Regulation of the adhE gene, which encodes ethanol dehydrogenase in Escherichia coli

The respiratory control of adhE, which encodes ethanol (alcohol) dehydrogenase in Escherichia coli, was examined at the transcriptional level by using various phi (adhE'-lacZ) adhE+ merodiploid strains. Expression of the adhE'-lacZ operon fusion was increased about eightfold by anaerobic growth. Under anaerobic growth conditions, provision of nitrate lowered the level of expression. Nitrate repression was more severe than aerobic repression. From analyses of various mutants with mutations related to nitrate reduction, nitrate repression appears to result from two effects. (i) When nitrate was present, NarL, the positive regulator of the nar operon, exerted a direct repression on adhE expression, which was demonstrable even aerobically. (ii) The chemical reduction of nitrate exerted an indirect effect by altering the cellular redox potential.