A complex between initiation factor IF2, guanosine triphosphate, and fMet-tRNA: an intermediate in initiation complex formation.

Evidence is presented that suggests the formation of a complex between polypeptide chain-initiation factor IF 2, GTP, and fMet-tRNA(f). This complex transfers both fMet-tRNA(f) and GTP to 30S ribosomal subunits in the presence of ApUpG and initiation factor IF 1. The resultant 30S initiation complex reacts with 50S subunits to form a 70S initiation complex. fMet-tRNA(f) in this 70S complex reacts with puromycin to form fMet-puromycin. These results suggest that [IF 2, GTP, fMet-tRNA(f)] is an intermediate in the initiation of protein synthesis in Escherichia coli.