Temperature-sensitive mutants of vesicular stomatitis virus: comparison of the in vitro RNA polymerase defects of group I and group IV mutants.

When tested in vitro, certain temperature-sensitive (ts) mutants of vesicular stomatitis virus (VSV) belonging to complementation groups I and IV appear to have defects in the virion-bound polymerase. To obtain further information concerning the nature of these defects, representative mutants were dissociated by the method of S. Emerson and R. Wagner (1972), and their supernatant (S) and pellet (P) fractions were tested for transcriptase activity when combined with the P and S fractions, respectively, of VSV-HR virions. It was found that the S fractions from group I mutants tsW4, 11, 14, 15, and 28 were defective in transcriptase activity, whereas their P fractions were as active as those of VSV-HR. On the other hand, the P fraction derived from virions of the group IV mutant tsW16B showed reduced activity at 25 C and very little activity at 38 C. These results suggest that our group I mutants, like those examined by D. Hunt and R. Wagner (1974), have a defect in the soluble transcriptase enzyme, whereas mutant tsW16B (group IV) has a defect in a sedimentable component required for transcriptase activity, possibly in the ribonucleoprotein template.