Hybrid plasmids containing the citrate synthase gene (gltA) of Escherichia coli K12

The Clarke-Carbon colony bank containing ColE1-Escherichia coli hybrid plasmids was screened by conjugation for complementation of the citrate synthase lesion of a gltA mutant. Three ColE1-gltA+ plasmids were identified: pLC26-17 (16.3 kilobase pairs), pLC27-18 (16.35 kb) and pLC31-28 (26.0 kb). The citrate synthase activities of strains containing the hybrid plasmids were amplified 3- to 10-fold. Genetic studies indicated that the smaller plasmids may contain at least part of the succinate dehydrogenase gene (sdh). A physical map of a 19.4 kb region of the E. coli chromosome containing the citrate synthase gene (gltA) was constructed by restriction analysis with the isolated plasmids. The relative positions of 20 restriction sites were defined and a region (3.1 kb) containing the gltA+ gene was identified in the segment common to all three plasmids.