Phosphorylation of Sendai virus phosphoprotein by cellular protein kinase C zeta

The phosphoproteins (P) of nonsegmented negative strand RNA viruses are viral RNA polymerase subunits involved in both transcription and replication during the virus life cycle. Phosphorylation of P proteins in several negative strand RNA viruses by specific cellular kinases was found to be required for P protein function. In the present study, using bacterially expressed unphosphorylated P protein of Sendai virus, a mouse parainfluenza virus, we have shown that the major cellular kinase that phosphorylates P protein in vitro is biochemically and immunologically indistinguishable from protein kinase C (PKC) zeta isoform. PKC zeta was packaged into the Sendai virion and remained associated with purified viral ribonucleoprotein, where it phosphorylated both the P and the nucleocapsid protein in vitro. When PKC zeta-specific inhibitory pseudosubstrate peptide was introduced into LLC-MK2 cells prior to Sendai virus infection, production of progeny virus was dramatically attenuated, and kinetic analysis revealed that primary transcription was repressed. These data indicate that phosphorylation of the Sendai virus P protein by PKC zeta plays a critical role in the virus life cycle.