Interaction of eukaryotic initiation factor eIF-4B with a picornavirus internal translation initiation site.

We studied the interaction of cellular proteins with the internal ribosome entry site (IRES) of foot-and-mouth disease virus by UV cross-linking and observed specific binding of a 80-kDa protein contained in cytosolic HeLa cell extract and in rabbit reticulocyte lysate. Binding of the protein was dependent on the presence of ATP. Immunoprecipitation with eIF-4B antiserum revealed that the protein is identical to the initiation factor eIF-4B. Deletions in the 3' part, but not in the 5' part, of the IRES interfered with UV cross-linking, indicating that the binding site of eIF-4B is located close to the end of the element. Attempts to separate ribosome-associated from non-ribosome-associated protein fractions of cytosolic cell extracts led to the loss of cross-linking activity. This finding suggests that additional protein factors contribute to this interaction of eIF-4B with the IRES of foot-and-mouth disease virus.