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首页> 外文期刊>Applied Microbiology >NasT-Mediated Antitermination Plays an Essential Role in the Regulation of the Assimilatory Nitrate Reductase Operon in Azotobacter vinelandii
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NasT-Mediated Antitermination Plays an Essential Role in the Regulation of the Assimilatory Nitrate Reductase Operon in Azotobacter vinelandii

机译：NasT介导的抗终止作用在葡萄固氮菌中硝酸盐还原酶操纵子的调控中起重要作用。

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Azotobacter vinelandii is a well-studied model system for nitrogen fixation in bacteria. Regulation of nitrogen fixation in A. vinelandii is independent of NtrB/NtrC, a conserved nitrogen regulatory system in proteobacteria. Previous work showed that an ntrC mutation in A. vinelandii resulted in a loss of induction of assimilatory nitrate and nitrite reductases encoded by the nasAB operon. In addition to NtrC, several other proteins, including NasT, a protein containing a potential RNA-binding domain ANTAR (AmiR and NasR transcription antitermination regulators), have been implicated in nasAB regulation. In this work, we characterize the sequence upstream of nasA and identify several DNA sequence elements, including two potential NtrC binding sites and a putative intrinsic transcriptional terminator upstream of nasA that are potentially involved in nasAB regulation. Our analyses confirm that the nasAB promoter, P _(nasA), is under NtrC control. However, unlike NtrC-regulated promoters in enteric bacteria, P _(nasA) shows high activity in the presence of ammonium; in addition, the P _(nasA) activity is altered in the nifA gene mutation background. We discuss the implication of these results on NtrC-mediated regulation in A. vinelandii . Our study provides direct evidence that induction of nasAB is regulated by NasT-mediated antitermination, which occurs within the leader region of the operon. The results also support the hypothesis that NasT binds the promoter proximal hairpin of nasAB for its regulatory function, which contributes to the understanding of the regulatory mechanism of ANTAR-containing antiterminators.
机译：葡萄固氮菌是研究良好的细菌固氮模型系统。葡萄曲霉中固氮的调控独立于NtrB / NtrC，这是蛋白细菌中保守的氮调控系统。先前的工作表明，A。vinelandii中的ntrC突变导致nasAB操纵子编码的同化硝酸盐和亚硝酸盐还原酶的诱导作用丧失。除NtrC外，其他几种蛋白质，包括NasT（一种含有潜在RNA结合域ANTAR（AmiR和NasR转录抗终止调节剂）的蛋白质）也涉及nasAB调控。在这项工作中，我们表征了nasA上游的序列，并鉴定了几种DNA序列元件，包括两个潜在的NtrC结合位点和nasA上游可能涉及nasAB调节的推定的固有转录终止子。我们的分析证实，nasAB启动子P_（nasA）受NtrC控制。但是，与肠细菌中NtrC调节的启动子不同，P_（nasA）在铵存在下显示出高活性;另外，在nifA基因突变背景中P_（nasA）活性被改变。我们讨论了这些结果对Atr vinelandii中NtrC介导的调控的影响。我们的研究提供直接证据，表明nasAB的诱导受NasT介导的抗终止作用的调节，该作用发生在操纵子的前导区内。结果还支持以下假设：NasT结合nasAB的启动子近端发夹的调节功能，这有助于理解含ANTAR的抗终止剂的调节机制。

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