Functional interaction of translation initiation factor eIF4G with the foot-and-mouth disease virus internal ribosome entry site

In the life-cycle of picornaviruses, the synthesis of the viral polyprotein is initiated cap-independently at the internal ribosome entry site (IRES) far downstream from the 5' end of the viral plus-strand RNA. The cis-acting IRES RNA elements serve as binding sites for translation initiation factors that guide the ribosomes to an internal site of the viral RNA. In this study, we show that the eukaryotic translation initiation factor eIF4G interacts directly with the IRES of foot-and-mouth disease virus (FMDV). eIF4G binds mainly to the large Y-shaped stem-loop 4 RNA structure in the 3' region of the FMDV IRES element, whereas stem-loop 5 contributes only slightly to eIF4G binding. Two subdomains of stem-loop 4 are absolutely essential for eIF4G binding, whereas another subdomain contributes to a lesser extent to binding of eIF4G. At the functional level, the translational activity of stem-loop 4 subdomain mutants correlates with the efficiency of binding of eIF4G in the UV cross-link assay. This indicates that the interaction of eIF4G with the IRES is crucial for the initiation of FMDV translation. A model for the interaction of initiation factors with the IRES element is discussed.