Amino acid changes provoked by streptomycin in a polypeptide synthesized in vitro.

The misincorporation of isoleucine provoked by streptomycin in a polyuridylate-directed incorporating system from Escherichia coli has been examined by a double-labeling technique with phenylalanine-(3)H and isoleucine-(14)C. The polypeptides synthesized are associated with 70S ribosomes and contain only phenylalanine in the absence of streptomycin, and both phenylalanine and isoleucine in the presence of the antibiotic. Results of acid hydrolysis and subsequent chymotryptic digestion of the polypeptides indicate that the misincorporated amino acid is inserted by peptide bonding with phenylalanine and is randomly distributed along the chain.