Initiation factor elF5B catalyzes second GTP-dependent step in eukaryotic translation initiation

摘要

Initiation factors IF2 in bacteria and elF2 in eukaryotes are GTPases that bind Met-tRNA_i~(Met) to the small ribosomal subunit. elF5B, the eukaryotic ortholog of IF2, is a GTPase that promotes ribosomal subunit joining. Here we show that elF5B GTPase activity is required for protein synthesis. Mutation of the conserved Asp-759 in human elF5B GTP-binding domain to Asn converts elF5B to an XTPase and introduces an XTP requirement for subunit joining and translation initiation. Thus, in contrast to bacteria where the single GTPase IF2 is sufficient to catalyze translation initiation, eukaryotic cells require hydrolysis of GTP by both elF2 and elF5B to complete translation initiation.