Association of Rabies Virus Nominal Phosphoprotein (P) with Viral Nucleocapsid (NC) Is Enhanced by Phosphorylation of the Viral Nucleoprotein (N)

We investigated possible role(s) of N protein phosphorylation in the rabies virus replication process. A large amount of P proteins are associated with the viral nucleocapsid (NC) in the infected cell, the amount which was greatly decreased by phosphatase-treatment of the isolated NC, indicating that the phosphate group of N and/or P proteins is essential for their stable association with the NC. Immunoprecipitation studies were performed on the coexpressed normal N or phosphorylation deficient N(S389A) and P proteins, demonstrating that the P protein associated with phosphorylation-deficient NC-like structures was much less in amount than that associated with the wild type NC. Similar results were also obtained with a mutant P protein, PDeltaN19, which lacked the N-terminal 19 amino acids and was capable of binding to the NC-like structures but incapable of forming the RNA-free N-P complexes. Immunoprecipitation studies with mAb #402-13 further suggested that the NC-specific linear 402-13 epitope was exposed even on the P proteins which were associated with the phosphorylation-deficient NC-like structures, but such association was very weak as demonstrated by greatly decreased amounts of coprecipitated NC-like structures. From these results, we assume that the phosphorylation of N protein enhances the association between the 402-13 epitope-positive P protein and the NC probably by stabilizing such P-NC binding.