Structural and mechanistic insights into translation initiation on the enterovirus Type 1 IRES

Enteroviruses are a diverse group of pathogens that cause over one billion human infections annually. Upon cell entry, translation of the viral genome is directed by an internal ribosome entry site (IRES) within the 5' untranslated region. Despite early identification of the Type 1 poliovirus IRES, the structural and mechanistic basis for its activity remains poorly understood due to its size, flexibility and dependence on multiple host cell factors. Here, we reconstitute human translation initiation on a model poliovirus IRES and examine 48S complexes by cryo-electron microscopy. Our structures reveal how IRES domain IVc contacts ribosomal proteins uS19 and uS13, whilst a conserved GNRA tetraloop engages with the initiator tRNA during start-codon recognition. Disruption of these interfaces impairs IRES-dependent translation and viral replication. Together, our results provide new structural and mechanistic insights into initiation on the Type 1 IRES and reveal conserved RNA-RNA interactions critical for enterovirus translation.