Cig2, a B-type cyclin, promotes the onset of S in Schizosaccharomyces pombe.
Cdc2, a catalytic subunit of cyclin-dependent kinases, is required for both the G1-to-S and G2-to-M transitions in the fission yeast Schizosaccharomyces pombe. Cdc13, a B-type cyclin, is required for the M-phase induction function of Cd2. Two additional B-type cyclins, Cig1 and Cig2, have been identified in S. pombe, but none of the B-type cyclins are individually required for the onset of S. We report that Cdc13 is important for DNA replication in a strain lacking Cig2. Unlike deltacdc13 cells, double-mutant deltacdc13 deltacig2 cells are defective in undergoing multiple rounds of DNA replication. The conclusion that Cig2 promotes S is further supported by the finding that Cig2 protein and Cig2-associated kinase activity appear soon after the completion of M and peak during S, as well as the observation that S is delayed in deltacig2 cells as they recover from a G1 arrest induced by nitrogen starvation. These studies indicate that Cig2 is the primary S-phase-promoting cyclin in S. pombe but that Cdc13 can effectively substitute for Cig2 in deltacig2 cells. These observations also suggest that the gradual increase in the activity of Cdc2-Cdc13 kinase can be sufficient for the correct temporal ordering of S and M phases in deltacig2 cells.
Mondesert
O
O
Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
McGowan
C H
CH
Russell
P
P
D018797:Cell Cycle Proteins / Q000235:genetics*; D019926:Cyclin B; D016213:Cyclins / Q000235:genetics*; D004261:DNA Replication; D005656:Fungal Proteins / Q000235:genetics*; D016196:S Phase / Q000235:genetics*; D012568:Schizosaccharomyces / Q000166:cytology* / Q000235:genetics; D029702:Schizosaccharomyces pombe Proteins; D014157:Transcription Factors
D018797:Cell Cycle Proteins; C080328:Cig2 protein, S pombe; D019926:Cyclin B; D016213:Cyclins; D005656:Fungal Proteins; D029702:Schizosaccharomyces pombe Proteins; D014157:Transcription Factors; C061178:cdc10 protein, S pombe