SUMMARY: The isolation and properties of a mutant of K12 that is totally unable to take up and utilize gluconate are described. Genetical analysis shows this phenotype to be associated with two lesions. One phenotype, designated GntM, is the result of a mutation in a gene co-transducible with the other, designated GntS, is the result of a mutation in a gene () co-transducible with The GntS-phenotype differs little from that of wild-type cells, but GntM GntS organisms grow on gluconate only after a prolonged lag and form a gluconate uptake system that is strongly repressed by pyruvate. Moreover, such GntM mutants readily give rise to further mutants that form a gluconate uptake system, gluconate kinase and 6-phosphogluconate dehydratase constitutively; in partial diploids, this constitutivity is recessive to the inducible character. It is postulated that the GntM phenotype is due to malfunction of a negative control gene , and that specifies the activity of a gluconate uptake system.


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