Component of the protein complex eIF4F, which is involved in the recognition of the mRNA cap, ATP-dependent unwinding of 5'-terminal secondary structure and recruitment of mRNA to the ribosome (PubMed:29987188). Exists in two complexes, either with EIF1 or with EIF4E (mutually exclusive) (PubMed:29987188). Together with EIF1, is required for leaky scanning, in particular for avoiding cap-proximal start codon (PubMed:29987188). Together with EIF4E, antagonizes the scanning promoted by EIF1-EIF4G1 and locates the start codon (through a TISU element) without scanning (PubMed:29987188). As a member of the eIF4F complex, required for endoplasmic reticulum stress-induced ATF4 mRNA translation (PubMed:29062139). {ECO:0000269|PubMed:29062139, ECO:0000269|PubMed:29987188}. This is the function of EIF4G1 (eukaryotic translation initiation factor 4 gamma 1, Ensembl gene identifier ENSG00000114867).