CZ-61137 Brno, Czech Republic;
- Chromatin Molecular Complexes, Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Masaryk University, CZ-62500 Brno, Czech Republic
| | - Jiří Fajkus
- Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, CZ-61137 Brno, Czech Republic;
- Chromatin Molecular Complexes, Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Masaryk University, CZ-62500 Brno, Czech Republic
- Department of Cell Biology and Radiobiology, Institute of Biophysics of the Czech Academy of Sciences, CZ-61265 Brno, Czech Republic
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7
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Young TJ, Cui Y, Pfeffer C, Hobbs E, Liu W, Irudayaraj J, Kirchmaier AL. CAF-1 and Rtt101p function within the replication-coupled chromatin assembly network to promote H4 K16ac, preventing ectopic silencing. PLoS Genet 2020; 16:e1009226. [PMID: 33284793 PMCID: PMC7746308 DOI: 10.1371/journal.pgen.1009226] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Revised: 12/17/2020] [Accepted: 10/26/2020] [Indexed: 11/18/2022] Open
Abstract
Replication-coupled chromatin assembly is achieved by a network of alternate pathways containing different chromatin assembly factors and histone-modifying enzymes that coordinate deposition of nucleosomes at the replication fork. Here we describe the organization of a CAF-1-dependent pathway in Saccharomyces cerevisiae that regulates acetylation of histone H4 K16. We demonstrate factors that function in this CAF-1-dependent pathway are important for preventing establishment of silenced states at inappropriate genomic sites using a crippled HMR locus as a model, while factors specific to other assembly pathways do not. This CAF-1-dependent pathway required the cullin Rtt101p, but was functionally distinct from an alternate pathway involving Rtt101p-dependent ubiquitination of histone H3 and the chromatin assembly factor Rtt106p. A major implication from this work is that cells have the inherent ability to create different chromatin modification patterns during DNA replication via differential processing and deposition of histones by distinct chromatin assembly pathways within the network.
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Affiliation(s)
- Tiffany J. Young
- Department of Biochemistry, Purdue University, West Lafayette, Indiana, United States of America
- Purdue University Center for Cancer Research, West Lafayette, Indiana, United States of America
- Bindley Bioscience Center, Purdue University, West Lafayette, Indiana, United States of America
| | - Yi Cui
- Purdue University Center for Cancer Research, West Lafayette, Indiana, United States of America
- Bindley Bioscience Center, Purdue University, West Lafayette, Indiana, United States of America
- Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, Indiana, United States of America
| | - Claire Pfeffer
- Department of Biochemistry, Purdue University, West Lafayette, Indiana, United States of America
| | - Emilie Hobbs
- Department of Biochemistry, Purdue University, West Lafayette, Indiana, United States of America
| | - Wenjie Liu
- Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, Indiana, United States of America
- Department of Bioengineering, Cancer Center at Illinois, Micro and Nanotechnology Laboratory, University of Illinois at Urbana Champaign, Urbana, Illinois, United States of America
| | - Joseph Irudayaraj
- Purdue University Center for Cancer Research, West Lafayette, Indiana, United States of America
- Bindley Bioscience Center, Purdue University, West Lafayette, Indiana, United States of America
- Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, Indiana, United States of America
- Department of Bioengineering, Cancer Center at Illinois, Micro and Nanotechnology Laboratory, University of Illinois at Urbana Champaign, Urbana, Illinois, United States of America
| | - Ann L. Kirchmaier
- Department of Biochemistry, Purdue University, West Lafayette, Indiana, United States of America
- Purdue University Center for Cancer Research, West Lafayette, Indiana, United States of America
- Bindley Bioscience Center, Purdue University, West Lafayette, Indiana, United States of America
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8
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Synergy of Hir1, Ssn6, and Snf2 global regulators is the functional determinant of a Mac1 transcriptional switch in S. cerevisiae copper homeostasis. Curr Genet 2019; 65:799-816. [DOI: 10.1007/s00294-019-00935-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2018] [Revised: 12/21/2018] [Accepted: 01/11/2019] [Indexed: 12/15/2022]
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9
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Sauer PV, Gu Y, Liu WH, Mattiroli F, Panne D, Luger K, Churchill MEA. Mechanistic insights into histone deposition and nucleosome assembly by the chromatin assembly factor-1. Nucleic Acids Res 2018; 46:9907-9917. [PMID: 30239791 PMCID: PMC6212844 DOI: 10.1093/nar/gky823] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 09/15/2018] [Indexed: 02/03/2023] Open
Abstract
Eukaryotic chromatin is a highly dynamic structure with essential roles in virtually all DNA-dependent cellular processes. Nucleosomes are a barrier to DNA access, and during DNA replication, they are disassembled ahead of the replication machinery (the replisome) and reassembled following its passage. The Histone chaperone Chromatin Assembly Factor-1 (CAF-1) interacts with the replisome and deposits H3-H4 directly onto newly synthesized DNA. Therefore, CAF-1 is important for the establishment and propagation of chromatin structure. The molecular mechanism by which CAF-1 mediates H3-H4 deposition has remained unclear. However, recent studies have revealed new insights into the architecture and stoichiometry of the trimeric CAF-1 complex and how it interacts with and deposits H3-H4 onto substrate DNA. The CAF-1 trimer binds to a single H3-H4 dimer, which induces a conformational rearrangement in CAF-1 promoting its interaction with substrate DNA. Two CAF-1•H3-H4 complexes co-associate on nucleosome-free DNA depositing (H3-H4)2 tetramers in the first step of nucleosome assembly. Here, we review the progress made in our understanding of CAF-1 structure, mechanism of action, and how CAF-1 contributes to chromatin dynamics during DNA replication.
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Affiliation(s)
- Paul V Sauer
- European Molecular Biology Laboratory, 38042 Grenoble, France
| | - Yajie Gu
- Department of Biochemistry, University of Colorado at Boulder, Boulder, CO 80309, USA
| | - Wallace H Liu
- Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
| | | | - Daniel Panne
- European Molecular Biology Laboratory, 38042 Grenoble, France,Leicester Institute of Structural and Chemical Biology, Department of Molecular and Cell Biology, University of Leicester, Lancaster Road, Leicester LE1 7RH, UK
| | - Karolin Luger
- Department of Biochemistry, University of Colorado at Boulder, Boulder, CO 80309, USA,Howard Hughes Medical Institute, Chevy Chase, MD 20815-6789, USA
| | - Mair EA Churchill
- Department of Pharmacology and Program in Structural Biology and Biochemistry, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA,To whom correspondence should be addressed. Tel: +1 303 724 3670;
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10
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Shaping Chromatin in the Nucleus: The Bricks and the Architects. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2017; 82:1-14. [PMID: 29208640 DOI: 10.1101/sqb.2017.82.033753] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Chromatin organization in the nucleus provides a vast repertoire of information in addition to that encoded genetically. Understanding how this organization impacts genome stability and influences cell fate and tumorigenesis is an area of rapid progress. Considering the nucleosome, the fundamental unit of chromatin structure, the study of histone variants (the bricks) and their selective loading by histone chaperones (the architects) is particularly informative. Here, we report recent advances in understanding how relationships between histone variants and their chaperones contribute to tumorigenesis using cell lines and Xenopus development as model systems. In addition to their role in histone deposition, we also document interactions between histone chaperones and other chromatin factors that govern higher-order structure and control DNA metabolism. We highlight how a fine-tuned assembly line of bricks (H3.3 and CENP-A) and architects (HIRA, HJURP, and DAXX) is key in adaptation to developmental and pathological changes. An example of this conceptual advance is the exquisite sensitivity displayed by p53-null tumor cells to modulation of HJURP, the histone chaperone for CENP-A (CenH3 variant). We discuss how these findings open avenues for novel therapeutic paradigms in cancer care.
