title: The Hsk1(Cdc7) replication kinase regulates origin efficiency.
abstract: Origins of DNA replication are generally inefficient, with most firing in fewer than half of cell cycles. However, neither the mechanism nor the importance of the regulation of origin efficiency is clear. In fission yeast, origin firing is stochastic, leading us to hypothesize that origin inefficiency and stochasticity are the result of a diffusible, rate-limiting activator. We show that the Hsk1-Dfp1 replication kinase (the fission yeast Cdc7-Dbf4 homologue) plays such a role. Increasing or decreasing Hsk1-Dfp1 levels correspondingly increases or decreases origin efficiency. Furthermore, tethering Hsk1-Dfp1 near an origin increases the efficiency of that origin, suggesting that the effective local concentration of Hsk1-Dfp1 regulates origin firing. Using photobleaching, we show that Hsk1-Dfp1 is freely diffusible in the nucleus. These results support a model in which the accessibility of replication origins to Hsk1-Dfp1 regulates origin efficiency and provides a potential mechanistic link between chromatin structure and replication timing. By manipulating Hsk1-Dfp1 levels, we show that increasing or decreasing origin firing rates leads to an increase in genomic instability, demonstrating the biological importance of appropriate origin efficiency.
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
authors.forename: Prasanta K
authors.initials: PK
authors.lastname: Patel
authors.forename: Naveen
authors.initials: N
authors.lastname: Kommajosyula
authors.forename: Adam
authors.initials: A
authors.lastname: Rosebrock
authors.forename: Aaron
authors.initials: A
authors.lastname: Bensimon
authors.forename: Janet
authors.initials: J
authors.lastname: Leatherwood
authors.forename: John
authors.initials: J
authors.lastname: Bechhoefer
authors.forename: Nicholas
authors.initials: N
authors.lastname: Rhind
mesh_terms: D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D043171:Chromosomal Instability; D004261:DNA Replication; D036681:Fluorescence Recovery After Photobleaching; D015966:Gene Expression Regulation, Fungal; D010957:Plasmids / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D018741:Replication Origin; D012568:Schizosaccharomyces / Q000166:cytology / Q000502:physiology; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D029702:Schizosaccharomyces pombe Proteins; D011494:Protein Kinases; C507988:Dfp1 protein, S pombe; C094761:HSK1 protein, S pombe; D017346:Protein Serine-Threonine Kinases
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