Effect of S-adenosylmethionine on human rotavirus RNA synthesis

The characteristics of human rotavirus-associated RNA polymerase activity have been examined in relation to the effects of ribonucleoside triphosphate analogs and S-adenosylmethionine. These effects were analyzed by testing two forms of activated virus particles: EDTA- and heat-treated virions. The former lack outer shell proteins, and activation by means of heat treatment does not introduce any apparent modification in virion structure. Virus-associated RNA polymerase shows similar properties in both preparations, suggesting that outer proteins are not directly involved in RNA synthesis. Transcription in this virus is specifically dependent on a hydrolyzable form of ATP. Such a requirement is not overcome by preincubation or by the addition of S-adenosylmethionine, suggesting a hypothetical mechanism that couples transcription to ATP hydrolysis. The addition of S-adenosylmethionine stimulated transcription and diminished the Km value not only for ATP but also for the other three ribonucleoside triphosphates. Analysis of methylated RNA products suggested that methyl groups were incorporated into all of the RNA species synthesized by virion-associated polymerase. Further analysis of those RNA molecules showed that they contained cap structures at the 5' end. The results suggest that the cap structure at the end of RNA molecules may enable RNA polymerase to elongate transcripts more efficiently, in a reaction in which the hydrolysis of ATP is involved.