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11
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Muñoz-Viana R, Wildhaber T, Trejo-Arellano MS, Mozgová I, Hennig L. Arabidopsis Chromatin Assembly Factor 1 is required for occupancy and position of a subset of nucleosomes. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2017; 92:363-374. [PMID: 28786541 DOI: 10.1111/tpj.13658] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Revised: 07/21/2017] [Accepted: 08/01/2017] [Indexed: 05/23/2023]
Abstract
Chromatin Assembly Factor 1 (CAF-1) is a major nucleosome assembly complex which functions particularly during DNA replication and repair. Here we studied how the nucleosome landscape changes in a CAF-1 mutant in the model plant Arabidopsis thaliana. Globally, most nucleosomes were not affected by loss of CAF-1, indicating the presence of efficient alternative nucleosome assemblers. Nucleosomes that we found depleted in the CAF-1 mutant were enriched in non-transcribed regions, consistent with the notion that CAF-1-independent nucleosome assembly can compensate for loss of CAF-1 mainly in transcribed regions. Depleted nucleosomes were particularly enriched in proximal promoters, suggesting that CAF-1-independent nucleosome assembly mechanisms are often not efficient upstream of transcription start sites. Genes related to plant defense were particularly prone to lose nucleosomes in their promoters upon CAF-1 depletion. Reduced nucleosome occupancy at promoters of many defense-related genes is associated with a primed gene expression state that may considerably increase plant fitness by facilitating plant defense. Together, our results establish that the nucleosome landscape in Arabidopsis is surprisingly robust even in the absence of the dedicated nucleosome assembly machinery CAF-1 and that CAF-1-independent nucleosome assembly mechanisms are less efficient in particular genome regions.
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Affiliation(s)
- Rafael Muñoz-Viana
- Department of Plant Biology and Linnean Center for Plant Biology, Swedish University of Agricultural Sciences, PO-Box 7080, SE-75007, Uppsala, Sweden
| | - Thomas Wildhaber
- Department of Biology, ETH Zürich, Universitätsstrasse 2, CH-8092, Zürich, Switzerland
| | - Minerva S Trejo-Arellano
- Department of Plant Biology and Linnean Center for Plant Biology, Swedish University of Agricultural Sciences, PO-Box 7080, SE-75007, Uppsala, Sweden
| | - Iva Mozgová
- Department of Plant Biology and Linnean Center for Plant Biology, Swedish University of Agricultural Sciences, PO-Box 7080, SE-75007, Uppsala, Sweden
- Institute of Microbiology, Centre Algatech, Opatovický mlýn, 37981, Třeboň, Czech Republic
| | - Lars Hennig
- Department of Plant Biology and Linnean Center for Plant Biology, Swedish University of Agricultural Sciences, PO-Box 7080, SE-75007, Uppsala, Sweden
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12
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Wu MY, Lin CY, Tseng HY, Hsu FM, Chen PY, Kao CF. H2B ubiquitylation and the histone chaperone Asf1 cooperatively mediate the formation and maintenance of heterochromatin silencing. Nucleic Acids Res 2017; 45:8225-8238. [PMID: 28520954 PMCID: PMC5737242 DOI: 10.1093/nar/gkx422] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Accepted: 05/03/2017] [Indexed: 11/24/2022] Open
Abstract
Heterochromatin is a heritable form of gene repression, with critical roles in development and cell identity. Understanding how chromatin factors results in such repression is a fundamental question. Chromatin is assembled and disassembled during transcription, replication and repair by anti-silencing function 1 (Asf1), a highly conserved histone chaperone. Transcription and DNA replication are also affected by histone modifications that modify nucleosome dynamics, such as H2B ubiquitylation (H2Bub). We report here that H2Bub and Asf1 cooperatively promote transcriptional silencing at yeast telomeres and mating loci. Through real time monitoring of HML (Hidden MAT Left) locus silencing, we found that transcriptional repression was slowly initiated and never fully established in mutants lacking both Asf1 and H2Bub. These findings are consistent with impaired HML silencer-binding and spreading of repressor proteins, Sir2 and Sir3. In addition, mutants lacking H2Bub and Asf1 show defects in both nucleosome assembly and higher-order heterochromatin organization at the HML locus. Our findings reveal a novel role for H2Bub and Asf1 in epigenetic silencing at mating loci. Thus, the interplay between H2Hbub and Asf1 may fine-tune nucleosome dynamics and SIR protein recruitment, and represent an ongoing requirement for proper formation and maintenance of heterochromatin.
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Affiliation(s)
- Meng-Ying Wu
- Institute of Cellular and Organismic Biology, Academia Sinica, 128, Academia Road, Section 2, Nankang, Taipei 11529, Taiwan
| | - Chia-Yeh Lin
- Institute of Cellular and Organismic Biology, Academia Sinica, 128, Academia Road, Section 2, Nankang, Taipei 11529, Taiwan
| | - Hsin-Yi Tseng
- Institute of Cellular and Organismic Biology, Academia Sinica, 128, Academia Road, Section 2, Nankang, Taipei 11529, Taiwan
| | - Fei-Man Hsu
- Institute of Plant and Microbial Biology, Academia Sinica, 128, Academia Road, Section 2, Nankang, Taipei 11529, Taiwan
| | - Pao-Yang Chen
- Institute of Plant and Microbial Biology, Academia Sinica, 128, Academia Road, Section 2, Nankang, Taipei 11529, Taiwan
| | - Cheng-Fu Kao
- Institute of Cellular and Organismic Biology, Academia Sinica, 128, Academia Road, Section 2, Nankang, Taipei 11529, Taiwan
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13
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Wyse B, Oshidari R, Rowlands H, Abbasi S, Yankulov K. RRM3 regulates epigenetic conversions in Saccharomyces cerevisiae in conjunction with Chromatin Assembly Factor I. Nucleus 2017; 7:405-14. [PMID: 27645054 DOI: 10.1080/19491034.2016.1212796] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Chromatin structures are transmitted to daughter cells through a complex system of nucleosome disassembly and re-assembly at the advancing replication forks. However, the role of replication pausing in the transmission and perturbation of chromatin structures has not been addressed. RRM3 encodes a DNA helicase, which facilitates replication at sites covered with non-histone protein complexes (tRNA genes, active gene promoters, telomeres) in Saccharomyces cerevisiae. In this report we show that the deletion of RRM3 reduces the frequency of epigenetic conversions in the subtelomeric regions of the chromosomes. This phenotype is strongly dependent on 2 histone chaperones, CAF-I and ASF1, which are involved in the reassembly of nucleosomes behind replication forks, but not on the histone chaperone HIR1. We also show that the deletion of RRM3 increases the spontaneous mutation rates in conjunction with CAF-I and ASF1, but not HIR1. Finally, we demonstrate that Rrm3p and CAF-I compete for the binding to the DNA replication clamp PCNA (Proliferating Cell Nuclear Antigen). We propose that the stalling of DNA replication predisposes to epigenetic conversions and that RRM3 and CAF-I play key roles in this process.
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Affiliation(s)
- Brandon Wyse
- a Department of Molecular and Cellular Biology , University of Guelph , Ontario , Canada
| | - Roxanne Oshidari
- a Department of Molecular and Cellular Biology , University of Guelph , Ontario , Canada
| | - Hollie Rowlands
- a Department of Molecular and Cellular Biology , University of Guelph , Ontario , Canada
| | - Sanna Abbasi
- a Department of Molecular and Cellular Biology , University of Guelph , Ontario , Canada
| | - Krassimir Yankulov
- a Department of Molecular and Cellular Biology , University of Guelph , Ontario , Canada
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14
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Mattiroli F, Gu Y, Yadav T, Balsbaugh JL, Harris MR, Findlay ES, Liu Y, Radebaugh CA, Stargell LA, Ahn NG, Whitehouse I, Luger K. DNA-mediated association of two histone-bound complexes of yeast Chromatin Assembly Factor-1 (CAF-1) drives tetrasome assembly in the wake of DNA replication. eLife 2017; 6:e22799. [PMID: 28315523 PMCID: PMC5404915 DOI: 10.7554/elife.22799] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Accepted: 03/14/2017] [Indexed: 12/13/2022] Open
Abstract
Nucleosome assembly in the wake of DNA replication is a key process that regulates cell identity and survival. Chromatin assembly factor 1 (CAF-1) is a H3-H4 histone chaperone that associates with the replisome and orchestrates chromatin assembly following DNA synthesis. Little is known about the mechanism and structure of this key complex. Here we investigate the CAF-1•H3-H4 binding mode and the mechanism of nucleosome assembly. We show that yeast CAF-1 binding to a H3-H4 dimer activates the Cac1 winged helix domain interaction with DNA. This drives the formation of a transient CAF-1•histone•DNA intermediate containing two CAF-1 complexes, each associated with one H3-H4 dimer. Here, the (H3-H4)2 tetramer is formed and deposited onto DNA. Our work elucidates the molecular mechanism for histone deposition by CAF-1, a reaction that has remained elusive for other histone chaperones, and it advances our understanding of how nucleosomes and their epigenetic information are maintained through DNA replication.
