Host Range Mutants of Vesicular Stomatitis Virus Defective in in vitro RNA Methylation

The viral RNA polymerase of detergent-treated vesicular stomatitis virus normally synthesizes viral mRNAs in vitro that are both guanylylated and methylated to give 5′-terminal 7mGpppAmcaps. We have characterized a virus host range mutant, hr 1, that is totally defective in vitro in the methylation of mRNA, although full-length polyadenylylated mRNAs with 5′termini of the form GpppA are synthesized in normal yields. A second mutant, hr 8, is partially defective in methylation and synthesizes mRNAs in vitro with primarily GpppA and some GpppAm5′termini. When used for in vitro translation, the unmethylated hr 1 mutant mRNA shows, as expected, reduced synthesis of viral proteins. These data provide direct evidence that the vesicular stomatitis virus-associated methyltransferase activities are virus encoded.