Edinburgh Napier University

  The nucleotide sequence of a 1980‐base‐pair segment of DNA, containing the lpd gene encoding the lipoamide dehydrogenase component (E3) of the pyruvate dehydrogenase complex of Escherichia coli K 12, has been determined by the dideoxy chain‐termination method. The lpd structural gene comprises 1419 base pairs (473 codons, excluding the initiating AUG codon). It is preceded by a good promoter and an excellent ribosome binding site and it ends with a typical rho‐independent terminator sequence. The results confirm that the lpd gene is an independent gene linked to, but not part of, the ace operon that encodes the E1 and E2 components of the pyruvate dehydrogenase complex. The location and transcriptional polarity of the lpd gene relative to the restriction map of the corresponding region of DNA, are completely consistent with previous genetic and post‐infection labelling studies. The composition, Mr (50554 or 51274 if the FAD cofactor is included), aminoterminal sequence and carboxy‐terminal sequence predicted from the nucleotide sequence are in excellent agreement with previous studies on the purified enzyme. The enzyme also exhibits a remarkable degree of sequence homology with peptides of the pig heart enzyme and with other pyridine nucleotide disulphide oxidoreductases whose sequences have been defined: human erythrocyte glutathione reductase and plasmid‐encoded mercuric reductase.