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Affiliation(s)
- Francesca Mattiroli
- Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Colorado Boulder, Boulder, United States
| | - Yajie Gu
- Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Colorado Boulder, Boulder, United States
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, United States
| | - Tejas Yadav
- Weill Cornell Graduate School of Medical Sciences, New York, United States
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Jeremy L Balsbaugh
- Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, United States
| | - Michael R Harris
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Eileen S Findlay
- Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Colorado Boulder, Boulder, United States
| | - Yang Liu
- Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Colorado Boulder, Boulder, United States
| | - Catherine A Radebaugh
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, United States
| | - Laurie A Stargell
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, United States
- Institute for Genome Architecture and Function, Colorado State University, Fort Collins, United States
| | - Natalie G Ahn
- Biofrontiers Institute, University of Colorado Boulder, Boulder, United States
| | - Iestyn Whitehouse
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Karolin Luger
- Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Colorado Boulder, Boulder, United States
- Institute for Genome Architecture and Function, Colorado State University, Fort Collins, United States
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15
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O-linked N-acetylglucosamine transferase (OGT) interacts with the histone chaperone HIRA complex and regulates nucleosome assembly and cellular senescence. Proc Natl Acad Sci U S A 2016; 113:E3213-20. [PMID: 27217568 DOI: 10.1073/pnas.1600509113] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The histone chaperone HIRA complex, consisting of histone cell cycle regulator (HIRA), Ubinuclein1 (UBN1), and calcineurin binding protein 1 (CABIN1), deposits histone variant H3.3 to genic regions and regulates gene expression in various cellular processes, including cellular senescence. How HIRA-mediated nucleosome assembly of H3.3-H4 is regulated remains not well understood. Here, we show that O-linked N-acetylglucosamine (GlcNAc) transferase (OGT), an enzyme that catalyzes O-GlcNAcylation of serine or threonine residues, interacts with UBN1, modifies HIRA, and promotes nucleosome assembly of H3.3. Depletion of OGT or expression of the HIRA S231A O-GlcNAcylation-deficient mutant compromises formation of the HIRA-H3.3 complex and H3.3 nucleosome assembly. Importantly, OGT depletion or expression of the HIRA S231A mutant delays premature cellular senescence in primary human fibroblasts, whereas overexpression of OGT accelerates senescence. Taken together, these results support a model in which OGT modifies HIRA to regulate HIRA-H3.3 complex formation and H3.3 nucleosome assembly and reveal the mechanism by which OGT functions in cellular senescence.
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16
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Evolution of Robustness to Protein Mistranslation by Accelerated Protein Turnover. PLoS Biol 2015; 13:e1002291. [PMID: 26544557 PMCID: PMC4636289 DOI: 10.1371/journal.pbio.1002291] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Accepted: 09/30/2015] [Indexed: 11/19/2022] Open
Abstract
Translational errors occur at high rates, and they influence organism viability and the onset of genetic diseases. To investigate how organisms mitigate the deleterious effects of protein synthesis errors during evolution, a mutant yeast strain was engineered to translate a codon ambiguously (mistranslation). It thereby overloads the protein quality-control pathways and disrupts cellular protein homeostasis. This strain was used to study the capacity of the yeast genome to compensate the deleterious effects of protein mistranslation. Laboratory evolutionary experiments revealed that fitness loss due to mistranslation can rapidly be mitigated. Genomic analysis demonstrated that adaptation was primarily mediated by large-scale chromosomal duplication and deletion events, suggesting that errors during protein synthesis promote the evolution of genome architecture. By altering the dosages of numerous, functionally related proteins simultaneously, these genetic changes introduced large phenotypic leaps that enabled rapid adaptation to mistranslation. Evolution increased the level of tolerance to mistranslation through acceleration of ubiquitin-proteasome–mediated protein degradation and protein synthesis. As a consequence of rapid elimination of erroneous protein products, evolution reduced the extent of toxic protein aggregation in mistranslating cells. However, there was a strong evolutionary trade-off between adaptation to mistranslation and survival upon starvation: the evolved lines showed fitness defects and impaired capacity to degrade mature ribosomes upon nutrient limitation. Moreover, as a response to an enhanced energy demand of accelerated protein turnover, the evolved lines exhibited increased glucose uptake by selective duplication of hexose transporter genes. We conclude that adjustment of proteome homeostasis to mistranslation evolves rapidly, but this adaptation has several side effects on cellular physiology. Our work also indicates that translational fidelity and the ubiquitin-proteasome system are functionally linked to each other and may, therefore, co-evolve in nature. Tolerance to errors during protein synthesis evolves rapidly through acceleration of protein turnover—a process determined by the combined rates of protein synthesis and degradation. However, this adaptation has deleterious side effects due to its energy costs. Although fidelity of information transfer has a substantial impact on cellular survival, many steps in protein production are strikingly error-prone. Such errors during protein synthesis can have a substantial influence on viability and the onset of genetic diseases. These considerations raise the question as to how organisms can tolerate errors during protein synthesis. In this paper, for the first time, we study organisms’ capacity to evolve robustness against mistranslation and explore the underlying cellular mechanisms. A mutant yeast strain was engineered to translate a codon ambiguously (mistranslation). This thereby overloads the protein quality-control pathways and disrupts cellular protein homeostasis. This strain was used to study the capacity of the yeast genome to compensate for the deleterious effects of protein mistranslation. We found that mistranslation led to rapid evolution of genomic rearrangements, including chromosomal duplications and deletions. By altering the dosages of numerous, functionally related proteins simultaneously, these genetic changes introduce large phenotypic leaps that enable adaptation to mistranslation. Robustness against mistranslation during laboratory evolution was achieved through acceleration of protein turnover—a process that was determined by the combined rates of protein synthesis and ubiquitin-proteasome system-mediated degradation. However, as both translation and active degradation of proteins are exceptionally energy-consuming cellular processes, accelerated proteome turnover has substantial energy costs.
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17
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Jeffery DCB, Kakusho N, You Z, Gharib M, Wyse B, Drury E, Weinreich M, Thibault P, Verreault A, Masai H, Yankulov K. CDC28 phosphorylates Cac1p and regulates the association of chromatin assembly factor I with chromatin. Cell Cycle 2015; 14:74-85. [PMID: 25602519 DOI: 10.4161/15384101.2014.973745] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Chromatin Assembly Factor I (CAF-I) plays a key role in the replication-coupled assembly of nucleosomes. It is expected that its function is linked to the regulation of the cell cycle, but little detail is available. Current models suggest that CAF-I is recruited to replication forks and to chromatin via an interaction between its Cac1p subunit and the replication sliding clamp, PCNA, and that this interaction is stimulated by the kinase CDC7. Here we show that another kinase, CDC28, phosphorylates Cac1p on serines 94 and 515 in early S phase and regulates its association with chromatin, but not its association with PCNA. Mutations in the Cac1p-phosphorylation sites of CDC28 but not of CDC7 substantially reduce the in vivo phosphorylation of Cac1p. However, mutations in the putative CDC7 target sites on Cac1p reduce its stability. The association of CAF-I with chromatin is impaired in a cdc28-1 mutant and to a lesser extent in a cdc7-1 mutant. In addition, mutations in the Cac1p-phosphorylation sites by both CDC28 and CDC7 reduce gene silencing at the telomeres. We propose that this phosphorylation represents a regulatory step in the recruitment of CAF-I to chromatin in early S phase that is distinct from the association of CAF-I with PCNA. Hence, we implicate CDC28 in the regulation of chromatin reassembly during DNA replication. These findings provide novel mechanistic insights on the links between cell-cycle regulation, DNA replication and chromatin reassembly.
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Affiliation(s)
- Daniel C B Jeffery
- a Department of Molecular and Cellular Biology ; University of Guelph ; Guelph , Ontario , Canada
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18
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Dvořáčková M, Fojtová M, Fajkus J. Chromatin dynamics of plant telomeres and ribosomal genes. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2015; 83:18-37. [PMID: 25752316 DOI: 10.1111/tpj.12822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Revised: 03/03/2015] [Accepted: 03/03/2015] [Indexed: 05/03/2023]
Abstract
Telomeres and genes encoding 45S ribosomal RNA (rDNA) are frequently located adjacent to each other on eukaryotic chromosomes. Although their primary roles are different, they show striking similarities with respect to their features and additional functions. Both genome domains have remarkably dynamic chromatin structures. Both are hypersensitive to dysfunctional histone chaperones, responding at the genomic and epigenomic levels. Both generate non-coding transcripts that, in addition to their epigenetic roles, may induce gross chromosomal rearrangements. Both give rise to chromosomal fragile sites, as their replication is intrinsically problematic. However, at the same time, both are essential for maintenance of genomic stability and integrity. Here we discuss the structural and functional inter-connectivity of telomeres and rDNA, with a focus on recent results obtained in plants.
