Multiple pathways can bypass the essential role of fission yeast Hsk1 kinase in DNA replication initiation.
Cdc7/Hsk1 is a conserved kinase required for initiation of DNA replication that potentially regulates timing and locations of replication origin firing. Here, we show that viability of fission yeast hsk1Δ cells can be restored by loss of mrc1, which is required for maintenance of replication fork integrity, by cds1Δ, or by a checkpoint-deficient mutant of mrc1. In these mutants, normally inactive origins are activated in the presence of hydroxyurea and binding of Cdc45 to MCM is stimulated. mrc1Δ bypasses hsk1Δ more efficiently because of its checkpoint-independent inhibitory functions. Unexpectedly, hsk1Δ is viable at 37°C. More DNA is synthesized, and some dormant origins fire in the presence of hydroxyurea at 37°C. Furthermore, hsk1Δ bypass strains grow poorly at 25°C compared with higher temperatures. Our results show that Hsk1 functions for DNA replication can be bypassed by different genetic backgrounds as well as under varied physiological conditions, providing additional evidence for plasticity of the replication program in eukaryotes.
Genome Dynamics Project, Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, Setagaya-ku, Tokyo 156-8613, Japan.
Seiji
S
Matsumoto
Motoshi
M
Hayano
Yutaka
Y
Kanoh
Hisao
H
Masai
D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication; D004271:DNA, Fungal / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / 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 / Q000201:enzymology* / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics*; D013696:Temperature
C116395:CDC45 protein, S pombe; D018797:Cell Cycle Proteins; D004271:DNA, Fungal; D004268:DNA-Binding Proteins; C533276:MRC1 protein, S pombe; D009687:Nuclear Proteins; D029702:Schizosaccharomyces pombe Proteins; D011494:Protein Kinases; C507988:Dfp1 protein, S pombe; C094761:HSK1 protein, S pombe; D017346:Protein Serine-Threonine Kinases