SWITCH FROM TRANSLATION TO RNA REPLICATION IN A POSITIVE-STRANDED RNAVIRUS

In positive-stranded viruses, the genomic RNA serves as a template for both translation and RNA replication. Using poliovirus as a model, we examined the interaction between these two processes. We show that th e RNA polymerase is unable to replicate RNA templates undergoing trans lation. We discovered that an RNA structure at the 5' end of the viral genome, next to the internal ribosomal entry site, carries signals th at control both viral translation and RNA synthesis. The interaction o f this RNA structure with the cellular factor PCBP up-regulates viral translation, while the binding of the viral protein 3CD represses tran slation and promotes negative-strand RNA synthesis. We propose that th e interaction of 3CD with this RNA structure controls whether the geno mic RNA is used for translation or RNA replication.