Regulation of Klebsiella pneumoniae Nitrogen Fixation Gene Promoters by Regulatory Proteins ntrC, nifA, and nifL

Abstract

Klebsiella pneumoniae, a free living enteric bacterium, reduces N2 to NH4 only under conditions of nitrogen starvation and low 02 tension. Its cluster of 17 nitrogen fixation (nif) genes are organized in 8 transcription units near the his operon (Beynon et al, 1983). One operon, nifLA, codes for a repressor and an activator. The nifL product mediates repression under conditions of N-excess and high 02 tension, and the nifA product is required for transcription of all other nif genes (for review, see Roberts, Brill, 1981). Recent findings have shown that the nifA product has the capacity to activate promoters of the central nitrogen regulatory (NTR) system (Ow, Ausubel, 1983; Merrick, 1983). Whether nifA-mediated activation of NTR pathways is physiologically and evolutionarily significant is not clear. But in light of a possible contribution by nifA in activating NTR genes, the following model was proposed (Ow, Ausubel, 1983).KeywordsFixed NitrogenGlutamine SynthetaseNitrogen StarvationPromoter MutantPromoter StrengthThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.