A novel NO‐responding regulator controls the reduction of nitric oxide in Ralstonia eutropha

• Published in: Molecular microbiology 2000-11, Vol.38 (3), p.626-638
• Main Authors: Pohlmann, Anne, Cramm, Rainer, Schmelz, Karin, Friedrich, Bärbel
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Cupriavidus necator - genetics; Cupriavidus necator - growth & development; Cupriavidus necator - metabolism; DNA-Binding Proteins; DNA-Directed RNA Polymerases - genetics; DNA-Directed RNA Polymerases - metabolism; Gene Expression Regulation, Bacterial - genetics; Genes, Regulator - genetics; Genes, Regulator - physiology; lacZ gene; Molecular Sequence Data; Nitric Oxide - metabolism; nitric-oxide reductase; norA1 gene; norB1 gene; NorR protein; Oxidation-Reduction; Oxidoreductases - chemistry; Oxidoreductases - genetics; Oxidoreductases - metabolism; Physical Chromosome Mapping; Ralstonia eutropha; RNA Polymerase Sigma 54; rpoN gene; Sigma Factor - genetics; Sigma Factor - metabolism; Transcription, Genetic
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1046/j.1365-2958.2000.02157.x

Ralstonia eutropha H16 mediates the reduction of nitric oxide (NO) to nitrous oxide (N2O) with two isofunctional single component membrane‐bound NO reductases (NorB1 and NorB2). This reaction is integrated into the denitrification pathway that involves the successive reduction of nitrate to dinitrogen. The norB1 gene is co‐transcribed with norA1 from a σ54 (RpoN)‐dependent promoter, located upstream of norA1. With the aid of norA1′–lacZ transcriptional fusions and the generation of regulatory mutants, it was shown that norB1 gene transcription requires a functional rpoN gene and the regulator NorR, a novel member of the NtrC family of response regulators. The regulator gene maps adjacent to norAB, is divergently transcribed and present in two copies on the megaplasmid pHG1 (norR1) and the chromosome (norR2). Transcription activation by NorR responds to the availability of NO. A nitrite reductase‐deficient mutant that is incapable of producing NO endogenously, showed a 70% decrease of norA1 expression. Addition of the NO‐donating agent sodium nitroprusside caused induction of norA1′–lacZ transcription. Truncation of the N‐terminal receiver domain of NorR1 interrupted the NO signal transduction and led to a constitutive expression of norA1′–lacZ. The results indicate that NorR controls the reductive conversion of NO in R. eutropha. This reaction is not strictly co‐ordinated on the regulatory level with the other nitrogen oxide‐reducing steps of the denitrification chain that are independent of NorR.