A UNITARY ACCOUNT OF REPRESSION MECHANISM OF ARGININE BIOSYNTHESIS IN ESCHERICHIA COLI .I. GENETIC EVIDENCE

In Escherichia coli strain B growing in minimal medium, added arginine slightly stimulates, while in strain K it represses formation of the arginine biosynthetic enzymes. Nevertheless, mapping and complementation experiments indicate that the respective regulatory genes, argRB‡ ‡ Abbreviations used: The proposals of Demerec, Adelberg, Clark &Hartman (1966) have been followed insofar as possible and the letter designation for the arginine structural genes has been changed from our previous report (Jaooby & Gorini, 1967) so that the alphabetical order corresponds to the biosynthetic sequence (Maas et al., 1964). Thus argE denotes a mutant unable to synthesize aeetylornithinase, argF (previously argD) a mutant in OTC (ornithine transcarbamylase), a∼@ (previously argE) a mutant in ergininosuccinate synthetese, and argH a mutant in arginino-succinase. argR+ is the regulatory locus for the arginine pathway in strain K and argRB the corresponding locus in strain B which has previously also been designated Rz. arg0, is en operator locus specific for argF. Other abbreviations correspond generally to those of Taylor & Trotter (1967) with the following additions; Can, canavanine; NC, N-methyl-N′-nitro-N-nitroso-guanidine. and argR+, are allelic. Since all argR alleles producing an active repressor, including argRB, are trans-dominant to constitutive mutants of either strain, and since an amber mutant of argRB has been found which is constitutive, the pathway in both strains is under negative control, and the regulatory gene product requires translation for its synthesis. A single amino acid substitution can change B-type control to K-type control since correction of the amber argRB mutant by suI+ restores the argRB phenotype while correction by suIII+ leads to arginine repressibility. It is suggested that arginine, or an arginine derivative, activates the repressor product in both strains, but that the formation or function of the active repressor from the argRB product is reduced at high arginine concentration. The eight structural genes of the arginine pathway are scattered in five regions of the chromosome. A technique has been devised for selecting a mutation which partially relieves repression of argF, one of the unclustered genes. This mutation, which is specific for argF, closely linked, and cis-dominant has been designated argOF for operator mutation. The existence of similar operators for the other arginine genes all interacting with the same argR product but differing in affinity is implied by parallel but non-co-ordinate control of the pathway and by the behavior of an argRB temperature-sensitive mutant in which de-repression as a function of temperature differs depending on the arginine enzyme tested. © 1969.