Nucleotide sequence of the pntA and pntB genes encoding the pyridine nucleotide transhydrogenase of Escherichia coli

Abstract

A 3240-base-pair DNA fragment spanning the pyridine nucleotide transhydrogenase (pnt) genes of Escherichia coli has been sequenced. The sequence contains two open-reading frames, pntA and pntB of 1506 and 1386 base pairs, coding for the transhydrogenase alpha and beta subunits, respectively. The coding sequences are preceded by a promoter-like structure and are most likely co-transcribed. Each coding sequence is preceded by a Shine-Dalgarno sequence. The amino-terminal amino acid sequences were determined from the purified alpha and beta subunits of the transhydrogenase. These sequences agree with those predicted from the nucleotide sequences of the pntA and pntB genes. The predicted relative molecular masses of 53906 (alpha) and 48667 (beta) are close to the values obtained by analysis of the subunits by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Several hydrophobic regions large enough to span the cytoplasmic membrane were observed in each subunit. These results indicate that transhydrogenase is an intrinsic membrane protein.