Methionyl transfer RNA synthetase mutants of Salmonella typhimurium which have normal control of the methionine biosynthetic enzymes

Dominance of the Wild-type Alleles of Methionine Regulatory Genes in Salmonella typhimurium

“…This conclusion has recently been confirmed by the identification of a gene specifying methionine permease, which is located far from metK on the linkage map (P. D. Ayling & E. S. Bridgeland, personal communication). Lawrence et al (1968) were able to reject the possibility that the metK gene product was an apo-repressor; and Cross & Rowbury (1969) showed that methionyl-tRNA was unlikely to have any effect on regulation, while methionyl-tRNA synthetase was specified by the metG gene. Thus conventional explanations for the metK phenotype all appear inadequate, and it is necessary to look for a feature of methionine biosynthesis that is not shared by other well-established biosynthetic systems.…”

“…Ethionine inhibits the growth of bacteria by replacing methionine in protein synthesis (Spizek & Janecek, 1969): it has no effect on S-adenosylmethionine synthesis (Cox & Smith, 1969;Gross, 1969) and little effect on the activity of the methionine first enzyme (D. A. Lawrence, personal communication). Thus the ethione resistance of metJ mutants is probably the result of reduced incorporation of the analogue into proteins, attributable to the high intracellular methionine level.…”

Aminoacyl‐tRNA Synthetases: Some Recent Results and Achievements

“…Strains with damaged synthetases were found among E. coli mutants-histidine (280), tryptophan (28 1-284), tyrosine (285), glycine (273,279), serine (286), and isoleucine (267) auxotrophs. The mutants of Salmonella typhimurium that do not grow in the absence of exogenous methionine (287) and isoleucine (288) contain altered aminoacyl-tRNA synthetases for these amino acids; the tryptophan auxotroph of eukaryote N . crass(^ contains a defective tryptophanyl-tRNA synthetase (289).…”

“…The K , value of the mutant enzyme can sometimes be only a few times greater than that of the normal one [e.g., two to three times in the case of tryptophanyl-tRNA synthetases from Neurosfiora (289) and E. coli (282)], whereas in many cases it becomes several orders of magnitude greater [e.g., mutant methionyl-and isoleucyl-tRNA synthetases from S. lyphimurzum (287,288) and mutant isoleucyl-tRNA synthetase from E. coli (267)l. An increase in the K , value means a decrease in the rate of the acylation of the corresponding tRNA by the amino acid at the normal endogenous level of the latter; increase in the amino acid endogenous level after the addition of the amino acid to the medium results in an increased rate of a,cylation and thus in normalization of the growth.…”

“…These are the h i d gene of histidyl-tRNA synthetase (79 min, between guaA and strB) (296), the leuS gene of leucyl-tRNA synthetase (18 min, near the gal locus (31), and the ilvS gene of isoleucyl-tRNA synthetase (between pyrA and thr) (288). Mutations of S. typhimurium are also described at the metG gene (67 min), resulting in methionine auxotrophy (325); recent studies demonstrated that metG is the structural gene of methionyl-tRNA synthetase (287). Knowledge of the location of structural genes of enzymes on genetic maps is sometimes useful in the solution of some practical problems.…”