Requirement of initiation factor 3 in the initiation of polypeptide synthesis with N-acetylphenylalanyl-tRNA

Initiation factor 3 is required, along with initiation factors 1 and 2, for the incorporation of N-acetylphenylalanine into polypeptides and the formation of N-acetylphenylalanylpuromycin. Initiation factor 3 also strongly stimulates the binding of N-acetylphenylalanyl transfer RNA to isolated 30S ribosomal subunits. Phosphocellulose fractions of initiation factor 3 were found to catalyze N-acetylphenylalanine incorporation differentially with different synthetic messenger RNAs not containing any codons for N-formylmethionine. The results suggest that ribosomes recognize the initiator codon only through the initiator transfer RNA.