Regulation of the cell cycle timing of Start in fission yeast by the rum1+ gene

We have identified the rum1(+) gene as a new regulator of the G(1)-phase of the fission yeast cell cycle. rum1(+) determines the cell cycle timing of Start, by maintaining cells in a pre-Start state until they have attained a minimal critical mass. Cells lacking rum1(+) are unable to arrest in pre-Start G(1) in response to nitrogen starvation and are subsequently sterile. In addition, rum1(+) prevents entry into mitosis from pre-Start G(1), as shown by the fact that cdc10 mutants in the absence of rum1(+) undergo lethal mitosis without entering S-phase.