Location and sequence of the promoter of the gene for the NADH-dependent nitrite reductase of Escherichia coli and its regulation by oxygen, the Fnr protein and nitrite.

The DNA sequence containing the start of the Escherichia coli nirB gene is reported. The N-terminal amino acid sequence of purified NADH-dependent nitrite reductase coincided with that predicted from the DNA sequence, confirming that nirB is the structural gene for nitrite reductase apoprotein and identifying the translation start point. Using nuclease S1 mapping, the sole transcription startpoint for the nirB gene was found 23 or 24 base-pairs upstream from the ATG initiation codon. By subcloning successively smaller DNA fragments into a beta-galactosidase expression vector plasmid, we located the promoter within a sequence bounded by a TaqI site at +14 with respect to the transcription startpoint and a HpaII site at -208. Measurements in vivo of beta-galactosidase expression and RNA levels due to nirB promoter activity showed that this promoter was activated during anaerobic growth. Optimal activity was found only after anaerobic growth in the presence of nitrite. The sequence of the nirB promoter is compared with sequences found at other anaerobically activated promoters.