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Affiliation(s)
- Martina Dvořáčková
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Kamenice 5, 62500, Brno, Czech Republic
- Faculty of Science, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, 61265, Brno, Czech Republic
| | - Miloslava Fojtová
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Kamenice 5, 62500, Brno, Czech Republic
- Faculty of Science, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, 61265, Brno, Czech Republic
| | - Jiří Fajkus
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Kamenice 5, 62500, Brno, Czech Republic
- Faculty of Science, Masaryk University, Kamenice 5, 62500, Brno, Czech Republic
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, 61265, Brno, Czech Republic
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19
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Duc C, Benoit M, Le Goff S, Simon L, Poulet A, Cotterell S, Tatout C, Probst AV. The histone chaperone complex HIR maintains nucleosome occupancy and counterbalances impaired histone deposition in CAF-1 complex mutants. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2015; 81:707-22. [PMID: 25600486 DOI: 10.1111/tpj.12758] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Revised: 11/21/2014] [Accepted: 12/23/2014] [Indexed: 05/09/2023]
Abstract
Chromatin organization is essential for coordinated gene expression, genome stability, and inheritance of epigenetic information. The main components involved in chromatin assembly are specific complexes such as Chromatin Assembly Factor 1 (CAF-1) and Histone Regulator (HIR), which deposit histones in a DNA synthesis-dependent or -independent manner, respectively. Here, we characterize the role of the plant orthologs Histone Regulator A (HIRA), Ubinuclein (UBN) and Calcineurin Binding protein 1 (CABIN1), which constitute the HIR complex. Arabidopsis loss-of-function mutants for the various subunits of the complex are viable, but hira mutants show reduced fertility. We show that loss of HIRA reduces extractable histone H3 protein levels and decreases nucleosome occupancy at both actively transcribed genes and heterochromatic regions. Concomitantly, HIRA contributes to maintenance of silencing of pericentromeric repeats and certain transposons. A genetic analysis based on crosses between mutants deficient in subunits of the CAF-1 and HIR complexes showed that simultaneous loss of both the CAF-1 and HIR histone H3 chaperone complexes severely affects plant survival, growth and reproductive development. Our results suggest that HIRA partially rescues impaired histone deposition in fas mutants to preserve nucleosome occupancy, implying plasticity in histone variant interaction and deposition.
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Affiliation(s)
- Céline Duc
- Génétique, Reproduction et Développement, CNRS UMR 6293, Clermont Université, INSERM U1103, 24 Avenue des Landais, BP 80026, Aubière Cedex, 63171, France
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20
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Gurard-Levin ZA, Quivy JP, Almouzni G. Histone chaperones: assisting histone traffic and nucleosome dynamics. Annu Rev Biochem 2015; 83:487-517. [PMID: 24905786 DOI: 10.1146/annurev-biochem-060713-035536] [Citation(s) in RCA: 213] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The functional organization of eukaryotic DNA into chromatin uses histones as components of its building block, the nucleosome. Histone chaperones, which are proteins that escort histones throughout their cellular life, are key actors in all facets of histone metabolism; they regulate the supply and dynamics of histones at chromatin for its assembly and disassembly. Histone chaperones can also participate in the distribution of histone variants, thereby defining distinct chromatin landscapes of importance for genome function, stability, and cell identity. Here, we discuss our current knowledge of the known histone chaperones and their histone partners, focusing on histone H3 and its variants. We then place them into an escort network that distributes these histones in various deposition pathways. Through their distinct interfaces, we show how they affect dynamics during DNA replication, DNA damage, and transcription, and how they maintain genome integrity. Finally, we discuss the importance of histone chaperones during development and describe how misregulation of the histone flow can link to disease.
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Affiliation(s)
- Zachary A Gurard-Levin
- Institut Curie, Centre de Recherche; CNRS UMR 3664; Equipe Labellisée, Ligue contre le Cancer; and Université Pierre et Marie Curie, Paris F-75248, France;
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21
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Knapp AR, Wang H, Parthun MR. The yeast histone chaperone hif1p functions with RNA in nucleosome assembly. PLoS One 2014; 9:e100299. [PMID: 25072697 PMCID: PMC4114455 DOI: 10.1371/journal.pone.0100299] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Accepted: 05/22/2014] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Hif1p is an H3/H4-specific histone chaperone that associates with the nuclear form of the Hat1p/Hat2p complex (NuB4 complex) in the yeast Saccharomyces cerevisiae. While not capable of depositing histones onto DNA on its own, Hif1p can act in conjunction with a yeast cytosolic extract to assemble nucleosomes onto a relaxed circular plasmid. RESULTS To identify the factor(s) that function with Hif1p to carry out chromatin assembly, multiple steps of column chromatography were carried out to fractionate the yeast cytosolic extract. Analysis of partially purified fractions indicated that Hif1p-dependent chromatin assembly activity resided in RNA rather than protein. Fractionation of isolated RNA indicated that the chromatin assembly activity did not simply purify with bulk RNA. In addition, the RNA-mediated chromatin assembly activity was blocked by mutations in the human homolog of Hif1p, sNASP, that prevent the association of this histone chaperone with histone H3 and H4 without altering its electrostatic properties. CONCLUSIONS These results suggest that specific RNA species may function in concert with histone chaperones to assemble chromatin.
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Affiliation(s)
- Amy R. Knapp
- Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, Ohio, United States of America
| | - Huanyu Wang
- Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, Ohio, United States of America
| | - Mark R. Parthun
- Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, Ohio, United States of America
- * E-mail:
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22
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Singh J. Role of DNA replication in establishment and propagation of epigenetic states of chromatin. Semin Cell Dev Biol 2014; 30:131-43. [PMID: 24794003 DOI: 10.1016/j.semcdb.2014.04.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Accepted: 04/03/2014] [Indexed: 10/25/2022]
Abstract
DNA replication is the fundamental process of duplication of the genetic information that is vital for survival of all living cells. The basic mechanistic steps of replication initiation, elongation and termination are conserved among bacteria, lower eukaryotes, like yeast and metazoans. However, the details of the mechanisms are different. Furthermore, there is a close coordination between chromatin assembly pathways and various components of replication machinery whereby DNA replication is coupled to "chromatin replication" during cell cycle. Thereby, various epigenetic modifications associated with different states of gene expression in differentiated cells and the related chromatin structures are faithfully propagated during the cell division through tight coupling with the DNA replication machinery. Several examples are found in lower eukaryotes like budding yeast and fission yeast with close parallels in metazoans.
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Affiliation(s)
- Jagmohan Singh
- CSIR-Institute of Microbial Technology, Sector 39A, Chandigarh, India.
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23
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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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24
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Amin AD, Vishnoi N, Prochasson P. A global requirement for the HIR complex in the assembly of chromatin. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2014; 1819:264-276. [PMID: 24459729 DOI: 10.1016/j.bbagrm.2011.07.008] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Due to its extensive length, DNA is packaged into a protective chromatin structure known as the nucleosome. In order to carry out various cellular functions, nucleosomes must be disassembled, allowing access to the underlying DNA, and subsequently reassembled on completion of these processes. The assembly and disassembly of nucleosomes is dependent on the function of histone modifiers, chromatin remodelers and histone chaperones. In this review, we discuss the roles of an evolutionarily conserved histone chaperone known as the HIR/HIRA complex. In S. cerevisiae, the HIR complex is made up of the proteins Hir1, Hir2, Hir3 and Hpc2, which collectively act in transcriptional regulation, elongation, gene silencing, cellular senescence and even aging. This review presents an overview of the role of the HIR complex, in yeast as well as other organisms, in each of these processes, in order to give a better understanding of how nucleosome assembly is imperative for cellular homeostasis and genomic integrity. This article is part of a Special Issue entitled: Histone chaperones and Chromatin assembly.
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25
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Annunziato AT. Assembling chromatin: the long and winding road. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2014; 1819:196-210. [PMID: 24459722 DOI: 10.1016/j.bbagrm.2011.07.005] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
It has been over 35 years since the acceptance of the "chromatin subunit" hypothesis, and the recognition that nucleosomes are the fundamental repeating units of chromatin fibers. Major subjects of inquiry in the intervening years have included the steps involved in chromatin assembly, and the chaperones that escort histones to DNA. The following commentary offers an historical perspective on inquiries into the processes by which nucleosomes are assembled on replicating and nonreplicating chromatin. This article is part of a Special Issue entitled: Histone chaperones and Chromatin assembly.
