Functional analysis of the Drosophila CDC2 Dm gene in fission yeast.

The cdc2+ gene product (p34cdc2) is a protein kinase that regulates entry into mitosis in all eukaryotic cells. The role that p34cdc2 plays in the cell cycle has been extensively investigated in a number of organisms, including the fission yeast Schizosaccharomyces pombe. To study the degree of functional conservation among evolutionarily distant p34cdc2 proteins, we have constructed a S. pombe strain in which the yeast cdc2+ gene has been replaced by its Drosophila homologue CDC2Dm (the CDC2Dm strain). This CDC2Dm S. pombe strain is viable, capable of mating and producing four viable meiotic products, indicating that the fly p34CDC2Dm recognizes all the essential S. pombe cdc2+ substrates, and that it is recognized by cyclin partners and other elements required for its activity. The p34CDC2Dm protein yields a lethal phenotype in combination with the mutant B-type cyclin p56cdc13-117, suggesting that this S. pombe cyclin might interact less efficiently with the Drosophila protein than with its native p34cdc2 counterpart. This CDC2Dm strain also responds to nutritional starvation and to incomplete DNA synthesis, indicating that proteins involved in these signal transduction pathways, interact properly with p34CDC2Dm (and/or that p34cdc2-independent pathways are used). The CDC2Dm gene produces a 'wee' phenotype, and it is largely insensitive to the action of the S. pombe wee1+ mitotic inhibitor, suggesting that Drosophila wee1+ homologue might not be functionally conserved. This CDC2Dm strain is hypersensitive to UV irradiation, to the same degree as wee1-deficient mutants. A strain which co-expresses the Drosophila and yeast cdc2+ genes shows a dominant wee phenotype, but displays a wild-type sensitivity to UV irradiation, suggesting that p34cdc2 triggers mitosis and influences the UV sensitivity by independent mechanisms.