title: Checkpoint-Independent Regulation of Origin Firing by Mrc1 through Interaction with Hsk1 Kinase.
abstract: Mrc1 is a conserved checkpoint mediator protein that transduces the replication stress signal to the downstream effector kinase. The loss ofmrc1checkpoint activity results in the aberrant activation of late/dormant origins in the presence of hydroxyurea. Mrc1 was also suggested to regulate orders of early origin firing in a checkpoint-independent manner, but its mechanism was unknown. Here we identify HBS (Hsk1 bypass segment) on Mrc1. An ΔHBSmutant does not activate late/dormant origin firing in the presence of hydroxyurea but causes the precocious and enhanced activation of weak early-firing origins during normal S-phase progression and bypasses the requirement for Hsk1 for growth. This may be caused by the disruption of intramolecular binding between HBS and NTHBS (N-terminal target of HBS). Hsk1 binds to Mrc1 through HBS and phosphorylates a segment adjacent to NTHBS, disrupting the intramolecular interaction. We propose that Mrc1 exerts a "brake" on initiation (through intramolecular interactions) and that this brake can be released (upon the loss of intramolecular interactions) by either the Hsk1-mediated phosphorylation of Mrc1 or the deletion of HBS (or a phosphomimic mutation of putative Hsk1 target serine/threonine), which can bypass the function of Hsk1 for growth. The brake mechanism may explain the checkpoint-independent regulation of early origin firing in fission yeast.
authors.affiliation: Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Matsumoto
authors.affiliation: Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Kanoh
authors.affiliation: Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Michie
authors.initials: M
authors.lastname: Shimmoto
authors.affiliation: Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Motoshi
authors.initials: M
authors.lastname: Hayano
authors.affiliation: Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Kyosuke
authors.initials: K
authors.lastname: Ueda
authors.affiliation: Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Rino
authors.initials: R
authors.lastname: Fukatsu
authors.affiliation: Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Naoko
authors.initials: N
authors.lastname: Kakusho
authors.affiliation: Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan masai-hs@igakuken.or.jp.
authors.forename: Hisao
authors.initials: H
authors.lastname: Masai
mesh_terms: D000595:Amino Acid Sequence; D059447:Cell Cycle Checkpoints / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006918:Hydroxyurea / Q000494:pharmacology; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D010455:Peptides / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D018741:Replication Origin / Q000187:drug effects; D012568:Schizosaccharomyces / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C533276:MRC1 protein, S pombe; D010455:Peptides; D029702:Schizosaccharomyces pombe Proteins; C094761:HSK1 protein, S pombe; D017346:Protein Serine-Threonine Kinases; D006918:Hydroxyurea
keywords: DNA replication timing; Hsk1; Mrc1; intramolecular interaction; replication checkpoint