Component of the 43S pre-initiation complex (43S PIC), which binds to the mRNA cap-proximal region, scans mRNA 5'-untranslated region, and locates the initiation codon. In this complex, acts as a GTPase-activating protein, by promoting GTP hydrolysis by eIF2G (EIF2S3). During scanning, interacts with both EIF1 (via its C-terminal domain (CTD)) and EIF1A (via its NTD). This interaction with EIF1A contributes to the maintenance of EIF1 within the open 43S PIC. When start codon is recognized, EIF5, via its NTD, induces eIF2G (EIF2S3) to hydrolyze the GTP. Start codon recognition also induces a conformational change of the PIC to a closed state. This change increases the affinity of EIF5-CTD for EIF2-beta (EIF2S2), which allows the release, by an indirect mechanism, of EIF1 from the PIC. Finally, EIF5 stabilizes the PIC in its closed conformation.
Subcellular locations: Cytoplasm