THE DROSOPHILA CELL-CYCLE GENE FIZZY IS REQUIRED FOR NORMAL DEGRADATION OF CYCLIN-A AND CYCLIN-B DURING MITOSIS AND HAS HOMOLOGY TO THE CDC20 GENE OF SACCHAROMYCES-CEREVISIAE

The Drosophila cell cycle gene fizzy (fzy) is required for normal exec ution of the metaphase-anaphase transition. We have cloned fzy, and co nfirmed this by P-element mediated germline transformation rescue. Seq uence analysis predicts that fzy encodes a protein of 526 amino acids, the carboxy half of which has significant homology to the Saccharomyc es cerevisiae cell cycle gene CDC20. A monoclonal antibody against fly detects a single protein of the expected size, 59 kD, in embryonic ex tracts. In early embryos fly is expressed in all proliferating tissues ; in late embryos fly expression declines in a tissue-specific manner correlated with cessation of cell division. During interphase fly prot ein is present in the cytoplasm; while in mitosis fly becomes ubiquito usly distributed throughout the cell except for the area occupied by t he chromosomes. The metaphase arrest phenotype caused by fzy mutations is associated with failure to degrade both mitotic cyclins A and B, a nd an enrichment of spindle microtubules at the expense of astral micr otubules. Our data suggest that fly function is required for normal ce ll cycle-regulated proteolysis that is necessary for successful progre ss through mitosis.