Cross-talk towards the response regulator NtrC controlling nitrogen metabolism in Rhodobacter capsulatus.

Rhodobacter capsulatus NtrB/NtrC two-component regulatory system controls expression of genes involved in nitrogen metabolism including urease and nitrogen fixation genes. The ntrY-ntrX genes, which are located immediately downstream of the nifR3-ntrB-ntrC operon, code for a two-component system of unknown function. Transcription of ntrY starts within the ntrC-ntrY intergenic region as shown by primer extension analysis, but maximal transcription requires, in addition, the promoter of the nifR3-ntrB-ntrC operon. While ntrB and ntrY single mutant strains were able to grow with either urea or N2 as sole nitrogen source, a ntrB/ntrY double mutant (like a ntrC-deficient strain) was no longer able to use urea or N2. These findings suggest that the histidine kinases NtrB and NtrY can substitute for each other as phosphodonors towards the response regulator NtrC.