Phosphorylation of the mouse hepatitis virus nucleocapsid protein.

Analysis of the radiolabeled tryptic peptides derived from the nucleocapsid proteins of two serotypes of mouse hepatitis virus showed each to have a small number of unique peptides; however, two biologically distinct variants of the JHM strain appeared identical. Analysis of [32P]-labeled nucleocapsid-derived peptides showed that phosphorylation occurs at only a few sites and that all three viruses differed in the sites of phosphorylation. No differences in the sites of phosphorylation were found between the nucleocapsid proteins derived from purified virions and the membranes or the cytosol of infected cells, suggesting that post-translational phosphorylation plays no role in the regulation of viral assembly. These data show unequivocal evidence that the nucleocapsid proteins of mouse hepatitis virus strains differ in the sites of phosphorylation.