Cloning, mapping, and expression of the fumarase gene of Escherichia coli K-12

Abstract

Two classes of fumarase-transducing phages, .lambda. fumA and .lambda. fumB, were isolated from populations of recombinant phages containing HindIII fragments of E. coli DNA; they were isolated by virtue of their ability to complement the metabolic lesion of a fumarase-negative mutant. The strongly complementing .lambda. fumA phages contained a 6.2-kilobase HindIII fragment encoding the following: the fumA gene, located at 35.5 min in the E. coli linkage map and expressing the major fumarase activity; the mannosephosphate isomerase gene, manA; and an unidentified gene, g48. The 3 genes were located relative to the restriction map of the cloned fragment and the genetic linkage map (terC-g48-fumA-manA-uidAoR), their transcription polarities were defined as anticlockwise in the chromosome, and the MW of the corresponding gene products were established: fumA, 61,500; manA, 42,000; g48, 48,000. Organisms containing the fumA gene subcloned in multicopy plasmids overproduced fumarase up to 50-fold. The weakly complementing class of transducing phages, .lambda. fumB, contained several genes in an 8.2-kilobase HindIII fragment, including one (fumB) that determines a minor fumarase activity. Complementation by fumB was only observed in high-copy situations such as transduction plaques and in strains containing a multicopy plasmid in which 40% of normal fumarase activity was detected. The basis for the complementation by fumB was not defined.