Pohlmann A, Cramm R, Schmelz K, Friedrich B
Humboldt-Universität zu Berlin, Chausseestrasse 117, 10115 Berlin, Germany.
Mol Microbiol. 2000 Nov;38(3):626-38. 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 sigma54 (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.
嗜麦芽窄食单胞菌H16通过两种同功能的单组分膜结合型一氧化氮还原酶（NorB1和NorB2）将一氧化氮（NO）还原为一氧化二氮（N₂O）。该反应整合到反硝化途径中，该途径涉及硝酸盐连续还原为氮气。norB1基因与norA1从位于norA1上游的依赖于σ⁵⁴（RpoN）的启动子共转录。借助norA1'-lacZ转录融合以及调控突变体的产生，研究表明norB1基因转录需要功能性的rpoN基因和调控因子NorR，NorR是响应调控因子NtrC家族的一个新成员。调控基因定位于norAB相邻处，呈反向转录，在大质粒pHG1（norR1）和染色体（norR2）上各有两个拷贝。NorR的转录激活对NO的可用性作出响应。一个缺乏亚硝酸还原酶且无法内源性产生NO的突变体，其norA1表达下降了70%。添加供NO的硝普钠会诱导norA1'-lacZ转录。NorR1的N端接收结构域的截短中断了NO信号转导，并导致norA1'-lacZ的组成型表达。结果表明NorR控制嗜麦芽窄食单胞菌中NO的还原转化。该反应在调控水平上与反硝化链中其他独立于NorR的氮氧化物还原步骤没有严格协调。
