Involvement of the ntrA gene product in the anaerobic metabolism of Escherichia coli.

The ntr A gene product, required for expression of genes involved in nitrogen fixation (nif) and regulation (ntr), was shown to be necessary for the expression of the two enzymes of the anaerobically inducible formate hydrogenlyase (FHL) pathway, formate dehydrogenase (FDHH) and hydrogenase isoenzyme 3. Consistent with this finding, the gene encoding the selenopolypeptide (fdhF) of FDHH was shown to have a nif consensus promoter. The levels of six other anaerobically inducible enzymes were examined and found to be ntrA independent. Significantly, these latter six enzymes are dependent upon the fnr gene product for their expression while FDHH and hydrogenase 3 are fnr independent. These findings indicate that there are at least two classes of anaerobically regulated promoters: one class which is ntrA dependent and fnr independent and a second class which is fnr dependent and ntr A independent.