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Constantinou M, Charidemou E, Shanlitourk I, Strati K, Kirmizis A. Yeast Nat4 regulates DNA damage checkpoint signaling through its N-terminal acetyltransferase activity on histone H4. PLoS Genet 2024; 20:e1011433. [PMID: 39356727 PMCID: PMC11472955 DOI: 10.1371/journal.pgen.1011433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2024] [Revised: 10/14/2024] [Accepted: 09/20/2024] [Indexed: 10/04/2024] Open
Abstract
The DNA damage response (DDR) constitutes a vital cellular process that safeguards genome integrity. This biological process involves substantial alterations in chromatin structure, commonly orchestrated by epigenetic enzymes. Here, we show that the epigenetic modifier N-terminal acetyltransferase 4 (Nat4), known to acetylate the alpha-amino group of serine 1 on histones H4 and H2A, is implicated in the response to DNA damage in S. cerevisiae. Initially, we demonstrate that yeast cells lacking Nat4 have an increased sensitivity to DNA damage and accumulate more DNA breaks than wild-type cells. Accordingly, upon DNA damage, NAT4 gene expression is elevated, and the enzyme is specifically recruited at double-strand breaks. Delving deeper into its effects on the DNA damage signaling cascade, nat4-deleted cells exhibit lower levels of the damage-induced modification H2AS129ph (γH2A), accompanied by diminished binding of the checkpoint control protein Rad9 surrounding the double-strand break. Consistently, Mec1 kinase recruitment at double-strand breaks, critical for H2AS129ph deposition and Rad9 retention, is significantly impaired in nat4Δ cells. Consequently, Mec1-dependent phosphorylation of downstream effector kinase Rad53, indicative of DNA damage checkpoint activation, is reduced. Importantly, we found that the effects of Nat4 in regulating the checkpoint signaling cascade are mediated by its N-terminal acetyltransferase activity targeted specifically towards histone H4. Overall, this study points towards a novel functional link between histone N-terminal acetyltransferase Nat4 and the DDR, associating a new histone-modifying activity in the maintenance of genome integrity.
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Affiliation(s)
| | - Evelina Charidemou
- Department of Biological Sciences, University of Cyprus, Nicosia, Cyprus
| | - Izge Shanlitourk
- Department of Biological Sciences, University of Cyprus, Nicosia, Cyprus
| | - Katerina Strati
- Department of Biological Sciences, University of Cyprus, Nicosia, Cyprus
| | - Antonis Kirmizis
- Department of Biological Sciences, University of Cyprus, Nicosia, Cyprus
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2
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Reinhardt R, Leonard TA. A critical evaluation of protein kinase regulation by activation loop autophosphorylation. eLife 2023; 12:e88210. [PMID: 37470698 PMCID: PMC10359097 DOI: 10.7554/elife.88210] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 07/07/2023] [Indexed: 07/21/2023] Open
Abstract
Phosphorylation of proteins is a ubiquitous mechanism of regulating their function, localization, or activity. Protein kinases, enzymes that use ATP to phosphorylate protein substrates are, therefore, powerful signal transducers in eukaryotic cells. The mechanism of phosphoryl-transfer is universally conserved among protein kinases, which necessitates the tight regulation of kinase activity for the orchestration of cellular processes with high spatial and temporal fidelity. In response to a stimulus, many kinases enhance their own activity by autophosphorylating a conserved amino acid in their activation loop, but precisely how this reaction is performed is controversial. Classically, kinases that autophosphorylate their activation loop are thought to perform the reaction in trans, mediated by transient dimerization of their kinase domains. However, motivated by the recently discovered regulation mechanism of activation loop cis-autophosphorylation by a kinase that is autoinhibited in trans, we here review the various mechanisms of autoregulation that have been proposed. We provide a framework for critically evaluating biochemical, kinetic, and structural evidence for protein kinase dimerization and autophosphorylation, and share some thoughts on the implications of these mechanisms within physiological signaling networks.
