Regulation of the Arginine Pathway in Proteus mirabilis

SUMMARY: The action of the first enzyme in the arginine pathway of Proteus mirabilis strain 13 is controlled by feed-back inhibition and the formation of arginine-synthesizing enzymes is influenced by the concentration of the end-product. Concentrations of arginine below 10 μg./ml. induce their formation, but higher concentrations result in repression. The variations in enzyme synthesis caused by changes in the arginine content of the medium are markedly smaller than those observed in Escherichia coli. The carbon source affects the response of enzyme synthesis to arginine. Two mutants argR-1 and argR-2 which excrete arginine have higher enzyme levels than the wild type. In one of these the enzymes are repressible and in the other mutant the enzymes are de-repressed. The sites of these two mutants map closely in a locus argR which is linked to a his marker but not to any of the structural arginine genes. The de-repression of enzyme synthesis in these mutants is limited and less than in argR mutants of E. coli. The derepressed state of argR-2 gives it a growth advantage over the wild type if arginine is withdrawn. The derepressed mutants also exhibit a changed response to feedback inhibition.