Abstract

All eukaryotic cellular mRNAs, and most viral mRNAs, are blocked at their 5′ ends with a cap structure (m7GpppX, where × is any nucleotide). Poliovirus, along with a small number of other animal and plant viral mRNAs, does not contain a 5′ cap structure. Since the cap structure functions to facilitate ribosome binding to mRNA, translation of poliovirus must proceed by a cap‐independent mechanism. Consistent with this, recent studies have shown that ribosomes can bind to an internal region within the long 5′ noncoding sequence of poliovirus RNA. Possible mechanisms for cap‐independent translation are discussed. Cap‐independent translation of poliovirus RNA is of major importance to the mechanism of shut‐off of host protein synthesis after infection. Moreover, it is likely to play a role in determining poliovirus neurovirulence and attenuation.