Hsk1 kinase and Cdc45 regulate replication stress-induced checkpoint responses in fission yeast

Cell Cycle. 2010 Dec 1;9(23):4627-37. doi: 10.4161/cc.9.23.13937. Epub 2010 Dec 1.


In fission yeast, replication fork arrest activates the replication checkpoint effector kinase Cds1(Chk2/Rad53) through the Rad3(ATR/Mec1)-Mrc1(Claspin) pathway. Hsk1, the Cdc7 homologue of fission yeast required for efficient initiation of DNA replication, is also required for Cds1 activation. Hsk1 kinase activity is required for induction and maintenance of Mrc1 hyperphosphorylation, which is induced by replication fork block and mediated by Rad3. Rad3 kinase activity does not change in an hsk1 temperature-sensitive mutant, and Hsk1 kinase activity is not affected by rad3 mutation. Hsk1 kinase vigorously phosphorylates Mrc1 in vitro, predominantly at non-SQ/TQ sites, but this phosphorylation does not seem to affect the Rad3 action on Mrc1. Interestingly, the replication stress-induced activation of Cds1 and hyperphosphorylation of Mrc1 is almost completely abrogated in an initiation-defective mutant of cdc45, but not in an mcm2 or polε mutant. The results suggest that Hsk1-mediated loading of Cdc45 onto replication origins may play important roles in replication stress-induced checkpoint.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Checkpoint Kinase 2
  • DNA Replication
  • DNA-Binding Proteins / metabolism*
  • Nuclear Proteins / metabolism*
  • Phosphorylation
  • Protein Kinases / metabolism
  • Protein-Serine-Threonine Kinases / metabolism*
  • Replication Origin
  • Schizosaccharomyces / enzymology
  • Schizosaccharomyces / metabolism*
  • Schizosaccharomyces pombe Proteins / genetics
  • Schizosaccharomyces pombe Proteins / metabolism*
  • Stress, Physiological


  • CDC45 protein, S pombe
  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • MRC1 protein, S pombe
  • Nuclear Proteins
  • Schizosaccharomyces pombe Proteins
  • Protein Kinases
  • Checkpoint Kinase 2
  • Cds1 protein, S pombe
  • HSK1 protein, S pombe
  • Protein-Serine-Threonine Kinases
  • rad3 protein, S pombe
  • mcm2 protein, S pombe