FUNCTIONAL-ANALYSIS OF THE DROSOPHILA CDC2 DM GENE IN FISSION YEAST

The cdc2(+) gene product (p34(cdc2)) is a protein kinase that regulate s entry into mitosis in all eukaryotic cells. The role that p34(cdc2) plays in the cell cycle has been extensively investigated in a number of organisms, including the fission yeast Schizosacchar omyces pombe. To study the degree of functional conservation among evolutionarily di stant p34(cdc2) proteins, we have constructed a S. pombe strain in whi ch the yeast cdc2(+) gene has been replaced by its Drosophila homologu e CDC2Dm (the CDC2Dm strain). This CDC2Dm S. pombe strain is viable, c apable of mating and producing four viable meiotic products, indicatin g that the fly p34(CDC2Dm) recognizes all the essential S. pombe cdc2( +) substrates, and that it is recognized by cyclin partners other elem ents required for its activity. The (CDC2Dm) protein yields a lethal p henotype in combination with the mutant B-type cyclin p56(cdc13-117), suggesting that this S. pombe cyclin might interact less efficiently w ith the Drosophilla protein than with its native p34(cdc2) counterpart . This CDC2Dm strain also responds to nutritional starvation and to in complete DNA synthesis, indicating that proteins involved in these sig nal transduction pathways, interact properly with p34(CDC2Dm) (and/or that p34(cdc2)-independent pathways are used). The CDC2Dm gene produce s a 'wee' phenotype, and it is largely insensitive to the action of th e S. pombe weel(+) mitotic inhibitor, suggesting that Drosophila weel homologue might not be functionally conserved. This CDC2Dm strain is hypersensitive to UV irradiation, to the same degree as weel-deficient mutants. A strain which co-expresses the Drosophila and yeast cdc2(+) genes shows a dominant wee phenotype, but displays a wild-type sensit ivity to UV irradiation, suggesting that p34(cdc2) triggers mitosis an d influences the UV sensitivity by independent mechanisms.