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

MUTATIONS in the Drosophila gene polo cause abnormal mitotic and meiotic divisions1,2. This gene encodes a 577-amino-acid protein that has an N-terminal putative kinase domain and a 300-residue C-terminal domain2. In budding yeast, a homologous kinase is encoded by CDC5 (ref. 3), a gene required for nuclear division late in the mitotic cycle4 and during meiosis5. Murine homologues have also been described6,7. Here we show that the polo gene product immunoprecipitated from extracts of single Drosophila embryos can phosphorylate casein in vitro, and that the kinase activity peaks cyclically at late anaphase/telophase. This contrasts with the cyclical activity of cyclin B-associated p34cdc2 kinase, which is maximal upon entry into mitosis during the rapid cycles of mitosis in the syncytium.