Abstract
An arginine regulatory mutant (i.e., mutated in the argR gene) has been isolated from a strain of Salmonella typhimurium LT2. The argR mutant was found to excrete arginine into the growth medium with glycerol but not glucose as carbon source. Constitutive synthesis of arginine biosynthetic enzymes was observed. Whereas previous results (A. T. Abd-E1-A1 and J. L. Ingraham, Abstr. Annu. Meet. Am. Soc. Microbiol. 1975, K169, p. 175) have shown constitutive synthesis of carbamyl phosphate synthetase in the argR mutant, the regulation of the synthesis of the last five enzymes of the pyrimidine pathway was unaffected. However, in pyrH mutants, known to exhibit derepressed synthesis of the pyrimidine enzymes, a 10-fold derepression of ornithine transcarbamylase was observed.