Biochemical characterization of the tsE1 mutant of vesicular stomatitis virus (New Jersey). Alterations in the NS protein.

Alterations in the NS protein of the tsE1 mutant of vesicular stomatitis virus (New Jersey serotype) appear to be responsible for its temperature-sensitive phenotype. The NS proteins of thermostable revertants of tsE1 migrated in polyacrylamide gels containing sodium dodecyl sulfate with apparent sizes which were identical to tsE1 NS, or which were 5% or 14% larger than tsE1 NS. These novel differences persisted during electrophoresis in 10% and 12.5% acrylamide gels, and in gels with gradients of acrylamide, suggesting that aberrant sodium dodecyl sulfate binding was not involved. Co-infection of cells with pairs of viruses resulted in the synthesis of both types of NS protein, suggesting that no trans-acting phenomenon was involved. Two-dimensional gel electrophoresis demonstrated that each of the NS proteins consisted of several species, but the isoelectric points of the proteins from different viruses overlapped. Furthermore, all of the NS species from a particular virus migrated with the same apparent molecular weight, suggesting that aberrant phosphorylation was not responsible for the apparent differences in size. Finally, tryptic peptide maps of amino acid and 32Pi-labeled NS proteins demonstrated that the revertant NS proteins contained all of the peptides and phosphopeptides of tsE1 NS, but each revertant NS with an apparently larger protein also contained an extra nonphosphorylated peptide. These data are consistent with the idea that the reversion of the temperature-sensitive phenotype of tsE1 can be accompanied by production of a significantly larger NS protein.