Use of phi(glp-lac) in studies of respiratory regulation of the Escherichia coli anaerobic sn-glycerol-3-phosphate dehydrogenase genes (glpAB)

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Abstract
Expression of the glpA operon encoding the extrinsic membrane anaerobic sn-glycerol-3-phosphate dehydrogenase complex of Escherichia coli K-12 was studied in five strains carrying independent glpA-lac operon fusions. The location of the fusions was confirmed by transduction. Two of the strains produced an enzymatically active anaerobic sn-glycerol-3-phosphate dehydrogenase that accumulated in the cytoplasmic fraction of the cells. This suggests the loss of a specific membrane anchor subunit encoded by a distal gene, glpB, which was disrupted by the insertion. beta-Galactosidase in all five strains carrying phi(glpA-lac) was highly inducible by glycerol only anaerobically. A mutation in fnr, a pleiotropic activator gene, prevented full induction of the phi(glpA-lac), demonstrating that the Fnr protein is a positive regulator of the primary dehydrogenase as well as of the terminal reductases of anaerobic respiratory chains. Low concentrations of the respiratory poison KCN had a permissive effect on aerobic expression of phi(glpA-lac). Aerobic expression of the hybrid operon was also enhanced in isogenic derivatives of the fusion strains deficient in protoporphyrin biosynthesis (hemA). Thus, heme proteins may play a role in mediating aerobic repression of the anaerobic respiratory chain.

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