Promoters regulated by the glnG (ntrC) and nifA gene products share a heptameric consensus sequence in the -15 region.

We have determined the nucleotide sequences of the Klebsiella pneumoniae nifL (regulation of N2 fixation genes) and the Escherichia coli glnA (glutamine synthetase) promoters. We compared these sequences with the published sequences of three other promoters that, like the nifL and glnA promoters, are activated by the general nitrogen regulators glnF (ntrA) and glnG (ntrC). The three promoters are the argTr (arginine transport) and dhuA (histidine transport) promoters of Salmonella typhimurium and the nifH (nitrogenase) promoter of Rhizobium meliloti. All five sequences (with at most one mismatch) contain the heptameric consensus sequence T-T-T-T-G-C-A. In the R. meliloti nifH and K. pneumoniae nifL promoters, in which the transcription initiation sites have been determined, the consensus sequence is situated in the -15 region. We recently reported that the K. pneumoniae nifA product, which activates nif genes, can substitute for the glnG (ntrC) product in activating promoters of several genes involved in nitrogen assimilation, including the nifL, the glnA, and the R. meliloti nifH promoters. It is likely that nifA also activates the S. typhimurium argTr and dhuA promoters. In contrast, the glnG product cannot substitute for the nifA product in the activation of the K. pneumoniae nifH (nitrogenase) promoter. Consistent with this latter observation, and supporting the conclusion that the T-T-T-T-G-C-A sequence is a regulatory site for glnG product activation, the K. pneumoniae nifH promoter (C-C-C-T-G-C-A) has only partial similarity with the T-T-T-T-G-C-A consensus sequence in the -15 region.