Suppression of a defective alanyl-tRNA synthetase in Escherichia coli: a compensatory mutation to high alanine affinity
- PMID: 340903
- DOI: 10.1007/BF00283495
Suppression of a defective alanyl-tRNA synthetase in Escherichia coli: a compensatory mutation to high alanine affinity
Abstract
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).
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