Genetic regulation of nitrogen fixation in rhizobia
Genetic regulation of nitrogen fixation in rhizobia
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DOI：
10.1128/mr.58.3.352-386.1994
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发表时间：
1994-09
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影响因子：
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通讯作者：
H. Fischer
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文献类型：
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作者：
H. Fischer
本文对苜蓿根瘤菌、大豆慢生根瘤菌和茎瘤固氮根瘤菌这三种代表性根瘤菌的固氮调控网络进行了比较。这些细菌中固氮基因（nif和fix基因）的转录主要由低氧条件诱导。低氧感测和该信号到nif和fix基因表达水平的传递涉及至少五种调节蛋白，FixL、FixJ、FixK、NifA和RpoN（sigma 54）。这些蛋白质的特性和它们在物种特异性调控途径的功能进行了描述。氧干扰两种转录激活因子FixJ和NifA的活性。FixJ活性通过同源传感器血红素蛋白FixL的磷酸化-去磷酸化来调节。除了NifA蛋白的氧响应性之外，NifA的合成在转录水平上受氧调节。这种类型的控件包括R中的FixLJ。meliloti和A. caulinodans或由B中的自动调节引起。山茱萸NifA与sigma 54 RNA聚合酶一起激活与nif和fix基因以及不直接参与固氮的其他基因相关的-24/-12型启动子的转录。FixK蛋白构成细菌调节剂的Crp-Fnr家族的亚组。虽然参与的FixLJ和FixK在nifA调节是显着不同的三种根瘤菌在这里讨论，他们构成了一个监管级联，统一控制基因（fixNOQP）的表达编码一个独特的细胞色素氧化酶复合物可能需要在低氧条件下的细菌呼吸。在B。此外，FixLJ-FixK级联还控制硝酸盐呼吸和两种sigma 54蛋白之一的基因。
This review presents a comparison between the complex genetic regulatory networks that control nitrogen fixation in three representative rhizobial species, Rhizobium meliloti, Bradyrhizobium japonicum, and Azorhizobium caulinodans. Transcription of nitrogen fixation genes (nif and fix genes) in these bacteria is induced primarily by low-oxygen conditions. Low-oxygen sensing and transmission of this signal to the level of nif and fix gene expression involve at least five regulatory proteins, FixL, FixJ, FixK, NifA, and RpoN (sigma 54). The characteristic features of these proteins and their functions within species-specific regulatory pathways are described. Oxygen interferes with the activities of two transcriptional activators, FixJ and NifA. FixJ activity is modulated via phosphorylation-dephosphorylation by the cognate sensor hemoprotein FixL. In addition to the oxygen responsiveness of the NifA protein, synthesis of NifA is oxygen regulated at the level of transcription. This type of control includes FixLJ in R. meliloti and FixLJ-FixK in A. caulinodans or is brought about by autoregulation in B. japonicum. NifA, in concert with sigma 54 RNA polymerase, activates transcription from -24/-12-type promoters associated with nif and fix genes and additional genes that are not directly involved in nitrogen fixation. The FixK proteins constitute a subgroup of the Crp-Fnr family of bacterial regulators. Although the involvement of FixLJ and FixK in nifA regulation is remarkably different in the three rhizobial species discussed here, they constitute a regulatory cascade that uniformly controls the expression of genes (fixNOQP) encoding a distinct cytochrome oxidase complex probably required for bacterial respiration under low-oxygen conditions. In B. japonicum, the FixLJ-FixK cascade also controls genes for nitrate respiration and for one of two sigma 54 proteins.