Growth of on D-glucono-Δ-lactone (Δgl) was found to be associated with a specific coordinate induction of the synthesis of two enzymes of the oxidative pentose phosphate pathway – 6-phosphogluconate dehydrogenase and 6-phosphogluconolactonase – together with that of a third enzyme, gluconokinase. The mutation, responsible for an approximately 80% loss of 6-phosphogluconate dehydrogenase activity and the inability of the cells to grow on Δgl, completely abolished the induction of all three enzymes, while the mutation affected this only partially. One class of revertants, selected for growth on Δgl, was found to have recovered normal dehydrogenase activity and the ability to synthesize the three enzymes when induced by Δgl. Another class of Δgl-positive revertants possessed constitutively elevated levels of gluconokinase. In contrast, glucose-positive revertants of , with restored constitutive dehydrogenase activity, continued to remain deficient in induction of the three enzymes and also failed to grow on Δgl. Induction of 6-phosphogluconate dehydrogenase activity was associated with increased transcription of the gene coding for the major isoenzyme; the transcript remained undetectable in the mutant. Induction of these specific enzymes thus appears to be essential for growth of on Δgl.


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