MOLYBDATE-DEPENDENT TRANSCRIPTION OF HYC AND NAR OPERONS OF ESCHERICHIA-COLI REQUIRES MOEA PROTEIN AND MODE-MOLYBDATE

In Escherichia coli, ModE-molybdate, a repressor of modABCD operon (mo lybdate transport), was previously shown to be an additional transcrip tional activator of hyc operon (formate hydrogenlyase) and narGHJI ope ron (respiratory nitrate reductase). However, in a modE mutant, both o perons were expressed at about 50% of the wild-type level in a molybda te-dependent manner. This ModE-independent, molybdate-dependent, expre ssion of hyc, narG and narK operons required MoeA protein. An E. coli modE, moeA double mutant failed to produce formate hydrogenlyase or re spiratory nitrate reductase activity irrespective of the growth medium . Tungstate substituted for molybdate in the activation of transcripti on of hyc and nar operons by ModE could not replace molybdate for MoeA -dependent expression. It is proposed that the MoeA-catalyzed product, an activated form of molybdate, interacts with a transcriptional acti vator/regulator other than ModE and regulates hyc and nar operons. (C) 1998 Federation of European Microbiological Societies. Published by E lsevier Science B.V. All rights reserved.