Methylarsenite [MAs(III)] is a highly toxic arsenical produced by some microbes as an antibiotic. In this study, we demonstrate that a PadR family transcriptional regulator, PadR_ars, from Azospirillum halopraeferens strain Au 4 directly binds to the promoter region of the arsenic resistance (ars) operon (consisting of padR_ars, arsV, and arsW) and represses transcription of arsV and arsW genes involved in MAs(III) resistance. Quantitative reverse transcriptase PCR and transcriptional reporter assays showed that transcription of the ars operon is induced strongly by MAs(III) and less strongly by arsenite and antimonite. Electrophoretic mobility shift assays with recombinant PadR_ars showed that it represses transcription of the ars operon by binding to two inverted-repeat sequences within the ars promoter. PadR_ars has two conserved cysteine pairs, Cys56/57 and Cys133/134; mutation of the first pair to serine abolished the transcriptional response of the ars operon to trivalent metalloids, suggesting that Cys56/57 form a binding site for trivalent metalloids. Either C133S or C134S derivative responses to MAs(III) but not As(III) or Sb(III), suggesting that it is a third ligand to trivalent metalloids. PadR_ars represents a new type of repressor proteins regulating transcription of an ars operon involved in the resistance to trivalent metalloids, especially MAs(III).

中文翻译：

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PadR 家族转录抑制因子控制 Azospirillum halopraeferens 菌株 Au 4 的三价类金属抗性操纵子的转录

甲基亚砷酸盐 [MAs(III)] 是一种剧毒的砷化物，由某些微生物产生，用作抗生素。在这项研究中，我们证明 PadR 家族转录调节因子 PadR _ars来自Azospirillum halopraeferens菌株 Au 4 直接结合砷抗性 ( ars ) 操纵子的启动子区域（由padR _ars、arsV和arsW 组成）并抑制转录参与 MAs(III) 抗性的arsV和arsW基因。定量逆转录酶 PCR 和转录报告基因检测显示ars的转录操纵子由 MAs(III) 强烈诱导，而亚砷酸盐和锑酸盐则不太强烈。_{重组 PadR ars}的电泳迁移率变动分析表明，它通过结合ars启动子内的两个反向重复序列来抑制ars操纵子的转录。PadR _ars有两个保守的半胱氨酸对，Cys56/57 和 Cys133/134；第一对丝氨酸的突变消除了ars操纵子对三价类金属的转录反应，表明 Cys56/57 形成了三价类金属的结合位点。C133S 或 C134S 衍生物对 MAs(III) 有反应，但对 As(III) 或 Sb(III) 没有反应，表明它是三价准金属的第三配体。掌上_电脑代表一种新型的阻遏蛋白，调节ars操纵子的转录，该操纵子参与对三价类金属，尤其是 MAs(III) 的抗性。