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26
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A saccharomyces cerevisiae RNase H2 interaction network functions to suppress genome instability. Mol Cell Biol 2014; 34:1521-34. [PMID: 24550002 DOI: 10.1128/mcb.00960-13] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Errors during DNA replication are one likely cause of gross chromosomal rearrangements (GCRs). Here, we analyze the role of RNase H2, which functions to process Okazaki fragments, degrade transcription intermediates, and repair misincorporated ribonucleotides, in preventing genome instability. The results demonstrate that rnh203 mutations result in a weak mutator phenotype and cause growth defects and synergistic increases in GCR rates when combined with mutations affecting other DNA metabolism pathways, including homologous recombination (HR), sister chromatid HR, resolution of branched HR intermediates, postreplication repair, sumoylation in response to DNA damage, and chromatin assembly. In some cases, a mutation in RAD51 or TOP1 suppressed the increased GCR rates and/or the growth defects of rnh203Δ double mutants. This analysis suggests that cells with RNase H2 defects have increased levels of DNA damage and depend on other pathways of DNA metabolism to overcome the deleterious effects of this DNA damage.
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27
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Han J, Zhang H, Zhang H, Wang Z, Zhou H, Zhang Z. A Cul4 E3 ubiquitin ligase regulates histone hand-off during nucleosome assembly. Cell 2014; 155:817-29. [PMID: 24209620 DOI: 10.1016/j.cell.2013.10.014] [Citation(s) in RCA: 103] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2012] [Revised: 05/12/2013] [Accepted: 10/01/2013] [Indexed: 10/26/2022]
Abstract
Nucleosome assembly following DNA replication and gene transcription is important to maintain genome stability and epigenetic information. Newly synthesized histones H3-H4 first bind histone chaperone Asf1 and are then transferred to other chaperones for nucleosome assembly. However, it is unknown how H3-H4 is transferred from the Asf1-H3-H4 complex to other chaperones because Asf1 binds H3-H4 with high affinity. Here, we show that yeast Rtt101(Mms1) E3 ubiquitin ligase preferentially binds and ubiquitylates new histone H3 acetylated at lysine 56. Inactivation of Rtt101 or mutating H3 lysine residues ubiquitylated by the Rtt101(Mms1) ligase impairs nucleosome assembly and promotes Asf1-H3 interactions. Similar phenotypes occur in human cells in which the ortholog of Rtt101(Mms1), Cul4A(DDB1), is depleted. These results indicate that the transfer of H3-H4 from the Asf1-H3-H4 complex to other histone chaperones is regulated by a conserved E3 ligase and provide evidence for crosstalk between histone acetylation and ubiquitylation in nucleosome assembly.
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Affiliation(s)
- Junhong Han
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA
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28
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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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Nucleosome assembly factors CAF-1 and HIR modulate epigenetic switching frequencies in an H3K56 acetylation-associated manner in Candida albicans. EUKARYOTIC CELL 2013; 12:591-603. [PMID: 23417560 DOI: 10.1128/ec.00334-12] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
CAF-1 and HIR are highly conserved histone chaperone protein complexes that function in the assembly of nucleosomes onto chromatin. CAF-1 is characterized as having replication-coupled nucleosome activity, whereas the HIR complex can assemble nucleosomes independent of replication. Histone H3K56 acetylation, controlled by the acetyltransferase Rtt109 and deacetylase Hst3, also plays a significant role in nucleosome assembly. In this study, we generated a set of deletion mutants to genetically characterize pathway-specific and overlapping functions of CAF-1 and HIR in C. albicans. Their roles in epigenetic maintenance of cell type were examined by using the white-opaque switching system in C. albicans. We show that CAF-1 and HIR play conserved roles in UV radiation recovery, repression of histone gene expression, correct chromosome segregation, and stress responses. Unique to C. albicans, the cac2Δ/Δ mutant shows increased sensitivity to the Hst3 inhibitor nicotinamide, while the rtt109Δ/Δ cac2Δ/Δ and hir1Δ/Δ cac2Δ/Δ mutants are resistant to nicotinamide. CAF-1 plays a major role in maintaining cell types, as the cac2Δ/Δ mutant exhibited increased switching frequencies in both directions and switched at a high frequency to opaque in response to nicotinamide. Like the rtt109Δ/Δ mutant, the hir1Δ/Δ cac2Δ/Δ double mutant is defective in maintaining the opaque cell fate and blocks nicotinamide-induced opaque formation, and the defects are suppressed by ectopic expression of the master white-opaque regulator Wor1. Our data suggest an overlapping function of CAF-1 and HIR in epigenetic regulation of cell fate determination in an H3K56 acetylation-associated manner.
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The C terminus of the histone chaperone Asf1 cross-links to histone H3 in yeast and promotes interaction with histones H3 and H4. Mol Cell Biol 2012. [PMID: 23184661 DOI: 10.1128/mcb.01053-12] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The central histone H3/H4 chaperone Asf1 comprises a highly conserved globular core and a divergent C-terminal tail. While the function and structure of the Asf1 core are well known, the function of the tail is less well understood. Here, we have explored the role of the yeast (yAsf1) and human (hAsf1a and hAsf1b) Asf1 tails in Saccharomyces cerevisiae. We show, using a photoreactive, unnatural amino acid, that Asf1 tail residue 210 cross-links to histone H3 in vivo and, further, that loss of C-terminal tail residues 211 to 279 weakens yAsf1-histone binding affinity in vitro nearly 200-fold. Via several yAsf1 C-terminal truncations and yeast-human chimeric proteins, we found that truncations at residue 210 increase transcriptional silencing and that the hAsf1a tail partially substitutes for full-length yAsf1 with respect to silencing but that full-length hAsf1b is a better overall substitute for full-length yAsf1. In addition, we show that the C-terminal tail of Asf1 is phosphorylated at T270 in yeast. Loss of this phosphorylation site does not prevent coimmunoprecipitation of yAsf1 and Rad53 from yeast extracts, whereas amino acid residue substitutions at the Asf1-histone H3/H4 interface do. Finally, we show that residue substitutions in yAsf1 near the CAF-1/HIRA interface also influence yAsf1's function in silencing.
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Direct interplay among histones, histone chaperones, and a chromatin boundary protein in the control of histone gene expression. Mol Cell Biol 2012; 32:4337-49. [PMID: 22907759 DOI: 10.1128/mcb.00871-12] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In Saccharomyces cerevisiae, the histone chaperone Rtt106 binds newly synthesized histone proteins and mediates their delivery into chromatin during transcription, replication, and silencing. Rtt106 is also recruited to histone gene regulatory regions by the HIR histone chaperone complex to ensure S-phase-specific expression. Here we showed that this Rtt106:HIR complex included Asf1 and histone proteins. Mutations in Rtt106 that reduced histone binding reduced Rtt106 enrichment at histone genes, leading to their increased transcription. Deletion of the chromatin boundary element Yta7 led to increased Rtt106:H3 binding, increased Rtt106 enrichment at histone gene regulatory regions, and decreased histone gene transcription at the HTA1-HTB1 locus. These results suggested a unique regulatory mechanism in which Rtt106 sensed the level of histone proteins to maintain the proper level of histone gene transcription. The role of these histone chaperones and Yta7 differed markedly among the histone gene loci, including the two H3-H4 histone gene pairs. Defects in silencing in rtt106 mutants could be partially accounted for by Rtt106-mediated changes in histone gene repression. These studies suggested that feedback mediated by histone chaperone complexes plays a pivotal role in regulating histone gene transcription.
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32
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H2B Tyr37 phosphorylation suppresses expression of replication-dependent core histone genes. Nat Struct Mol Biol 2012; 19:930-7. [PMID: 22885324 DOI: 10.1038/nsmb.2356] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Accepted: 07/09/2012] [Indexed: 01/12/2023]
Abstract
Histone gene transcription is actively downregulated after completion of DNA synthesis to avoid overproduction. However, the precise mechanistic details of the cessation of histone mRNA synthesis are not clear. We found that histone H2B phosphorylation at Tyr37 occurs upstream of histone cluster 1, Hist1, during the late S phase. We identified WEE1 as the kinase that phosphorylates H2B at Tyr37. Loss of expression or inhibition of WEE1 kinase abrogated H2B Tyr37 phosphorylation with a concomitant increase in histone transcription in yeast and mammalian cells. H2B Tyr37 phosphorylation excluded binding of the transcriptional coactivator NPAT and RNA polymerase II and recruited the histone chaperone HIRA upstream of the Hist1 cluster. Taken together, our data show a previously unknown and evolutionarily conserved function for WEE1 kinase as an epigenetic modulator that marks chromatin with H2B Tyr37 phosphorylation, thereby inhibiting the transcription of multiple histone genes to lower the burden on the histone mRNA turnover machinery.
