Vesicular stomatitis virus mRNA methylation in Vivo: Effect of cycloleucine, an inhibitor of S-adenosylmethionine biosynthesis, on viral transcription and translation

Abstract

Cycloleucine is a potent and specific inihibitor of S-adenosylmethionine biosynthesis and subsequent RNA methylations in Chinese hamster ovary (CHO) cells. When added in the course of an infection of CHO cells with vesicular stomatitis virus (VSV), cycloleucine does not significantly modify the rate of viral RNA and protein synthesis or the production of mature particles. Under the same conditions cycloleucine will reduce by 83% the methyolation of newly synthesized polyadenylated 11–16 S viral RNA. The mode of action of cycloleucine and cycloheximide are clearly distinguishable under these conditions. In contrast when cells are treated with cycloleucine, immediately after virus adsorption, the effect on viral RNA synthesis is very similar to that of cycloheximide. That is, a 90% inhibition in the production of viral messenger RNAs is observed along with a complete disappearance of newly synthesized 38 S RNA species, suggesting that secondary transcription is inhibited. Viral protein synthesis and virus production are similarly inhibited during this period. The undermethylated mRNAs of VSV synthesized in the presence of cycloleucine are 80% undertranslated as compared to mRNAs synthesized in untreated cells. Our results suggest that mRNA methylation in VSV is required for translation in vivo. The mode of action of cycloleucine during the infectious process is discussed.