Identification of differential regulator of mitosis and meiosis

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Involvement of the cdc2, cdc13 and cdc25 genes in meiosis in Schizosaccharomyces pombe was investigated. Using temperature- sensitive mutants and three different conditions to induce meiosis, it was found that, in contrast to the previous reports, all of these genes are required for both meiosis I and meiosis II. The cdc2 gene, which is known to be essential for the initiation of both M-phase and S-phase in mitosis, is also required for premeiotic DNA synthesis.Expression of the cdc25 and cdc13 genes was induced in concomitant with premeiotic DNA synthesis, reaching a sharp peak before the first nuclear division. Expression of cdc22 was also induced but with a peak before premeiotic DNA synthesis. The induction of cdc25 and cdc13 was hampered if DNA synthesis was inhibited, but that of cdc22 was not. The mei4 gene that is essential for meiosis is required for the induction of cdc13 and cdc25. Dependency on DNA synthesis of the induction of genes that are important for activation of p34^<cdc2> kinase has not been observed in mitosis and appears to be unique to meiosis. This may constitute a mechanism of checkpoint control in meiosis.