PHOSPHORYLATION AND LOCALIZATION OF REPLICATION PROTEIN-A DURING OOGENESIS AND EARLY EMBRYOGENESIS OF DROSOPHILA-MELANOGASTER

The phosphorylation and localization of Drosophila melanogaster Replic ation Protein A (DRP-A) was examined during oogenesis and in single em bryos during the syncytial nuclear divisions of embryogenesis. DRP-A f rom ovaries was separated by two-dimensional electrophoresis into mult iple phosphorylated species that include a previously unresolved form of RP-A. These forms are developmentally regulated with a major phosph orylated form appearing at stage 11 of oogenesis and persisting into m ature eggs. Actively cycling early embryos were examined to investigat e DNA replication in the absence of repair synthesis due to perturbati on by drugs or mutation. An oscillation of the two major forms of DRP- A was observed over multiple cell cycles. The phosphorylated form was most abundant at mitosis and the nonphosphorylated form at interphase. In contrast to other systems where a phosphorylated form of RPA has b een correlated with S phase, only the nonphosphorylated form of Drosop hila RP-A is observed in early Drosophila embryos during DNA replicati on. Consistent with this role in DNA metabolism, DRP-A was localized t o the nucleus. Subsequently at mitosis, DRP-A becomes delocalized. Str ikingly, in ovaries a relatively large amount of DRP-A was observed du ring the early mitotic stages of oogenesis. (C) 1995 Academic Press, I nc.