Thiosine-resistant mutants of Escherichia coli K-12 with growth-medium-dependent lysyl-tRNA synthetase activity : II. Evidence for an altered lysyl-tRNA synthetase

Abstract

Studies on the lysyl-tRNA synthetase ( l-lysine : tRNA ligase (AMP), EC 6.1.1.6) from the thiosine-resistant mutants of Escherichia coli K-12 with growth-medium-dependent lysyl-tRNA synthetase activity have shown that the enzyme is an altered protein. The mutant protein is more resistant to thermal and urea denaturation than the wild-type protein. A Sephadex G-200 profile of crude extracts of the wild-type strain has revealed two forms: a major form (mol. wt. 135 000) and a minor form (mol. wt. 95 000). The profile of a mutant strain revealed a third form with a mol. wt. of 195 000, in addition to the other two.