THE DROSOPHILA FS(1)YA PROTEIN, WHICH IS NEEDED FOR THE FIRST MITOTICDIVISION, IS IN THE NUCLEAR LAMINA AND IN THE ENVELOPES OF CLEAVAGE NUCLEI, PRONUCLEI, AND NONMITOTIC NUCLEI

The Drosophila melanogaster fs(1)Ya gene encodes a nuclear envelope pr otein needed to initiate embryonic cleavage divisions. In cleavage sta ge embryos the fs(1)Ya gene product is localized to the nuclear envelo pe in a cell cycle dependent manner. We show here that fs(1)Ya protein is also present in polar bodies of early cleavage stage embryos as we ll as in endoreplicating yolk nuclei. This observation suggests that t he fs(1)Ya protein is necessary but not solely responsible for embryon ic mitosis. Furthermore, cell cycle stage dependent nuclear localizati on is also seen for ectopically produced fs(1)Ya protein in tissue cul ture cells, neuroblasts, and male accessory glands, which are free of maternal products. We therefore conclude that cell cycle dependent nuc lear localization does not require any exclusively maternal products. Finally, our immunoelectron microscopy shows that the fs(1)Ya protein distribution parallels that of lamin, indicating that it is a nuclear lamina protein. (C) 1994 Academic Press, Inc.