RESUMO
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.
Assuntos
Proteínas de Bactérias/fisiologia , Nitrogênio/metabolismo , Fosfoproteínas Fosfatases/fisiologia , Proteínas Quinases/fisiologia , Rhodobacter capsulatus/genética , Transativadores/fisiologia , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Sequência de Bases , Dados de Sequência Molecular , Fosfoproteínas Fosfatases/genética , Fosfoproteínas Fosfatases/metabolismo , Proteínas Quinases/genética , Proteínas Quinases/metabolismo , Rhodobacter capsulatus/crescimento & desenvolvimento , Rhodobacter capsulatus/metabolismo , Análise de Sequência de DNA , Transdução de Sinais , Transativadores/genética , Transativadores/metabolismo , Ureia/metabolismoRESUMO
The Rhodobacter capsulatus nrfA gene product exhibits extensive similarity to the nif (nitrogen fixation) regulatory factor NrfA of Azorhizobium caulinodans and the nucleoid-associated protein Hfq of Escherichia coli. Mutational analysis revealed that, in contrast to the situation in A. caulinodans, NrfA is not essential for diazotrophic growth of R. capsulatus, but it is required for maximal growth rates with N(2) as sole nitrogen source via either molybdenum nitrogenase or the alternative nitrogenase. NrfA was shown to control N(2) fixation in R. capsulatus at the level of expression of the regulatory genes nifA1, nifA2 and anfA, encoding the transcriptional activators of all the other nitrogen fixation genes.
