Transcription analysis of the sucAB, aceEF and lpd genes of Escherichia coli.

Transcript mapping of the Escherichia coli sucAB, aceEF and lpd genes, encoding the five components of the pyruvate and 2-oxoglutarate dehydrogenase complexes, was carried out using single-stranded M13 probes. The sucA and aceE genes encode the specific dehydrogenase components (E1o, E1p), and the sucB and aceF genes encode the specific dihydrolipoamide acyltransferases (E2o, E2p). The common lipoamide dehydrogenase (E3) component is encoded by a single lpd gene adjacent to the aceEF genes. The sucAB, aceEF and lpd genes were all expressed on independent transcripts, and the promoters and terminators were identified. In addition, readthrough transcription from the sucAB genes to a downstream gene designated sucC, and from the aceEF genes to the adjacent lpd gene, was found. The relative levels of transcription of the suc, ace and lpd genes, and of the three different transcript types covering the ace-lpd region, were quantified using RNA from cells grown on different substrates. Most of the E3 components supplying the pyruvate dehydrogenase complex appear to be synthesised from approximately 6415-base aceEF-lpd readthrough transcripts, but additional approximately 4640-base aceEF transcripts terminating after the aceF gene provide a transcriptional basis for the observed stoichiometric excess of E1p and E2p relative to E3 in the assembled complex. Conversely most of the E3 components required for the 2-oxo-glutarate dehydrogenase complex appear to be synthesised from the independent 1670-base lpd transcripts.