A UNITARY ACCOUNT OF REPRESSION MECHANISM OF ARGININE BIOSYNTHESIS IN ESCHERICHIA COLI .2. APPLICATION TO PHYSIOLOGICAL EVIDENCE

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 argRB gives rise, depending on the arginine concentration, to forms with different affinities for the operator site. © 1969.