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Affiliation(s)
- Ronja Reinhardt
- Max Perutz Labs, Vienna Biocenter Campus (VBC)ViennaAustria
- Medical University of Vienna, Center for Medical BiochemistryViennaAustria
| | - Thomas A Leonard
- Max Perutz Labs, Vienna Biocenter Campus (VBC)ViennaAustria
- Medical University of Vienna, Center for Medical BiochemistryViennaAustria
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3
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Stolarova L, Kleiblova P, Janatova M, Soukupova J, Zemankova P, Macurek L, Kleibl Z. CHEK2 Germline Variants in Cancer Predisposition: Stalemate Rather than Checkmate. Cells 2020; 9:cells9122675. [PMID: 33322746 PMCID: PMC7763663 DOI: 10.3390/cells9122675] [Citation(s) in RCA: 100] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2020] [Revised: 12/04/2020] [Accepted: 12/10/2020] [Indexed: 12/15/2022] Open
Abstract
Germline alterations in many genes coding for proteins regulating DNA repair and DNA damage response (DDR) to DNA double-strand breaks (DDSB) have been recognized as pathogenic factors in hereditary cancer predisposition. The ATM-CHEK2-p53 axis has been documented as a backbone for DDR and hypothesized as a barrier against cancer initiation. However, although CHK2 kinase coded by the CHEK2 gene expedites the DDR signal, its function in activation of p53-dependent cell cycle arrest is dispensable. CHEK2 mutations rank among the most frequent germline alterations revealed by germline genetic testing for various hereditary cancer predispositions, but their interpretation is not trivial. From the perspective of interpretation of germline CHEK2 variants, we review the current knowledge related to the structure of the CHEK2 gene, the function of CHK2 kinase, and the clinical significance of CHEK2 germline mutations in patients with hereditary breast, prostate, kidney, thyroid, and colon cancers.
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Affiliation(s)
- Lenka Stolarova
- Institute of Biochemistry and Experimental Oncology, First Faculty of Medicine, Charles University, 12800 Prague, Czech Republic; (L.S.); (M.J.); (J.S.); (P.Z.)
- Laboratory of Cancer Cell Biology, Institute of Molecular Genetics of the Czech Academy of Sciences, 14220 Prague, Czech Republic;
| | - Petra Kleiblova
- Institute of Biology and Medical Genetics, First Faculty of Medicine, Charles University and General University Hospital in Prague, 12800 Prague, Czech Republic;
| | - Marketa Janatova
- Institute of Biochemistry and Experimental Oncology, First Faculty of Medicine, Charles University, 12800 Prague, Czech Republic; (L.S.); (M.J.); (J.S.); (P.Z.)
| | - Jana Soukupova
- Institute of Biochemistry and Experimental Oncology, First Faculty of Medicine, Charles University, 12800 Prague, Czech Republic; (L.S.); (M.J.); (J.S.); (P.Z.)
| | - Petra Zemankova
- Institute of Biochemistry and Experimental Oncology, First Faculty of Medicine, Charles University, 12800 Prague, Czech Republic; (L.S.); (M.J.); (J.S.); (P.Z.)
| | - Libor Macurek
- Laboratory of Cancer Cell Biology, Institute of Molecular Genetics of the Czech Academy of Sciences, 14220 Prague, Czech Republic;
| | - Zdenek Kleibl
- Institute of Biochemistry and Experimental Oncology, First Faculty of Medicine, Charles University, 12800 Prague, Czech Republic; (L.S.); (M.J.); (J.S.); (P.Z.)
- Correspondence: ; Tel.: +420-22496-745
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Abd Wahab S, Remus D. Antagonistic control of DDK binding to licensed replication origins by Mcm2 and Rad53. eLife 2020; 9:58571. [PMID: 32701054 PMCID: PMC7398698 DOI: 10.7554/elife.58571] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Accepted: 07/22/2020] [Indexed: 12/12/2022] Open
Abstract
Eukaryotic replication origins are licensed by the loading of the replicative DNA helicase, Mcm2-7, in inactive double hexameric form around DNA. Subsequent origin activation is under control of multiple protein kinases that either promote or inhibit origin activation, which is important for genome maintenance. Using the reconstituted budding yeast DNA replication system, we find that the flexible N-terminal extension (NTE) of Mcm2 promotes the stable recruitment of Dbf4-dependent kinase (DDK) to Mcm2-7 double hexamers, which in turn promotes DDK phosphorylation of Mcm4 and −6 and subsequent origin activation. Conversely, we demonstrate that the checkpoint kinase, Rad53, inhibits DDK binding to Mcm2-7 double hexamers. Unexpectedly, this function is not dependent on Rad53 kinase activity, suggesting steric inhibition of DDK by activated Rad53. These findings identify critical determinants of the origin activation reaction and uncover a novel mechanism for checkpoint-dependent origin inhibition.
