Edinburgh Napier University

  The nucleotide sequence of a 3180‐base‐pair segment of DNA, containing the sucA gene encoding the 2‐oxoglutarate dehydrogenase component (E1o) of the 2‐oxoglutarate dehydrogenase complex of Escherichia coli, has been determined by the dideoxy chain‐termination method. The sucA structural gene contains 2796 base pairs (932 codons, excluding the initiation codon AUG) and encodes a polypeptide having a glutamine residue at the amino terminus, a glutamate residue at the carboxy‐terminus and a calculated Mr= 104905. The predicted amino acid composition is in good agreement with published information obtained by hydrolysis of the purified enzyme. There is a striking lack of sequence homology between the 2‐oxoglutarate dehydrogenase (E1o) and the corresponding pyruvate dehydrogenase (E1p), which suggests that the two components are not closely related in evolutionary terms.

The location and polarity of the sucA gene, relative to the restriction map of the corresponding segment of DNA, are consistent with it being the proximal gene of the suc operon, as defined in previous genetic and post‐infection labelling studies, but it could also form part of a more complex regulatory unit. The sucA gene is preceded by a segment of DNA that contains many substantial regions of hyphenated dyad symmetry including an IS‐like sequence of the type that is thought to function as an intercistronic regulatory element. This segment also contains three putative RNA polymerase binding sites and a good ribosome binding site.