The Drosophila fs(1)Ya protein, which is needed for the first mitotic division, 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 protein needed to initiate embryonic cleavage divisions. In cleavage stage embryos the fs (1) Ya gene product is localized to the nuclear envelope 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 well as in endoreplicating yolk nuclei. This observation suggests that the fs(1)Ya protein is necessary but not solely responsible for embryonic mitosis. Furthermore, cell cycle stage dependent nuclear localization is also seen for ectopically produced fs(1)Ya protein in tissue culture cells, neuroblasts, and male accessory glands, which are free of maternal products. We therefore conclude that cell cycle dependent nuclear 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.