Proteins of vesicular stomatitis virus. V. Identification of a precursor to the phosphoprotein of Piry virus.

A metabolic precursor to the major phosphoprotein of Piry virus (NSv) has been identified in extracts of Piry virus-infected L cells. The conversion of the precursor NSi to NSv occurs with a half-life of 20 min and is independent of continued protein synthesis. NSi has a greater electrophoretic mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis than does the product NSv, suggesting an increase in molecular weight during maturation. The conversion is unaffected by cyclic AMP, cyclic GMP, or by theophilline and cordycepin. No decrease in isoelectric point of NSv relative to NSi was observed on isoelectric focusing acrylamide gels. These latter observations suggest that NSi and NSv do not differ in extent of phosphorylation. We also report, without further characterization, the identification of another phosphoprotein in Piry virus-infected cells having an electrophoretic mobility in sodium dodecyl sulfate-polyacrylamide gel electrophoresis just slightly greater than the nucleocapsid N protein.