6-phosphogluconolactonase mutants of Escherichia coli and a maltose blue gene.

Mutants lacking an enzyme of the oxidative branch of the hexose monophosphate shunt, 6-phosphogluconolactonase (pgl), have been selected as a new class of glucose-negative derivatives of a phosphoglucose isomerase (pgi) mutant. Glucose negativity is not as complete as in mutants lacking phosphoglucose isomerase and glucose-6-phosphate dehydrogenase. Pgi(+), pgl(-) strains have been constructed by transduction and grow almost normally on glucose. Genetic mapping shows that pgl lies between chlD and att-lambda, in the same position as and identical with a blu gene described by Adhya and Schwartz. These blu mutants grown on maltose were recognized by their property to turn blue after treatment with iodine. It is not known how phosphogluconolactonase deficiency causes this reaction; it might be related to accumulation of 6-phosphogluconolactone.