Abstract：
Chromium is a prevalent toxic heavy metal, and chromate [Cr(VI)] exhibits high mutagenicity and carcinogenicity. The presence of the Cr(VI) efflux protein ChrA has been identified in strains exhibiting resistance to Cr(VI). Nevertheless, certain strains of bacteria that are resistant to Cr(VI) lack the presence of ChrB, a known regulatory factor. Here, a PadR family transcriptional repressor, ChrN, has been identified as a regulator in the response of Enterobacter sp. Z1(CCTCC NO: M 2019147) to Cr(VI). The chrN gene is cotranscribed with the chrA gene, and the transcriptional expression of this operon is induced by Cr(VI). The binding capacity of the ChrN protein to Cr(VI) was demonstrated by both the tryptophan fluorescence assay and Ni-NTA purification assay. The interaction between ChrN and the chrAN operon promoter was validated by reporter gene assay and electrophoretic mobility shift assay. Mutation of the conserved histidine residues His14 and His50 resulted in loss of ChrN binding with the promoter of the chrAN operon. This observation implies that these residues are crucial for establishing a DNA-binding site. These findings demonstrate that ChrN functions as a transcriptional repressor, modulating the cellular response of strain Z1 to Cr(VI) exposure.
摘要：
铬是一种常见的有毒重金属，和铬酸盐[Cr（VI）]表现出高的致突变性和致癌性。已在对Cr（VI）表现出抗性的菌株中鉴定出Cr（VI）流出蛋白ChrA的存在。然而，某些对Cr（VI）具有抗性的细菌菌株缺乏ChrB的存在，已知的调节因子。这里,PadR家族转录抑制因子，ChrN,已被确定为肠杆菌反应的调节剂。Z1(CCTCCNO:M2019147)至Cr(VI)。chrN基因与chrA基因共同定义,该操纵子的转录表达由Cr(VI)诱导。色氨酸荧光测定和Ni-NTA纯化测定均证明了ChrN蛋白与Cr（VI）的结合能力。ChrN与chrAN操纵子启动子之间的相互作用通过报告基因测定和电泳迁移率变化测定得到验证。保守组氨酸残基His14和His50的突变导致ChrN与chrAN操纵子启动子的结合丧失。该观察表明这些残基对于建立DNA结合位点至关重要。这些发现表明，ChrN作为转录抑制因子，调节菌株Z1对Cr(VI)暴露的细胞反应。