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Schizosaccharomyces pombe Hat1 (Kat1) is associated with Mis16 and is required for telomeric silencing. EUKARYOTIC CELL 2012; 11:1095-103. [PMID: 22771823 DOI: 10.1128/ec.00123-12] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The Hat1 histone acetyltransferase has been implicated in the acetylation of histone H4 during chromatin assembly. In this study, we have characterized the Hat1 complex from the fission yeast Schizosaccharomyces pombe and have examined its role in telomeric silencing. Hat1 is found associated with the RbAp46 homologue Mis16, an essential protein. The Hat1 complex acetylates lysines 5 and 12 of histone H4, the sites that are acetylated in newly synthesized H4 in a wide range of eukaryotes. Deletion of hat1 in S. pombe is itself sufficient to cause the loss of silencing at telomeres. This is in contrast to results obtained with an S. cerevisiae hat1Δ strain, which must also carry mutations of specific acetylatable lysines in the H3 tail domain for loss of telomeric silencing to occur. Notably, deletion of hat1 from S. pombe resulted in an increase of acetylation of histone H4 in subtelomeric chromatin, concomitant with derepression of this region. A similar loss of telomeric silencing was also observed after growing cells in the presence of the deacetylase inhibitor trichostatin A. However, deleting hat1 did not cause loss of silencing at centromeres or the silent mating type locus. These results point to a direct link between Hat1, H4 acetylation, and the establishment of repressed telomeric chromatin in fission yeast.
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Abstract
Understanding the mechanisms by which chromatin structure controls eukaryotic transcription has been an intense area of investigation for the past 25 years. Many of the key discoveries that created the foundation for this field came from studies of Saccharomyces cerevisiae, including the discovery of the role of chromatin in transcriptional silencing, as well as the discovery of chromatin-remodeling factors and histone modification activities. Since that time, studies in yeast have continued to contribute in leading ways. This review article summarizes the large body of yeast studies in this field.
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Sarkies P, Sale JE. Propagation of histone marks and epigenetic memory during normal and interrupted DNA replication. Cell Mol Life Sci 2012; 69:697-716. [PMID: 21964926 PMCID: PMC11114753 DOI: 10.1007/s00018-011-0824-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Revised: 09/02/2011] [Accepted: 09/12/2011] [Indexed: 11/30/2022]
Abstract
Although all nucleated cells within a multicellular organism contain a complete copy of the genome, cell identity relies on the expression of a specific subset of genes. Therefore, when cells divide they must not only copy their genome to their daughters, but also ensure that the pattern of gene expression present before division is restored. While the carrier of this epigenetic memory has been a topic of much research and debate, post-translational modifications of histone proteins have emerged in the vanguard of candidates. In this paper we examine the mechanisms by which histone post-translational modifications are propagated through DNA replication and cell division, and we critically examine the evidence that they can also act as vectors of epigenetic memory. Finally, we consider ways in which epigenetic memory might be disrupted by interfering with the mechanisms of DNA replication.
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Affiliation(s)
- Peter Sarkies
- Division of Protein and Nucleic Acid Chemistry, Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 0QH UK
| | - Julian E. Sale
- Division of Protein and Nucleic Acid Chemistry, Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 0QH UK
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Li Q, Zhang Z. Linking DNA replication to heterochromatin silencing and epigenetic inheritance. Acta Biochim Biophys Sin (Shanghai) 2012; 44:3-13. [PMID: 22194009 DOI: 10.1093/abbs/gmr107] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Chromatin is organized into distinct functional domains. During mitotic cell division, both genetic information encoded in DNA sequence and epigenetic information embedded in chromatin structure must be faithfully duplicated. The inheritance of epigenetic states is critical in maintaining the genome integrity and gene expression state. In this review, we will discuss recent progress on how proteins known to be involved in DNA replication and DNA replication-coupled nucleosome assembly impact on the inheritance and maintenance of heterochromatin, a tightly compact chromatin structure that silences gene transcription. As heterochromatin is important in regulating gene expression and maintaining genome stability, understanding how heterochromatin states are inherited during S phase of the cell cycle is of fundamental importance.
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Simboeck E, Ribeiro JD, Teichmann S, Di Croce L. Epigenetics and senescence: Learning from the INK4-ARF locus. Biochem Pharmacol 2011; 82:1361-70. [DOI: 10.1016/j.bcp.2011.07.084] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2011] [Revised: 07/14/2011] [Accepted: 07/15/2011] [Indexed: 11/30/2022]
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38
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Moazed D. Mechanisms for the inheritance of chromatin states. Cell 2011; 146:510-8. [PMID: 21854979 DOI: 10.1016/j.cell.2011.07.013] [Citation(s) in RCA: 168] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2011] [Revised: 06/20/2011] [Accepted: 07/13/2011] [Indexed: 12/24/2022]
Abstract
Studies in eukaryotes ranging from yeast to mammals indicate that specific chromatin structures can be inherited following DNA replication via mechanisms acting in cis. Both the initial establishment of such chromatin structures and their inheritance require sequence-dependent specificity factors and changes in histone posttranslational modifications. Here I propose models for the maintenance of epigenetic information in which DNA silencers or nascent RNA scaffolds act as sensors that work cooperatively with parentally inherited histones to re-establish chromatin states following DNA replication.
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Affiliation(s)
- Danesh Moazed
- Howard Hughes Medical Institute, Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
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39
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Palmitoylation controls the dynamics of budding-yeast heterochromatin via the telomere-binding protein Rif1. Proc Natl Acad Sci U S A 2011; 108:14572-7. [PMID: 21844336 DOI: 10.1073/pnas.1105262108] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The posttranslational addition of palmitate to cysteines occurs ubiquitously in eukaryotic cells, where it functions in anchoring target proteins to membranes and in vesicular trafficking. Here we show that the Saccharomyces cerevisiae palmitoyltransferase Pfa4 enhanced heterochromatin formation at the cryptic mating-type loci HMR and HML via Rif1, a telomere regulatory protein. Acylated Rif1 was detected in extracts from wild-type but not pfa4Δ mutant cells. In a pfa4Δ mutant, Rif1-GFP dispersed away from foci positioned at the nuclear periphery into the nucleoplasm. Sir3-GFP distribution was also perturbed, indicating a change in the nuclear dynamics of heterochromatin proteins. Genetic analyses indicated that PFA4 functioned upstream of RIF1. Surprisingly, the pfa4Δ mutation had only mild effects on telomeric regulation, suggesting Rif1's roles at HM loci and telomeres were more complexly related than previously thought. These data supported a model in which Pfa4-dependent palmitoylation of Rif1 anchored it to the inner nuclear membrane, influencing its role in heterochromatin dynamics.
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40
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The specificity and topology of chromatin interaction pathways in yeast. Mol Cell 2011; 42:536-49. [PMID: 21596317 DOI: 10.1016/j.molcel.2011.03.026] [Citation(s) in RCA: 197] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2010] [Revised: 01/12/2011] [Accepted: 03/18/2011] [Indexed: 01/07/2023]
Abstract
Packaging of DNA into chromatin has a profound impact on gene expression. To understand how changes in chromatin influence transcription, we analyzed 165 mutants of chromatin machinery components in Saccharomyces cerevisiae. mRNA expression patterns change in 80% of mutants, always with specific effects, even for loss of widespread histone marks. The data are assembled into a network of chromatin interaction pathways. The network is function based, has a branched, interconnected topology, and lacks strict one-to-one relationships between complexes. Chromatin pathways are not separate entities for different gene sets, but share many components. The study evaluates which interactions are important for which genes and predicts additional interactions, for example between Paf1C and Set3C, as well as a role for Mediator in subtelomeric silencing. The results indicate the presence of gene-dependent effects that go beyond context-dependent binding of chromatin factors and provide a framework for understanding how specificity is achieved through regulating chromatin.
