Regulation of initiation of S phase, replication checkpoint signaling, andmaintenance of mitotic chromosome structures during S phase by Hsk1 kinasein the fission yeast

Takeda, T Ogino, K Tatebayashi, K Ikeda, H Arai, K Masai, H

T. Takeda et al., Regulation of initiation of S phase, replication checkpoint signaling, andmaintenance of mitotic chromosome structures during S phase by Hsk1 kinasein the fission yeast, MOL BIOL CE, 12(5), 2001, pp. 1257-1274

75

INGLESE

Article

Cell & Developmental Biology

MOLECULAR BIOLOGY OF THE CELL

1059-1524 → ACNP

12

5

2001

1257 - 1274

ISI

1059-1524(200105)12:5<1257:ROIOSP>2.0.ZU;2-N

Hsk1, Saccharomyces cerevisiae Cdc7-related kinase in Shizosaccharomyces po mbe, is required for G1/S transition and its kinase activity is controlled by the regulatory subunit Dfp1/Him1. Analyses of a newly isolated temperatu re-sensitive mutant, hsk1-89, reveal that Hsk1 plays crucial roles in DNA r eplication checkpoint signaling and maintenance of proper chromatin structu res during mitotic S phase through regulating the functions of Rad3 (ATM)-C ds1 and Rad21 (cohesin), respectively, in addition to expected essential ro les for initiation of mitotic DNA replication through phosphorylating Cdc19 (Mcm2). Checkpoint defect in hsk1-89 is indicated by accumulation of cut c ells at 30 degreesC. hsk1-89 displays synthetic lethality in combination wi th rad3 deletion, indicating that survival of hsk1-89 depends on Rad3-depen dent checkpoint pathway. Cds1 kinase activation, which normally occurs in r esponse to early S phase arrest by nucleotide deprivation, is largely impai red in hsk1-89. Furthermore, Cds1-dependent hyperphosphorylation of Dfp1 in response to hydroxyurea arrest is eliminated in hsk1-89, suggesting that s ufficient activation of Hsk1-Dfp1 kinase is required for S phase entry and replication checkpoint signaling. hsk1-89 displays apparent defect in mitos is at 37 degreesC leading to accumulation of cells with near 2C DNA content and with aberrant nuclear structures. These phenotypes are similar to thos e of rad21-K1 and are significantly enhanced in a hsk1-89 rad21-K1 double m utant. Consistent with essential roles of Rad21 as a component for the cohe sin complex, sister chromatid cohesion is partially impaired in hsk1-89, su ggesting a possibility that infrequent origin firing of the mutant may affe ct the cohesin functions during S phase.