Translational enhancement of the poliovirus 5' noncoding region mediated by virus-encoded polypeptide 2A.

Genetic and biochemical studies have revealed that the 5' noncoding region of poliovirus mediates translation of the viral mRNA by an unusual mechanism involving entry of ribosomes in internal sequences of mRNA molecules. We have found that mRNAs bearing the 5' noncoding region of poliovirus were translated at an enhanced rate in poliovirus-infected mammalian cells at a time when translation of cellular mRNAs was not yet inhibited. This translational enhancement of the polioviral 5' noncoding region was mediated by the expression of virus-encoded polypeptide 2A. This indicates that 2A is a multifunctional protein involved directly or indirectly in the activation of viral mRNA translation, in addition to its known roles in viral polyprotein processing and in inhibition of cellular protein synthesis. Thus, 2A represents an activator of translation of a viral mRNA that is translated by an internal ribosome binding mechanism. A likely consequence of this role of 2A is the efficient translation of viral mRNAs early in the infectious cycle, when host cell mRNAs can still compete with viral mRNAs for the host cell translation apparatus.