A CONSERVED MITOTIC KINASE ACTIVE AT LATE ANAPHASE TELOPHASE IN SYNCYTIAL DROSOPHILA EMBRYOS

MUTATIONS in the Drosophila gene polo cause abnormal mitotic and meiot ic divisions1,2. This gene encodes a 577-amino-acid protein that has a n N-terminal putative kinase domain and a 300-residue C-terminal domai n2. In budding yeast, a homologous kinase is encoded by CDC5 (ref. 3), a gene required for nuclear division late in the mitotic cycle4 and d uring meiosis5. Murine homologues have also been described6,7. Here we show that the polo gene product immunoprecipitated from extracts of s ingle Drosophila embryos can phosphorylate casein in vitro, and that t he kinase activity peaks cyclically at late anaphase/telophase. This c ontrasts with the cyclical activity of cyclin B-associated p34cdc2 kin ase, which is maximal upon entry into mitosis during the rapid cycles of mitosis in the syncytium.