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2-Keto-3-deoxy-gluconate (KDG), an intermediate of the hexuronate pathway inEscherichia coli K-12, is utilized as the sole carbon source only in strains derepressed for the specific KDG-uptake system. KDG is metabolized to pyruvate and glyceraldehyde-3-phosphate via the inducible enzymes KDG-kinase and 2-keto-3-deoxy-6-phosphate-gluconate (KDPG) aldolase. However, another inducible pathway, where the KDG is the branch point, has been demonstrated. Genetic studies of the KDG degradative pathway reported in this paper led to the location of KDG kinase-negative and pleiotropic constitutive mutations. ThekdgK locus, presumably the structural gene of the kinase, occurs at min 69 and is co-transducible withxyl . The mutants, simultaneously constitutive for the uptake, kinase, and aldolase, define akdgR locus at min 36 between the co-transducible markerskdgA andoldD . As to the nature of the control exerted by thekdgR product, we have shown the following. (i) Thermosensitive mutants of thekdgR locus are inducible at low temperature but derepressed at 42 C for the three operons—kdgT (transport system),kdgK , andkdgA (KDPG aldolase). (ii) ThekdgR + allele is dominant to thekdgR constitutive allele. (iii) A deletion inkdgA extending into the regulatory gene,kdgR , leads to a constitutive expression of the nondeleted operons—kdgT andkdgK . These properties demonstrate that thekdg regulon is negatively controlled by thekdgR product. It is presumed that differences in operator and in promotor structures could explain the strong decoordination, respectively, in the induction and catabolic repression, of these three enzymes activities.

Genetic Control of the 2-Keto-3-Deoxy- d -Gluconate Metabolism in Escherichia coli K-12: kdg Regulon