Abstract
Mutations in the Drosophila genes three rows (thr), fizzy (fzy), and pimples (pim) block chromosome segregation in mitosis. fzy mutations also block cyclin degradation and affected cells become permanently arrested in metaphase. Mutations in pim and thr prevent chromatid separation but proteolysis of mitotic cyclins occurs normally and cells leave mitosis. Since it has been shown that active cdc2 is required to maintain the arrest seen in fzy embryos we wished to determine if pim+ and thr+ were also required. By constructing double-mutant combinations of the three genes we have established that the fzy arrest persists in the absence of either pim or thr and that there is no synergistic interaction between pim and thr.