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Affiliation(s)
- Syafiq Abd Wahab
- Molecular Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, United States.,Weill-Cornell Graduate School of Medical Sciences, New York, United States
| | - Dirk Remus
- Molecular Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, United States.,Weill-Cornell Graduate School of Medical Sciences, New York, United States
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5
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Wahab SA, Remus D. Antagonistic control of DDK binding to licensed replication origins by Mcm2 and Rad53.. [DOI: 10.1101/2020.05.04.077628] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
Abstract
ABSTRACTEukaryotic replication origins are licensed by the loading of the replicative DNA helicase, Mcm2-7, in inactive double hexameric form around DNA. Subsequent origin activation is under control of multiple protein kinases that either promote or inhibit origin activation, which is important for genome maintenance. Using the reconstituted budding yeast DNA replication system, we find that the flexible N-terminal tail of Mcm2 promotes the stable recruitment of Dbf4-dependent kinase (DDK) to Mcm2-7 double hexamers, which in turn promotes DDK phosphorylation of Mcm4 and -6 and subsequent origin activation. Conversely, we demonstrate that the checkpoint kinase, Rad53, inhibits DDK binding to Mcm2-7 double hexamers. Unexpectedly, this function is not dependent on Rad53 kinase activity, but requires Rad53 activation by trans-autophosphorylation, suggesting steric inhibition of DDK by activated Rad53. These findings identify critical determinants of the origin activation reaction and uncover a novel mechanism for checkpoint-dependent origin inhibition.
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Reinhardt R, Truebestein L, Schmidt HA, Leonard TA. It Takes Two to Tango: Activation of Protein Kinase D by Dimerization. Bioessays 2020; 42:e1900222. [PMID: 31997382 DOI: 10.1002/bies.201900222] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 01/10/2020] [Indexed: 12/23/2022]
Abstract
The recent discovery and structure determination of a novel ubiquitin-like dimerization domain in protein kinase D (PKD) has significant implications for its activation. PKD is a serine/threonine kinase activated by the lipid second messenger diacylglycerol (DAG). It is an essential and highly conserved protein that is implicated in plasma membrane directed trafficking processes from the trans-Golgi network. However, many open questions surround its mechanism of activation, its localization, and its role in the biogenesis of cargo transport carriers. In reviewing this field, the focus is primarily on the mechanisms that control the activation of PKD at precise locations in the cell. In light of the new structural findings, the understanding of the mechanisms underlying PKD activation is critically evaluated, with particular emphasis on the role of dimerization in PKD autophosphorylation, and the provenance and recognition of the DAG that activates PKD.
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Affiliation(s)
- Ronja Reinhardt
- Department of Structural and Computational Biology, Max Perutz Labs, Vienna Biocenter, 1030, Vienna, Austria.,Department of Medical Biochemistry, Medical University of Vienna, 1030, Vienna, Austria
| | - Linda Truebestein
- Department of Structural and Computational Biology, Max Perutz Labs, Vienna Biocenter, 1030, Vienna, Austria.,Department of Medical Biochemistry, Medical University of Vienna, 1030, Vienna, Austria
| | - Heiko A Schmidt
- Center for Integrative Bioinformatics Vienna, Max Perutz Labs, University of Vienna and Medical University of Vienna, Vienna Biocenter, 1030, Vienna, Austria
| | - Thomas A Leonard
- Department of Structural and Computational Biology, Max Perutz Labs, Vienna Biocenter, 1030, Vienna, Austria.,Department of Medical Biochemistry, Medical University of Vienna, 1030, Vienna, Austria
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7
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Ahiri A, Garmes H, Podlipnik C, Aboulmouhajir A. Insights into evolutionary interaction patterns of the 'Phosphorylation Activation Segment' in kinase. Bioinformation 2019; 15:666-677. [PMID: 31787816 PMCID: PMC6859708 DOI: 10.6026/97320630015666] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2019] [Revised: 10/07/2019] [Accepted: 10/09/2019] [Indexed: 12/17/2022] Open
Abstract
We are interested in studying the phosphorylation of the kinase activation loop, distinguishing the passage from the unphosphorylated to the phosphorylated form without allostery. We performed an interaction study to trace the change of interactions between the activation segment and the kinase catalytic core, before and after phosphorylation. Results show that the structural changes are mainly due to the attraction between the phosphate group and guanidine groups of the arginine side chains of RD-pocket, which are constituted mainly of guanidine groups of the catalytic loop, the β9, and the αC helix. This attraction causes propagation of structural variation of the activation segment, principally towards the N-terminal. The structural variations are not made on all the amino acids of the activation segment; they are conditioned by the existence of two beta sheets stabilizing the loop during phosphorylation. The first,β6-β9 sheet is usually present in most of the kinases; the second, β10-β11 is formed due to the interaction between the main chain amino acids of the activation loop and the αEF/αF loop.