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Rai TS, Adams PD. Lessons from senescence: Chromatin maintenance in non-proliferating cells. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2011; 1819:322-31. [PMID: 21839870 DOI: 10.1016/j.bbagrm.2011.07.014] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Revised: 07/25/2011] [Accepted: 07/27/2011] [Indexed: 02/08/2023]
Abstract
Cellular senescence is an irreversible proliferation arrest, thought to contribute to tumor suppression, proper wound healing and, perhaps, tissue and organismal aging. Two classical tumor suppressors, p53 and pRB, control cell cycle arrest associated with senescence. Profound molecular changes occur in cells undergoing senescence. At the level of chromatin, for example, senescence associated heterochromatic foci (SAHF) form in some cell types. Chromatin is inherently dynamic and likely needs to be actively maintained to achieve a stable cell phenotype. In proliferating cells chromatin is maintained in conjunction with DNA replication, but how non-proliferating cells maintain chromatin structure is poorly understood. Some histone variants, such as H3.3 and macroH2A increase as cells undergo senescence, suggesting histone variants and their associated chaperones could be important in chromatin structure maintenance in senescent cells. Here, we discuss options available for senescent cells to maintain chromatin structure and the relative contribution of histone variants and chaperones in this process. This article is part of a Special Issue entitled: Histone chaperones and chromatin assembly.
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Human CABIN1 is a functional member of the human HIRA/UBN1/ASF1a histone H3.3 chaperone complex. Mol Cell Biol 2011; 31:4107-18. [PMID: 21807893 DOI: 10.1128/mcb.05546-11] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mammalian HIRA/UBN1/ASF1a complex is a histone chaperone complex that is conserved from yeast (Saccharomyces cerevisiae) to humans. This complex preferentially deposits the histone variant H3.3 into chromatin in a DNA replication-independent manner and is implicated in diverse chromatin regulatory events from gene activation to heterochromatinization. In yeast, the orthologous complex consists of three Hir proteins (Hir1p, Hir2p, and Hir3p), Hpc2p, and Asf1p. Yeast Hir3p has weak homology to CABIN1, a fourth member of the human complex, suggesting that Hir3p and CABIN1 may be orthologs. Here we show that HIRA and CABIN1 interact at ectopic and endogenous levels of expression in cells, and we isolate the quaternary HIRA/UBN1/CABIN1/ASF1a (HUCA) complex, assembled from recombinant proteins. Mutational analyses support the view that HIRA acts as a scaffold to bring together UBN1, ASF1a, and CABIN1 into a quaternary complex. We show that, like HIRA, UBN1, and ASF1a, CABIN1 is involved in heterochromatinization of the genome of senescent human cells. Moreover, in proliferating cells, HIRA and CABIN1 regulate overlapping sets of genes, and these genes are enriched in the histone variant H3.3. In sum, these data demonstrate that CABIN1 is a functional member of the human HUCA complex and so is the likely ortholog of yeast Hir3p.
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Verdaasdonk JS, Bloom K. Centromeres: unique chromatin structures that drive chromosome segregation. Nat Rev Mol Cell Biol 2011; 12:320-32. [PMID: 21508988 DOI: 10.1038/nrm3107] [Citation(s) in RCA: 166] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Fidelity during chromosome segregation is essential to prevent aneuploidy. The proteins and chromatin at the centromere form a unique site for kinetochore attachment and allow the cell to sense and correct errors during chromosome segregation. Centromeric chromatin is characterized by distinct chromatin organization, epigenetics, centromere-associated proteins and histone variants. These include the histone H3 variant centromeric protein A (CENPA), the composition and deposition of which have been widely investigated. Studies have examined the structural and biophysical properties of the centromere and have suggested that the centromere is not simply a 'landing pad' for kinetochore formation, but has an essential role in mitosis by assembling and directing the organization of the kinetochore.
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Affiliation(s)
- Jolien S Verdaasdonk
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
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Vishnoi N, Flaherty K, Hancock LC, Ferreira ME, Amin AD, Prochasson P. Separation-of-function mutation in HPC2, a member of the HIR complex in S. cerevisiae, results in derepression of the histone genes but does not confer cryptic TATA phenotypes. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2011; 1809:557-66. [PMID: 21782987 DOI: 10.1016/j.bbagrm.2011.07.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2011] [Revised: 07/02/2011] [Accepted: 07/06/2011] [Indexed: 12/29/2022]
Abstract
The HIR complex, which is comprised of the four proteins Hir1, Hir2, Hir3 and Hpc2, was first characterized as a repressor of three of the four histone gene loci in Saccharomyces cerevisiae. Using a bioinformatical approach, previous studies have identified a region of Hpc2 that is conserved in Schizosaccharomyces pombe and humans. Using a similar approach, we identified two additional domains, CDI and CDII, of the Hpc2 protein that are conserved among yeast species related to S. cerevisiae. We showed that the N terminal CDI domain (spanning amino acids 63-79) is dispensable for HIR complex assembly, but plays an essential role in the repression of the histone genes by recruiting the HIR complex to the HIR-dependent histone gene loci. The second conserved domain, CDII (spanning amino acids 452-480), is required for the stability of the Hpc2 protein itself as well as for the assembly of the HIR complex. In addition, we report a novel separation-of-function mutation within CDI of Hpc2, which causes derepression of the histone genes but does not confer other reported hir/hpc- phenotypes (such as Spt phenotypes, heterochromatin silencing defects and repression of cryptic promoters). This is the first direct demonstration that a separation-of-function mutation exists within the HIR complex.
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Affiliation(s)
- Nidhi Vishnoi
- Department of Pathology and Laboratory Medicine, University of Kansas Medical Center, Kansas City, KS 66160, USA
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Li Q, Burgess R, Zhang Z. All roads lead to chromatin: Multiple pathways for histone deposition. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2011; 1819:238-46. [PMID: 21763476 DOI: 10.1016/j.bbagrm.2011.06.013] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2011] [Revised: 06/28/2011] [Accepted: 06/29/2011] [Indexed: 11/28/2022]
Abstract
Chromatin, a complex of DNA and associated proteins, governs diverse processes including gene transcription, DNA replication and DNA repair. The fundamental unit of chromatin is the nucleosome, consisting of 147bp of DNA wound about 1.6 turns around a histone octamer of one (H3-H4)(2) tetramer and two H2A-H2B dimers. In order to form nucleosomes, (H3-H4)(2) tetramers are deposited first, followed by the rapid deposition of H2A-H2B. It is believed that the assembly of (H3-H4)(2) tetramers into nucleosomes is the rate-limiting step of nucleosome assembly. Moreover, assembly of H3-H4 into nucleosomes following DNA replication, DNA repair and gene transcription is likely to be a key step in the inheritance of epigenetic information and maintenance of genome integrity. In this review, we discuss how nucleosome assembly of H3-H4 is regulated by concerted actions of histone chaperones and modifications on newly synthesized H3 and H4. This article is part of a Special Issue entitled: Histone chaperones and Chromatin assembly.
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Genetic interactions between POB3 and the acetylation of newly synthesized histones. Curr Genet 2011; 57:271-86. [PMID: 21656278 DOI: 10.1007/s00294-011-0347-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2011] [Revised: 05/13/2011] [Accepted: 05/14/2011] [Indexed: 10/18/2022]
Abstract
Pob3p is an essential component of the S. cerevisiae FACT complex (yFACT). Several lines of evidence indicate that the yFACT complex plays an important role in chromatin assembly including the observation that the pob3 Q308K allele is synthetically lethal with an allele of histone H4 that prevents the diacetylation of newly synthesized molecules. We have analyzed the genetic interactions between the Q308K allele of POB3 and mutations in all of the sites of acetylation that have been identified on newly synthesized histones. Genetic interactions were observed between POB3 and sites of acetylation on the NH(2)-terminal tails of H3 and H4. For histone H3, lysine residues 14 and 23 were particularly important when POB3 activity is compromised. Surprisingly, synthetic defects observed when the pob3 Q308K allele was combined with mutations of H4 lysines 5 and 12, were not phenocopied by deletion of HAT1, which encodes the enzyme that is thought to generate this pattern of acetylation on H4. Genetic interactions were also observed between POB3 and sites of acetylation found in the core domain of newly synthesized histones H3 and H4. These include synthetic lethality with an allele of H4 lysine 91 that mimics constitutive acetylation. While the mutations that alter H4 lysines 5, 12 and 91 do not affect binding to Pob3p, mutation of histone H3 lysine 56 decreases the association of histones with Pob3p. These results support the model that the yFACT complex plays a central role in chromatin assembly pathways regulated by acetylation of newly synthesized histones.
