Plays a role in translation initiation (PubMed:10659855, PubMed:35732735). Ribosome-dependent GTPase that promotes the joining of the 60S ribosomal subunit to the pre-initiation complex to form the 80S initiation complex with the initiator methionine-tRNA in the P-site base paired to the start codon (PubMed:10659855, PubMed:35732735). Together with eIF1A (EIF1AX), actively orients the initiator methionine-tRNA in a conformation that allows 60S ribosomal subunit joining to form the 80S initiation complex (PubMed:12569173, PubMed:35732735). Is released after formation of the 80S initiation complex (PubMed:35732735). Its GTPase activity is not essential for ribosomal subunits joining, but GTP hydrolysis is needed for eIF1A (EIF1AX) ejection quickly followed by EIF5B release to form elongation- competent ribosomes (PubMed:10659855, PubMed:35732735). In contrast to its procaryotic homolog, does not promote recruitment of Met-rRNA to the small ribosomal subunit (PubMed:10659855). {ECO:0000269|PubMed:10659855, ECO:0000269|PubMed:12569173, ECO:0000269|PubMed:35732735}. This is the function of EIF5B (eukaryotic translation initiation factor 5B, Ensembl gene identifier ENSG00000158417).