Coordination of Initiation of Nuclear Division and Initiation of Cell Division in Schizosaccharomyces pombe : Genetic Interactions of Mutations

sep1+ encodes aSchizosaccharomyces pombe homolog of the HNF-3/forkhead family of the tissue-specific and developmental gene regulators identified in higher eukaryotes. Its mutant allelesep1-1 causes a defect in cytokinesis and confers a mycelial morphology. Here we report on genetic interactions ofsep1-1 with the M-phase initiation mutationswee1− ,cdc2-1w , andcdc25-22 . The double mutantssep1-1 wee1− andsep1-1 cdc2-1w form dikaryon cells at high frequency, which is due to nuclear division in the absence of cell division. The dikaryosis is reversible and suppressible bycdc25-22 . We propose that the geneswee1+ ,cdc2+ ,cdc25+ , andsep1+ form a regulatory link between the initiation of mitosis and the initiation of cell division.