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Affiliation(s)
- Adil Ahiri
- Modeling and Molecular Spectroscopy Team, Faculty of Sciences, University Chouaib Doukkali, El-Jadida, Morroco
| | - Hocine Garmes
- Analytical Chemistry and Environmental Sciences Team, Department of chemistry, Faculty of Science, University Chouaib Doukkali, El Jadida, Morroco
| | - Crtomir Podlipnik
- Faculty of Chemistry and Chemical Technology, University of Ljubljana, Ljubljana, Slovenia
| | - Aziz Aboulmouhajir
- Modeling and Molecular Spectroscopy Team, Faculty of Sciences, University Chouaib Doukkali, El-Jadida, Morroco
- Extraction, Spectroscopy and Valorization Team, Organic synthesis, Extraction and Valorization Laboratory, Faculty of Sciences of Ain Chock, Hassan II University, Casablanca, Morocco
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Chen ESW, Weng JH, Chen YH, Wang SC, Liu XX, Huang WC, Matsui T, Kawano Y, Liao JH, Lim LH, Bessho Y, Huang KF, Wu WJ, Tsai MD. Phospho-Priming Confers Functionally Relevant Specificities for Rad53 Kinase Autophosphorylation. Biochemistry 2017; 56:5112-5124. [PMID: 28858528 DOI: 10.1021/acs.biochem.7b00689] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The vast majority of in vitro structural and functional studies of the activation mechanism of protein kinases use the kinase domain alone. Well-demonstrated effects of regulatory domains or allosteric factors are scarce for serine/threonine kinases. Here we use a site-specifically phosphorylated SCD1-FHA1-kinase three-domain construct of the serine/threonine kinase Rad53 to show the effect of phospho-priming, an in vivo regulatory mechanism, on the autophosphorylation intermediate and specificity. Unphosphorylated Rad53 is a flexible monomer in solution but is captured in an asymmetric enzyme:substrate complex in crystal with the two FHA domains separated from each other. Phospho-priming induces formation of a stable dimer via intermolecular pT-FHA binding in solution. Importantly, autophosphorylation of unprimed and phospho-primed Rad53 produced predominantly inactive pS350-Rad53 and active pT354-Rad53, respectively. The latter mechanism was also demonstrated in vivo. Our results show that, while Rad53 can display active conformations under various conditions, simulation of in vivo regulatory conditions confers functionally relevant autophosphorylation.
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Affiliation(s)
- Eric Sheng-Wen Chen
- Institute of Biological Chemistry, Academia Sinica , Taipei 115, Taiwan.,Institute of Biochemical Sciences, National Taiwan University , Taipei 106, Taiwan
| | - Jui-Hung Weng
- Institute of Biological Chemistry, Academia Sinica , Taipei 115, Taiwan.,Institute of Biochemical Sciences, Department of Chemistry, National Tsing Hua University , Hsinchu 300, Taiwan
| | - Yu-Hou Chen
- Institute of Biological Chemistry, Academia Sinica , Taipei 115, Taiwan
| | - Shun-Chang Wang
- Institute of Biological Chemistry, Academia Sinica , Taipei 115, Taiwan
| | - Xiao-Xia Liu
- Institute of Biological Chemistry, Academia Sinica , Taipei 115, Taiwan
| | - Wei-Cheng Huang
- Institute of Biological Chemistry, Academia Sinica , Taipei 115, Taiwan
| | - Tsutomu Matsui
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University , Menlo Park, California 94025, United States
| | - Yoshiaki Kawano
- RIKEN SPring-8 Center , 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan
| | - Jiahn-Haur Liao
- Institute of Biological Chemistry, Academia Sinica , Taipei 115, Taiwan
| | - Liang-Hin Lim
- Institute of Biological Chemistry, Academia Sinica , Taipei 115, Taiwan.,Institute of Biochemical Sciences, National Taiwan University , Taipei 106, Taiwan
| | - Yoshitaka Bessho
- Institute of Biological Chemistry, Academia Sinica , Taipei 115, Taiwan
| | - Kai-Fa Huang
- Institute of Biological Chemistry, Academia Sinica , Taipei 115, Taiwan
| | - Wen-Jin Wu
- Institute of Biological Chemistry, Academia Sinica , Taipei 115, Taiwan
| | - Ming-Daw Tsai
- Institute of Biological Chemistry, Academia Sinica , Taipei 115, Taiwan.,Institute of Biochemical Sciences, National Taiwan University , Taipei 106, Taiwan
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Almawi AW, Matthews LA, Guarné A. FHA domains: Phosphopeptide binding and beyond. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2017; 127:105-110. [DOI: 10.1016/j.pbiomolbio.2016.12.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2016] [Accepted: 12/06/2016] [Indexed: 01/18/2023]
