Initiation factor IF-3-dependent binding of Escherichia coli ribosomes and N-formylmethionine transfer-RNA to rabbit globin messenger.

An initiation complex has been formed in high yields from E. coli ribosomes, 9S messenger RNA for rabbit hemoglobin, and N-formylmethionine-tRNA. Initiation factor IF-3 is required for the binding and puromycin is required for the release of fMet. Valyl-tRNA fails to bind to the second codon, whereas a mixture of 15 aminoacyl-tRNAs promotes incorporation. Together with quantitative data, the findings suggest that IF-3 directs the ribosomes to an AUG codon on one of the two globin messengers, at a site that is different from the normal starting point for globin synthesis.