Induction of a novel protein kinase in pupae of the silkworm Bombyx mori after infection with nuclear polyhedrosis virus

Protein kinases induced by Bombyx mori nuclear polyhedrosis virus in pupae of the silkworm B. mori were examined by activity gel analysis using phosvitin as a protein substrate. The method involved PAGE of the soluble fraction from pupae under native conditions and in the presence of SDS, followed by in situ renaturation of proteins and recovery of protein kinase activity in the intact gel. A novel protein kinase able to phosphorylate phosvitin was detected in the infected pupae from 2 days post-infection. This enzyme was not present in uninfected silkworms at any stage of the pupal period. The novel kinase activity was found by SDS-PAGE to be associated with a single polypeptide with an apparent Mr of 50K. However, on electrophor-esis under native conditions its activity was associated with a set of polypeptides with similar but not identical electrophoretic mobilities. Microheterogeneity of the catalytically active polypeptides suggests that the virus-induced protein kinase undergoes post-translational modification during the course of infection. Protein phosphorylation plays a key role in the regulation of cellular metabolism and viral oncogenesis. Although the function of protein kinases in the reproduction of viruses is less clear, specific protein kinases have been found associated with virions of many RNA and DN