Examination of the mode of action of ribavirin against tobacco mosaic virus.

Ribavirin inhibited a specific step of tobacco mosaic virus (TMV) replication. Time-courses of sensitivity of TMV multiplication in asynchronous and synchronous infections demonstrated that ribavirin inhibited an early function that occurs prior to the period of viral RNA and protein synthesis. In the synchronous infection, ribavirin inhibited the synthesis of both single-stranded genomic RNA and double-stranded replicative form RNA when treatment began during the first 4 h, but there was no inhibition when treatment began at 12 h or later, even though most RNA synthesis occurred after 12 h. Viral protein synthesis also was inhibited when treatment began during the first 4 h and not when treatment began later. Unlike the mechanisms proposed against animal viruses, ribavirin appears to inhibit TMV replication by preventing an early function that is necessary to initiate viral RNA synthesis.