The overall objective is to elucidate changes in the synthesis and phosphorylation of nuclear proteins during the onset of transformation in NRK cells transformed by a temperature-sensitive mutant of Rous sarcoma virus. Cells will be either prelabeled or pulse-labeled with radioisotopes during the course of transformation. Nuclear proteins will be fractionated into four discreet fractions, each of which will be analyzed by electrophoresis on SDS-polyacrylamide gels. Gels will be sliced transversely for scintillation counting and sliced longitudinally for gel autoradiography.