Specificity of the amino acid transfer reaction inE. coli strains carrying different alleles of the RNA control (RC) gene

Summary The idea has been tested here that the aberration in amino acid controlled regulation of RNA synthesis in a mutant strain ofE. coli might reflect a major breakdown in the specificity of transfer of amino acids to S-RNA. For this purpose, S-RNA and amino acid activating enzymes were extracted from bacteria carrying either the normalRC^st or the aberrantRC^rel allele of the RNA control gene. The purified S-RNA preparations were first charged enzymatically with one or more of the 20 standard amino acids, then oxidized with periodate, and finally reisolated and retested for their residual capacity to accept an amino acid that was absent from the preliminary charging mixture. If preliminary charging transferred an amino acid to a non-cognate S-RNA species belonging to an absent amino acid, then the acceptor capacity for the missing amino acid would survive periodate oxidation and reveal its presence on recharging with that amino acid after post-periodate reisolation of the S-RNA. The results presented here show that there does not appear to exist any such major breakdown of transfer specificity in eitherRC^st orRC^rel bacteria: preliminary charging of the S-RNA fromRC^rel bacteria with 19 of the 20 standard amino acids by use of the homologous amino acid activating enzymes does not afford protection against periodate oxidation for any appreciable fraction of the acceptor capacity for the absent 20th amino acid (when that amino acid is either methionine or arginine). It is unlikely, therefore, that thecatholic inducer, postulated to explain the continued RNA synthesis ofRC^rel amino acid auxotrophs in the absence of their growth requirement, is one of the 20 standard amino acids.This investigation was supported by Public Health Service Research Grant CA 02129, from the National Cancer Institute.