NADPH INHIBITS TRANSCRIPTION OF THE ESCHERICHIA-COLI MANGANESE SUPEROXIDE-DISMUTASE GENE (SODA) INVITRO

We have previously reported that the thiols glutathione, dithiothreito l, and beta-mercaptoethanol suppress transcription of the Escherichia coli manganese-containing superoxide dismutase gene (sodA) in an in vi tro coupled transcription plus translation system (Gardner, P. R., and Fridovich, I. (1987) J. Biol. Chem. 262, 17591-17595). We now report that NADPH, but not NADH, selectively decreases transcription of sodA in vitro and that an NADPH generating system utilizing glucose 6-phosp hate and the corresponding dehydrogenase markedly augments this suppre ssive effect. A redox buffer containing various ratios of oxidized and reduced glutathione also modulated transcription of sodA thus demonst rating the existence of a redox-sensitive mechanism controlling sodA t ranscription. Fusion of a 120-base pair fragment, containing 90 base p airs of DNA upstream of the sodA transcription initiation site, to a p romoterless galactokinase gene (galK) conferred redox-sensitivity to G alK synthesis. We propose that these redox effects act through a redox -sensitive regulator of sodA and that the anabolic reduction charge, [ NADPH]/([NADPH] + [NADP+]), is one cellular signal controlling sodA tr anscription.