Production of a Soluble Form of Fumarate Reductase by Multiple Gene Duplication in Escherichia coli K12

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Abstract
Ampicillin-hyper-resistant mutants of E. coli K12 bearing multiple gene duplications in the ampC (.beta.-lactamase) gene region of the chromosome overproduced at least 6 proteins with MW 97,000, 80,000, 72,000, 49,000, 33,000 and 26,500 during anaerobic growth. All but 2 of the proteins (MW 80,000 and 49,000) were also overproduced during aerobic growth. The distribution of the proteins in soluble and particulate cell fractions was investigated. The 33,000-MW and 72,000-MW components were identified as .beta.-lactamase and the amp-linked frdA gene product, fumarate reductase, respectively. Cosedimentation of the 26,500-MW component with the fumarate reductase suggested that the smaller protein could be functionally related to the reductase. The lack of correspondence between the amplified proteins and the products of other amp-linked genes, aspA and mop(groE), indicated that these genes are not included in the repetitive sequence. Fumarate reductase activities were amplified up to 32-fold by the multiple gene duplications. Two forms of fumarate reductase were produced: particulate (membrane-bound) and soluble (cytoplasmic). Production of the soluble form occurred when the binding capacity of the membrane was saturated. Both forms of fumarate reductase were enzymically active, but the soluble form was readily inactivated under assay conditions.