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Repression of ß-Galactosidase Synthesis by Glucose in Phosphotransferase Mutants of Escherichia coli

REPRESSION IN THE ABSENCE OF GLUCOSE PHOSPHORYLATION

From the ¹ From the Section on Endocrine Biochemistry and the Section on Diabetes and Intermediary Metabolism, Clinical Endocrinology Branch, National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland 20014

Glucose and -methyl glucoside repress ß-galactosidase synthesis in wild type Escherichia coli and in mutant strains deficient in Enzyme I or in the heat-stable protein of the phosphoenolpyruvate-phosphotransferase system. Although the mutants do not grow on glucose and accumulate only a small amount of -methyl glucoside, they are more sensitive to repression by these compounds than are their parent strains. This repression is presumably due to the lowering of the intracellular concentration of cyclic 3',5'-AMP by glucose and -methyl glucoside, since it can be prevented by addition of the nucleotide. In contrast, a mutant deficient in glucose Enzyme II activity was resistant to repression by glucose and -methyl glucoside. Evidently, the repression of ß-galactosidase synthesis by these sugars does not require phosphorylation by the P-enolpyruvate-phosphotransferase system. It does, however, require the presence of Enzyme II activity for the sugars.

An Enzyme I mutant and a heat-stable protein mutant which did not grow on lactose would grow on lactose in the presence of cyclic 3',5'-AMP or of isopropylthio-ß-d-galactoside. Therefore, an intact P-enolpyruvate-phosphotransferase system is not required for lactose utilization by E. coli.

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