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首页> 外文期刊>Journal of bacteriology >Role of Escherichia coli Nitrogen Regulatory Genes in the Nitrogen Response of the Azotobacter vinelandiiNifL-NifA Complex
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Role of Escherichia coli Nitrogen Regulatory Genes in the Nitrogen Response of the Azotobacter vinelandiiNifL-NifA Complex

机译：大肠杆菌氮调控基因在葡萄固氮菌NifL-NifA复合物氮响应中的作用

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The redox-sensing flavoprotein NifL inhibits the activity of the nitrogen fixation (nif)-specific transcriptional activator NifA in Azotobacter vinelandii in response to molecular oxygen and fixed nitrogen. Although the mechanism whereby the A. vinelandii NifL-NifA system responds to fixed nitrogen in vivo is unknown, the glnK gene, which encodes a PII-like signal transduction protein, has been implicated in nitrogen control. However, the precise function of A. vinelandii glnK in this response is difficult to establish because of the essential nature of this gene. We have shown previously that A. vinelandii NifL is able to respond to fixed nitrogen to control NifA activity when expressed inEscherichia coli. In this study, we investigated the role of the E. coli PII-like signal transduction proteins in nitrogen control of the A. vinelandii NifL-NifA regulatory system in vivo. In contrast to recent findings with Klebsiella pneumoniae NifL, our results indicate that neither the E. coli PII nor GlnK protein is required to relieve inhibition byA. vinelandii NifL under nitrogen-limiting conditions. Moreover, disruption of both the E. coli glnB andntrC genes resulted in a complete loss of nitrogen regulation of NifA activity by NifL. We observe that glnB ntrC and glnB glnK ntrC mutant strains accumulate high levels of intracellular 2-oxoglutarate under conditions of nitrogen excess. These findings are in accord with our recent in vitro observations (R. Little, F. Reyes-Ramirez, Y. Zhang, W. Van Heeswijk, and R. Dixon, EMBO J. 19:6041–6050, 2000) and suggest a model in which nitrogen control of the A. vinelandii NifL-NifA system is achieved through the response to the level of 2-oxoglutarate and an interaction with PII-like proteins under conditions of nitrogen excess.
机译：氧化还原敏感的黄素蛋白NifL响应分子氧和固氮，抑制 Azotobacter vinelandii 中氮固定（ nif ）特异性转录激活因子NifA的活性。虽然是 A的机制。体内NifL-NifA系统对固定氮的反应尚不清楚， glnK 基因编码PII样信号转导蛋白，已被证明与氮的控制有关。但是， A的精确功能。 vinelandii glnK 在这种反应中很难建立，因为该基因的本质。前面我们已经显示了 A。当在大肠杆菌中表达时，vinelandii NifL能够响应固定氮，从而控制NifA活性。在这项研究中，我们调查了 E的作用。大肠杆菌 PII样信号转导蛋白对 A的氮控制。体内的NifL-NifA调节系统。与最近发现的肺炎克雷伯菌 NifL相反，我们的结果表明 E都没有。大肠杆菌 PII或GlnK蛋白是缓解 A抑制作用所必需的。氮限制条件下的藤本植物NifL。而且，这两个 E都被破坏了。大肠杆菌glnB 和 ntrC 基因导致NifL完全丧失了对NifA活性的氮调节作用。我们观察到 glnB ntrC 和 glnB glnK ntrC 突变株在氮过量的条件下会积聚高水平的细胞内2-氧戊二酸。这些发现与我们最近的体外观察结果一致（R. Little，F. Reyes-Ramirez，Y. Zhang，W. Van Heeswijk，和R. Dixon，EMBO J. 19：6041-6050，2000），并建议模型中的 A进行氮控制。通过对2-氧戊二酸水平的响应以及在氮过量条件下与PII样蛋白的相互作用来实现NifL-NifA系统。

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