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Yamane K, Mizuguchi T, Cui B, Zofall M, Noma KI, Grewal SIS. Asf1/HIRA facilitate global histone deacetylation and associate with HP1 to promote nucleosome occupancy at heterochromatic loci. Mol Cell 2011; 41:56-66. [PMID: 21211723 DOI: 10.1016/j.molcel.2010.12.009] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2010] [Revised: 11/03/2010] [Accepted: 11/24/2010] [Indexed: 12/21/2022]
Abstract
Heterochromatin impacts various nuclear processes by providing a recruiting platform for diverse chromosomal proteins. In fission yeast, HP1 proteins Chp2 and Swi6, which bind to methylated histone H3 lysine 9, associate with SHREC (Snf2/HDAC repressor complex) and Clr6 histone deacetylases (HDACs) involved in heterochromatic silencing. However, heterochromatic silencing machinery is not fully defined. We describe a histone chaperone complex containing Asf1 and HIRA that spreads across silenced domains via its association with Swi6 to enforce transcriptional silencing. Asf1 functions in concert with a Clr6 HDAC complex to silence heterochromatic repeats, and it suppresses antisense transcription by promoting histone deacetylation. Furthermore, we demonstrate that Asf1 and SHREC facilitate nucleosome occupancy at heterochromatic regions but TFIIIC transcription factor binding sites within boundary elements are refractory to these factors. These analyses uncover a role for Asf1 in global histone deacetylation and suggest that HP1-associated histone chaperone promotes nucleosome occupancy to assemble repressive heterochromatin.
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Affiliation(s)
- Kenichi Yamane
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, Bethesda, MD 20892, USA
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48
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Jiang WQ, Nguyen A, Cao Y, Chang ACM, Reddel RR. HP1-mediated formation of alternative lengthening of telomeres-associated PML bodies requires HIRA but not ASF1a. PLoS One 2011; 6:e17036. [PMID: 21347226 PMCID: PMC3039646 DOI: 10.1371/journal.pone.0017036] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2010] [Accepted: 01/11/2011] [Indexed: 12/20/2022] Open
Abstract
Approximately 10% of cancers use recombination-mediated Alternative Lengthening of Telomeres (ALT) instead of telomerase to prevent telomere shortening. A characteristic of cells that utilize ALT is the presence of ALT-associated PML nuclear bodies (APBs) containing (TTAGGG)n DNA, telomere binding proteins, DNA recombination proteins, and heterochromatin protein 1 (HP1). The function of APBs is unknown and it is possible that they are functionally heterogeneous. Most ALT cells lack functional p53, and restoration of the p53/p21 pathway in these cells results in growth arrest/senescence and a substantial increase in the number of large APBs that is dependent on two HP1 isoforms, HP1α and HP1γ. Here we investigated the mechanism of HP1-mediated APB formation, and found that histone chaperones, HIRA and ASF1a, are present in APBs following activation of the p53/p21 pathway in ALT cells. HIRA and ASF1a were also found to colocalize inside PML bodies in normal fibroblasts approaching senescence, providing evidence for the existence of a senescence-associated ASF1a/HIRA complex inside PML bodies, consistent with a role for these proteins in induction of senescence in both normal and ALT cells. Moreover, knockdown of HIRA but not ASF1a significantly reduced p53-mediated induction of large APBs, with a concomitant reduction of large HP1 foci. We conclude that HIRA, in addition to its physical and functional association with ASF1a, plays a unique, ASF1a-independent role, which is required for the localization of HP1 to PML bodies and thus for APB formation.
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Affiliation(s)
- Wei-Qin Jiang
- Cancer Research Unit, Children's Medical Research Institute, Westmead, New South Wales, Australia
- Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia
| | - Akira Nguyen
- Cancer Research Unit, Children's Medical Research Institute, Westmead, New South Wales, Australia
- Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia
| | - Ying Cao
- Cancer Research Unit, Children's Medical Research Institute, Westmead, New South Wales, Australia
- Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia
| | - Andy C.-M. Chang
- Cancer Research Unit, Children's Medical Research Institute, Westmead, New South Wales, Australia
- Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia
| | - Roger R. Reddel
- Cancer Research Unit, Children's Medical Research Institute, Westmead, New South Wales, Australia
- Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia
- * E-mail:
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Chang JS, Winston F. Spt10 and Spt21 are required for transcriptional silencing in Saccharomyces cerevisiae. EUKARYOTIC CELL 2011; 10:118-29. [PMID: 21057056 PMCID: PMC3019801 DOI: 10.1128/ec.00246-10] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2010] [Accepted: 10/26/2010] [Indexed: 11/20/2022]
Abstract
In Saccharomyces cerevisiae, transcriptional silencing occurs at three classes of genomic regions: near the telomeres, at the silent mating type loci, and within the ribosomal DNA (rDNA) repeats. In all three cases, silencing depends upon several factors, including specific types of histone modifications. In this work we have investigated the roles in silencing for Spt10 and Spt21, two proteins previously shown to control transcription of particular histone genes. Building on a recent study showing that Spt10 is required for telomeric silencing, our results show that in both spt10 and spt21 mutants, silencing is reduced near telomeres and at HMLα, while it is increased at the rDNA. Both spt10 and spt21 mutations cause modest effects on Sir protein recruitment and histone modifications at telomeric regions, and they cause significant changes in chromatin structure, as judged by its accessibility to dam methylase. These silencing and chromatin changes are not seen upon deletion of HTA2-HTB2, the primary histone locus regulated by Spt10 and Spt21. These results suggest that Spt10 and Spt21 control silencing in S. cerevisiae by altering chromatin structure through roles beyond the control of histone gene expression.
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Affiliation(s)
- Jennifer S. Chang
- Department of Genetics, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, Massachusetts 02115
| | - Fred Winston
- Department of Genetics, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, Massachusetts 02115
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Anderson HE, Kagansky A, Wardle J, Rappsilber J, Allshire RC, Whitehall SK. Silencing mediated by the Schizosaccharomyces pombe HIRA complex is dependent upon the Hpc2-like protein, Hip4. PLoS One 2010; 5:e13488. [PMID: 20976105 PMCID: PMC2956695 DOI: 10.1371/journal.pone.0013488] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Accepted: 09/27/2010] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND HIRA (or Hir) proteins are conserved histone chaperones that function in multi-subunit complexes to mediate replication-independent nucleosome assembly. We have previously demonstrated that the Schizosaccharomyces pombe HIRA proteins, Hip1 and Slm9, form a complex with a TPR repeat protein called Hip3. Here we have identified a new subunit of this complex. METHODOLOGY/PRINCIPAL FINDINGS To identify proteins that interact with the HIRA complex, rapid affinity purifications of Slm9 were performed. Multiple components of the chaperonin containing TCP-1 complex (CCT) and the 19S subunit of the proteasome reproducibly co-purified with Slm9, suggesting that HIRA interacts with these complexes. Slm9 was also found to interact with a previously uncharacterised protein (SPBC947.08c), that we called Hip4. Hip4 contains a HRD domain which is a characteristic of the budding yeast and human HIRA/Hir-binding proteins, Hpc2 and UBN1. Co-precipitation experiments revealed that Hip4 is stably associated with all of the other components of the HIRA complex and deletion of hip4(+) resulted in the characteristic phenotypes of cells lacking HIRA function, such as temperature sensitivity, an elongated cell morphology and hypersensitivity to the spindle poison, thiabendazole. Moreover, loss of Hip4 function alleviated the heterochromatic silencing of reporter genes located in the mating type locus and centromeres and was associated with increased levels of non-coding transcripts derived from centromeric repeat sequences. Hip4 was also found to be required for the distinct form of silencing that controls the expression of Tf2 LTR retrotransposons. CONCLUSIONS/SIGNIFICANCE Overall, these results indicate that Hip4 is an integral component of the HIRA complex that is required for transcriptional silencing at multiple loci.
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Affiliation(s)
- Holly E. Anderson
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle, United Kingdom
| | - Alexander Kagansky
- Wellcome Trust Centre for Cell Biology and Institute of Cell Biology, University of Edinburgh, Edinburgh, Scotland, United Kingdom
| | - Josephine Wardle
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle, United Kingdom
| | - Juri Rappsilber
- Wellcome Trust Centre for Cell Biology and Institute of Cell Biology, University of Edinburgh, Edinburgh, Scotland, United Kingdom
| | - Robin C. Allshire
- Wellcome Trust Centre for Cell Biology and Institute of Cell Biology, University of Edinburgh, Edinburgh, Scotland, United Kingdom
| | - Simon K. Whitehall
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle, United Kingdom
- * E-mail:
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