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10
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Beenstock J, Mooshayef N, Engelberg D. How Do Protein Kinases Take a Selfie (Autophosphorylate)? Trends Biochem Sci 2016; 41:938-953. [DOI: 10.1016/j.tibs.2016.08.006] [Citation(s) in RCA: 81] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2016] [Revised: 07/13/2016] [Accepted: 08/02/2016] [Indexed: 12/18/2022]
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11
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Almawi AW, Matthews LA, Larasati, Myrox P, Boulton S, Lai C, Moraes T, Melacini G, Ghirlando R, Duncker BP, Guarné A. 'AND' logic gates at work: Crystal structure of Rad53 bound to Dbf4 and Cdc7. Sci Rep 2016; 6:34237. [PMID: 27681475 PMCID: PMC5041073 DOI: 10.1038/srep34237] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 09/07/2016] [Indexed: 01/07/2023] Open
Abstract
Forkhead-associated (FHA) domains are phosphopeptide recognition modules found in many signaling proteins. The Saccharomyces cerevisiae protein kinase Rad53 is a key regulator of the DNA damage checkpoint and uses its two FHA domains to interact with multiple binding partners during the checkpoint response. One of these binding partners is the Dbf4-dependent kinase (DDK), a heterodimer composed of the Cdc7 kinase and its regulatory subunit Dbf4. Binding of Rad53 to DDK, through its N-terminal FHA (FHA1) domain, ultimately inhibits DDK kinase activity, thereby preventing firing of late origins. We have previously found that the FHA1 domain of Rad53 binds simultaneously to Dbf4 and a phosphoepitope, suggesting that this domain functions as an 'AND' logic gate. Here, we present the crystal structures of the FHA1 domain of Rad53 bound to Dbf4, in the presence and absence of a Cdc7 phosphorylated peptide. Our results reveal how the FHA1 uses a canonical binding interface to recognize the Cdc7 phosphopeptide and a non-canonical interface to bind Dbf4. Based on these data we propose a mechanism to explain how Rad53 enhances the specificity of FHA1-mediated transient interactions.
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Affiliation(s)
- Ahmad W. Almawi
- Department of Biochemistry and Biomedical Sciences, ON, Canada
| | | | - Larasati
- Department of Biology, University of Waterloo, Waterloo, ON, Canada
| | - Polina Myrox
- Department of Biology, University of Waterloo, Waterloo, ON, Canada
| | - Stephen Boulton
- Department of Chemistry and Chemical Biology, McMaster University, ON, Canada
| | - Christine Lai
- Department of Biochemistry, University of Toronto, Toronto, Canada
| | - Trevor Moraes
- Department of Biochemistry, University of Toronto, Toronto, Canada
| | - Giuseppe Melacini
- Department of Chemistry and Chemical Biology, McMaster University, ON, Canada
| | - Rodolfo Ghirlando
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
| | | | - Alba Guarné
- Department of Biochemistry and Biomedical Sciences, ON, Canada,
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12
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DNA damage signalling targets the kinetochore to promote chromatin mobility. Nat Cell Biol 2016; 18:281-90. [PMID: 26829389 DOI: 10.1038/ncb3308] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 01/04/2016] [Indexed: 12/11/2022]
Abstract
In budding yeast, chromatin mobility increases after a DNA double-strand break (DSB). This increase is dependent on Mec1, the yeast ATR kinase, but the targets responsible for this phenomenon are unknown. Here we report that the Mec1-dependent phosphorylation of Cep3, a kinetochore component, is required to stimulate chromatin mobility after DNA breaks. Cep3 phosphorylation counteracts a constraint on chromosome movement imposed by the attachment of centromeres to the spindle pole body. A second constraint, imposed by the tethering of telomeres to the nuclear periphery, is also relieved after chromosome breakage. A non-phosphorylatable Cep3 mutant that impairs DSB-induced chromatin mobility is proficient in DSB repair, suggesting that break-induced chromatin mobility may be dispensable for homology search. Rather, we propose that the relief of centromeric constraint promotes cell cycle arrest and faithful chromosome segregation through the engagement of the spindle assembly checkpoint.
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