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

sep1⁺ encodes a Schizosaccharomyces pombe homolog of the HNF-3/forkhead family of the tissue-specific and developmental gene regulators identified in higher eukaryotes. Its mutant allele sep1-1 causes a defect in cytokinesis and confers a mycelial morphology. Here we report on genetic interactions of sep1-1 with the M-phase initiation mutations wee1⁻, cdc2-1w, and cdc25-22. The double mutants sep1-1 wee1⁻ and sep1-1 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 by cdc25-22. We propose that the genes wee1⁺, cdc2⁺, cdc25⁺, and sep1⁺ form a regulatory link between the initiation of mitosis and the initiation of cell division.