CHARACTERIZATION OF A DROSOPHILA PHOSPHORYLATION-DEPENDENT NUCLEAR-LOCALIZATION-SIGNAL-BINDING PROTEIN

A 94 kDa nuclear-localization-signal (NLS)-binding protein was purifie d from Drosophila embryos. The NLS of the simian-virus-40 T-antigen is specifically bound by the dephosphorylated form of the protein. After phosphorylation, the affinity of the protein for the NLS is sharply d ecreased. In the dephosphorylated form, p94 (protein of 94 kDa) is the major NLS-binding protein in Drosophila embryos. Immunoprecipitation confirmed the ATP-dependent phosphorylation of p94, and co-precipitati on of two additional phosphorylated proteins, indicated that the NLS-b inding protein is part of a larger complex in Drosophila embryos. In a greement with the immunoprecipitation results, cross-linking experimen ts demonstrated the interaction of p94 with three additional proteins. These protein-protein interactions were also phosphorylation-dependen t.