Mapping of insertion mutations in gnd of Escherichia coli with deletions defining the ends of the gene

Abstract

A genetic map was prepared for gnd, the gene of Escherichia coli which encodes the metabolically regulated 6-phosphogluconate dehydrogenase. Direct selection methods were used for the isolation of mutants with deletions that define the respective ends of gnd. These selections depended on the availability of a defective lysogen in which gnd was present on a lambda h80 dgnd his prophage located at the att phi 80 region of the chromosome. Mutants with deletions entering gnd from the his-distal end were selected as Gnd- TonB- mutants. Mutants with his-proximal gnd deletions were selected as Gnd-, temperature-resistant mutants of a specially prepared stable lysogen. Gnd- mutants were also isolated after mutagenesis with bacteriophage Mu cts61, and genetic tests were used to determine which mutants carry a Mu cts61 prophage in gnd. The deletion mutations were mapped against each other and against the insertion mutations through the use of F' merodiploid strains. The insertion mutations mapped at seven distinct sites in gnd; three mapped under the deletions defining the his-proximal portion of the gene and three mapped with the his-distal deletions.