Recognition of eukaryotic mRNAs by the 43S pre-initiation complex begins with the recognition of the 5' cap found at the end of most eukaryotic mRNAs. Recognition is mediated by a three-subunit protein called eIF4F (see Figure 14-27b). One of the three subunits binds directly to the 5' cap and the other two subunits bind non-specifically to the associated RNA. This complex is joined by eIF4B which activates an RNA he!¡case in one of the eIF4F subunits. The he-licase unwinds any secondary structures (such as hairpins) that may bave formed at the end of the mRNA. Removal of secondary structures is critical as the 5' end of mRNA must bo unstructured to bind to the small subunit. The elF4F/B bound unstructured mRNA recruits the 43S pre-initiation complex to the mRNA through inter-actions between eIF4F and eIF3.

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