Genetic evidence for multiple functions of the matrix protein of vesicular stomatitis virus

TsO82, a spontaneous temperature-sensitive (ts) mutant of vesicular stomatitis virus (VSV) isolated in chick embryo fibroblasts (CEFs), complements the five prototype ts mutants of the virus. The data presented here indicate that the defect in tsO82 is localized in the M gene. The mutation changed a methionine to an arginine at position 51 of the M protein. Only true revertants could be isolated, and their frequency was low, perhaps due to the type of substitution required to return to the wild-type phenotype. TsO82 does not exhibit hypertranscription, in contrast to the data reported for all of the other ts mutants affected in the M protein. Moreover, tsO82 is conditionally ts, since it grows normally in BHK-21 cells at all temperatures. It exhibits no c.p.e. at the non-permissive temperature in CEFs. Our data argue for multiple functions of the M protein of VSV, the domain affected by the tsO82 mutation possibly being implicated both in the shut-off of cellular RNA synthesis, and for the recognition of a cellular factor required for efficient viral RNA synthesis.