A further study of misreading of codons induced by streptomycin and neomycin using ribopolynucleotides containing two nucleotides in alternating sequence as templates

Abstract

The effect of streptomycin and neomycin on the translation of poly UG, poly AG, poly UC and poly AC, which contain the two specified nucleotides in alternating sequence, has been studied. The misreading of codons in these polynucleotides is more specific than that found previously in work with homopolynucleotides. With poly UG, streptomycin induces the incorporation of arginine and some serine in addition to the normal incorporation of valine and cysteine. With poly UC, streptomycin induces the incorporation of phenylalanine, proline and some histidine in addition to the normal incorporation of leucine and serine. Streptomycin causes no misreading of poly AC or poly AG, although the normal incorporations directed by these polymers are inhibited. From these results, the following conclusions are drawn regarding the action of streptomycin: (1) only the two pyrimidine bases are misread; (2) pyrimidine bases in the 5′-terminal position of a codon are misread as pyrimidines; (3) internal pyri-midines can be misread as both pyrimidines and purines; and (4) misreading of a base is influenced considerably by the nature of the neighboring base. Misreading by neomycin is much less specific than that induced by streptomycin, evidence being obtained, in some cases, of misreading of two bases in the same codon.