A gene encoding the TetR-type transcriptional regulator mfsR is located immediately downstream of mfsQ and is transcribed in the same transcriptional unit. mfsQ encodes a major facilitator superfamily (MFS) efflux transporter contributing to the resistance of Stenotrophomonas maltophilia towards disinfectants belonging to quaternary ammonium compounds (QACs), which include benzalkonium chloride (BAC). Phylogenetic analysis revealed that MfsR is closely related to CgmR, a QAC-responsive transcriptional regulator belonging to the TetR family. MfsR regulated the expression of the mfsQR operon in a QAC-inducible manner. The constitutively high transcript level of mfsQ in an mfsR mutant indicated that MfsR functions as a transcriptional repressor of the mfsQR operon. Electrophoretic mobility shift assays showed that purified MfsR specifically bound to the putative promoter region of mfsQR, and in vitro treatments with QACs led to the release of MfsR from binding complexes. DNase I protection assays revealed that the MfsR binding box comprises inverted palindromic sequences located between motifs −35 and −10 of the putative mfsQR promoter. BAC-induced adaptive protection was abolished in the mfsR mutant and was restored in the complemented mutant. Overall, MfsR is a QACs-sensing regulator that controls the expression of mfsQ. In the absence of QACs, MfsR binds to the box located in the mfsQR promoter and represses its transcription. The presence of QACs derepresses MfsR activity, allowing RNA polymerase binding and transcription of mfsQR. This MfsR-MsfQ system enables S. maltophilia to withstand high levels of QACs.

中文翻译：

---

MfsR 是一种 TetR 型转录调节因子，通过调节 mfsQ 在嗜麦芽窄食单胞菌对苯扎氯铵的适应性保护中的作用

编码 TetR 型转录调节因子mfsR 的基因位于mfsQ 的下游，并在同一转录单位中转录。mfsQ编码一个主要的促进剂超家族 (MFS) 外排转运蛋白，有助于嗜麦芽窄食单胞菌对属于季铵化合物 (QAC) 的消毒剂的抗性，其中包括苯扎氯铵 (BAC)。系统发育分析表明，MfsR 与 CgmR 密切相关，CgmR 是属于 TetR 家族的 QAC 响应性转录调节因子。MfsR以 QAC 诱导的方式调节mfsQR操纵子的表达。的组成高转录水平mfsQ在mfsR突变体表明 MfsR 作为mfsQR操纵子的转录阻遏物起作用。电泳迁移率变动分析表明，纯化MFSR特异性结合的推定的启动子区域mfsQR，并在体外用的QAC处理导致MFSR从结合复合物的释放。DNase I 保护分析显示 MfsR 结合盒包含位于推定mfsQR启动子的基序 -35 和 -10 之间的反向回文序列。BAC 诱导的适应性保护在mfsR突变体中被废除，并在补充突变体中恢复。总体而言，MfsR 是一种 QAC 感应调节器，可控制mfsQ的表达. 在没有 QAC 的情况下，MfsR 与位于mfsQR启动子中的框结合并抑制其转录。QAC 的存在解除了 MfsR 的活性，允许 RNA 聚合酶结合和mfsQR 的转录。这种 MfsR-MsfQ 系统使嗜麦芽窄食单胞菌能够承受高水平的 QAC。