Suppression of a defective alanyl-tRNA synthetase in Escherichia coli: a compensatory mutation to high alanine affinity.
Among temperature resistant revertants of a temperature sensitive E. Coli alanyl-tRNA synthetase mutant a strain was found which contains an alanyl-tRNA synthetase with an additional mutation in the structural gene of the enzyme. This mutant enzyme has a 9 or 38 fold decreased Km value for alanine compared to that of the thermolabile parental enzyme or to wild-type enzyme, respectively. The alaS gene maps just counterclockwise from recA on the E. coli map (94% cotransduction frequency). It appears that the enzyme's increased affinity for alanine is the mechanism of suppressing the temperature sensitive character of the cell. In addition, some cold-sensitive temperature resistant revertants were found, where the cold-sensitive character mapped near strA. Presumably they are due to changes in ribosomal proteins as characterized by Ruffler et al. (1974).
D000409:Alanine / Q000378:metabolism; D000412:Alanine-tRNA Ligase / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D001426:Bacterial Proteins / Q000096:biosynthesis; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005796:Genes; D006358:Hot Temperature; D007700:Kinetics; D009154:Mutation; D013489:Suppression, Genetic
D000596:Amino Acids; D001426:Bacterial Proteins; D000604:Amino Acyl-tRNA Synthetases; D000412:Alanine-tRNA Ligase; D000409:Alanine