Co-regulation of lipoamide dehydrogenase and 2-oxoglutarate dehydrogenase synthesis in Escherichia coli: characterisation of an ArcA binding site in the lpd promoter

The lipoamide dehydrogenase gene (lpdA) encoding the E3 subunits of both th e pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase complexes of Esch erichia coil, is expressed from the upstream pdh and internal lpd promoters of the pdh operon (pdhR-aceEF-lpdA). Under aerobic conditions, the specifi c components of the 2-oxoglutarate dehydrogenase complex encoded by the suc AB genes in the sdhCDAB-sucABCD operon are expressed from the sdh promoter. The provision of lipoamide dehydrogenase subunits for assembly into the 2- oxoglutarate dehydrogenase complex could thus be controlled by co-regulatio n of the lpd promoter with the sdh promoter. Here, the transcription start point of the lpd promoter was defined by primer extension analysis, and an ArcA binding site, TGTTAACAAT, overlapping the lpd promoter and matching th e consensus at 8 out of 10 positions, was identified by in vitro footprint analysis. PdhR was not bound to the lpd promoter nor was ArcA bound specifi cally to the pdh promoter. These results support the view that co-regulatio n of the lpd and sdh promoters is mediated primarily by ArcA. (C) 1998 Fede ration of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.