A unitary account of the repression mechanism of arginine biosynthesis in Escherichia coli: II. Application to the physiological evidence

Abstract

Ornithine transcarbamylase formation in Escherichia coli strain B is known to be increased by excess arginine. Partial de-repression, however, occurs by growth in an enriched but arginine-free medium or by arginine-limited growth in a chemostat. Furthermore, at growth temperatures higher than 39 °C excess arginine no longer increases but actually represses enzyme formation in strain B, while temperature does not affect control in a repressible strain like K or in a constitutive mutant from B. These physiological effects are intrinsic to the argR alleles of B and K and not to other strain characteristics and suggest that arginine formation is controlled by repression in both strains B and K, but that a secondary effect of arginine produces apparent induction in strain B. It is postulated that the repressor product of argR B gives rise, depending on the arginine concentration, to forms with different affinities for the operator site.