Carbohydrate Accumulation and Metabolism in Escherichia coli: Characteristics of the Reversions of ctr Mutations

The reversion behavior of pleiotropic carbohydrate mutants, previously designated as ctr, was studied. The mutants revert to complete restoration of the wild-type phenotype, as well as to a spectrum of partial wild-type phenotypes. Lac⁺ reversions were found in the lac region (11 min) and some Mal⁺ reversions occurred at malB (79 min), at a distance from the site of the ctr mutations (46 to 47 min). About one-third of Lac⁺ and Mal⁺ revertants were constitutive for uptake of their respective substrates, and one-third modified for inducibility. The remaining third were not distinguishable from wild type. Induction of a ctr mutation in a lac constitutive strain, either operator or repressor mutant, did not affect lactose metabolism. A polar-like ctr mutant, deficient in both enzyme I and heat-stable protein of the phosphoenolpyruvate-dependent phosphotransferase strain was also described. Partial revertants of ctr were still found to lack enzyme I.