Interferon action on parental Semliki forest virus ribonucleic acid

Actinomycin D-treated chick fibroblasts were infected with purified 32 P-labeled Semliki forest virus, and ribonucleic acid (RNA) was extracted after 1 or 2 hr. Within 1 hr, viral RNA forms sedimenting in sucrose gradients at 42 S , 30 S , and 16 S were present. The 42 S form corresponded to the RNA of the virion. The 16 S form appeared to be a double-stranded template for the formation of new viral RNA, since nascent RNA was associated with it and the molecule could be heat-denatured and subsequently reannealed by slow cooling. Interferon treatment before infection, or puromycin (50 μg/ml) or cycloheximide (200 μg/ml) added at the time of virus infection, had no effect on the formation of the 30 S RNA but inhibited the production of the 16 S form. Several findings made it unlikely that these results were due to breakdown of parental RNA and reincorporation of 32 P into progeny structures. The results suggested that the mechanism of interferon action involves inhibition of protein synthesis by parental viral RNA, since a specific viral RNA polymerase had previously been demonstrated to be necessary for production of 16 S RNA. No protein synthesis appears necessary for formation of 30 S RNA from parental virus RNA.