Abstract
Genome stability depends on faithful chromosome segregation, which relies on maintenance of chromatid cohesion during S phase. In eukaryotes, Pds1/securin is the only known inhibitor that can prevent loss of cohesion. However, pds1Δ yeast cells and securin-null mice are viable. We sought to identify redundant mechanisms that promote cohesion within S phase in the absence of Pds1 and found that cells lacking the S-phase cyclins Clb5 and Clb6 have a cohesion defect under conditions of replication stress. Similar to the phenotype of pds1Δ cells, loss of cohesion in cells lacking Clb5 and Clb6 is dependent on Esp1. However, Pds1 phosphorylation by Cdk-cyclin is not required for cohesion. Moreover, cells lacking Clb5, Clb6, and Pds1 are inviable and lose cohesion during an unperturbed S phase, indicating that Pds1 and specific B-type cyclins promote cohesion independently of one another. Consistent with this, we find that Mcd1/Scc1 is less abundant on chromosomes in cells lacking Clb5 and Clb6 during replication stress. However, clb5Δ clb6Δ cells do accumulate Mcd1/Scc1 at centromeres upon mitotic arrest, suggesting that the cyclin-dependent mechanism is S phase specific. These data indicate that Clb5 and Clb6 promote cohesion which is then protected by Pds1 and that both mechanisms are required during replication stress.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, U.S. Gov't, Non-P.H.S.
MeSH terms
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Animals
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CDC28 Protein Kinase, S cerevisiae / genetics
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CDC28 Protein Kinase, S cerevisiae / metabolism
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Cell Cycle Proteins / genetics
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Cell Cycle Proteins / metabolism*
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Chromatids / metabolism*
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Chromosome Segregation
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Cyclin B / genetics
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Cyclin B / metabolism*
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Cyclin-Dependent Kinases / genetics
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Cyclin-Dependent Kinases / metabolism*
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DNA Replication
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism
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Endopeptidases / genetics
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Endopeptidases / metabolism
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Gene Knockdown Techniques
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Humans
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Hydroxyurea / pharmacology
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Mice
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Minichromosome Maintenance Complex Component 7
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Nuclear Proteins / genetics
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Nuclear Proteins / metabolism*
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Nucleic Acid Synthesis Inhibitors / pharmacology
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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S Phase / physiology*
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Saccharomyces cerevisiae / cytology
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Saccharomyces cerevisiae / drug effects
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Saccharomyces cerevisiae / physiology*
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Saccharomyces cerevisiae Proteins / genetics
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Saccharomyces cerevisiae Proteins / metabolism*
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Securin
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Separase
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Spindle Apparatus / metabolism
Substances
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CLB5 protein, S cerevisiae
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CLB6 protein, S cerevisiae
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Cell Cycle Proteins
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Cyclin B
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DNA-Binding Proteins
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Nuclear Proteins
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Nucleic Acid Synthesis Inhibitors
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PDS1 protein, S cerevisiae
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Recombinant Fusion Proteins
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Saccharomyces cerevisiae Proteins
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Securin
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CDC28 Protein Kinase, S cerevisiae
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Cyclin-Dependent Kinases
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Endopeptidases
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ESP1 protein, S cerevisiae
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Separase
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MCM7 protein, S cerevisiae
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Minichromosome Maintenance Complex Component 7
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Hydroxyurea