A NOVEL MUTATION INVOLVED IN THE MITOTIC CHECKPOINT IN THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE

The cps8 mutation which confers supersensitivity to a spindle poison, Isopropyl N-3-chlorophenyl carbamate (CIPC), in the fission yeast Schi zosaccharomyces pombe was investigated. The cps8 mutant accumulated en larged multinucleate cells in the stationary phase under normal growth conditions. The mutant was highly lethal at 36.5-degrees-C in a fresh growth medium but not in a saline solution where the cell cycle cease s quickly. Lethality at high temperature was significantly suppressed by cdc1 or nda2 mutation which blocks nuclear division, but not by hyd roxyurea treatment or cdc22 mutation which blocks DNA synthesis. A cdc 10 cps8 double mutant remained lethal to high temperature, suggesting this double mutant to bypass the requirement for cdc10+ indispensable for the cell cycle start in a wild-type cell. After being transferred to a fresh medium at 36.5-degrees-C, the multinucleate cells rapidly d ivided with aberrant nuclear segregation. Thus, cps8 mutation allows c ells to undergo mitosis without DNA replication at the restrictive tem perature. The cps8 gene was mapped on the left arm of chromosome II cl osely linked to but distinct from cdc2 locus.