Control of Arginine Biosynthesis in Escherichia coli : Role of Arginyl-Transfer Ribonucleic Acid Synthetase in Repression

Abstract

The physiological role of arginyl-transfer ribonucleic acid (Arg-tRNA) synthetase (E.C. 6.1.1.13, arginine: RNA ligase adenosine monophosphate) in repression of arginine biosynthetic enzymes was examined. Mutants with nonrepressible synthesis of arginine biosynthetic enzymes were isolated from various strains of Escherichia coli by resistance to growth inhibition by canavanine, an arginine analogue. These mutants possessed reduced Arg-tRNA synthetase activities which were qualitatively different from the synthetase activity of the wild type. The mutant enzymes exhibited turnover in vivo and were less stable in vitro than the wild type at both 4 C and 40 C; they possessed different affinities for both arginine and canavanine as measured by the three common assay systems for aminoacyl-tRNA synthetases. Furthermore, in one case it was shown that (i) the mutant possesed unaltered uptake of arginine, and (ii) that the mutant possessed diminished ability to incorporate canavanine into proteins and to attach canavanine to tRNA. These observations suggested that the mutation to canavanine resistance involved a structural change in Arg-tRNA synthetase. Likewise, the results of genetic experiments suggested that the mutants differed from the wild-type strain at only one locus, and that this lies in the region of the chromosomes that includes a structural gene for Arg-tRNA synthetase. It appears that Arg-tRNA synthetase may be involved in some way in repression by arginine of its own biosynthetic enzymes.