Abstract
In the fission yeast Schizosaccharomyces pombe Mik1p, in combination with Wee1p, is an important inhibitor of mitosis through direct phosphorylation of Cdc2p. Here we present the observation that mik1 + is transcribed during G1- and S-phase in normally dividing cells. mik1 + transcription is regulated by the MCB–DSC1 system, which controls expression of other genes at the G1–S interval. mik1 + is shown to be an important target of MCB–DSC1 as it is epistatic for the mitotic delay phenotype displayed in cdc10-C4 cells, which are mutated in a component of DSC1. The mitotic delay in cdc10-C4 cells is bypassed by cdc2-1w, suggesting that mik1 + acts directly on cdc2 +, with no checkpoint function involved. Thus, mik1 + represents a new type of MCB–DSC1 regulated gene in fission yeast, whose gene product is exclusively expressed during G1- and S-phase to prevent premature mitosis during this cell cycle stage.
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