Conformational change of DNA bound to transcription factor response to environmental change

[2Fe-2S]转录因子SoxR在大肠杆菌中作为氧化应激的传感器发挥作用。在氧化状态下，转录通过扭曲靶DNA启动子区域来激活，以通过RNA聚合酶启动转录，而蛋白质的非活性还原状态保持未表征。通过分别用荧光探针2-氨基嘌呤（2Ap）和吡咯并dC位点特异性地取代启动子寡核苷酸的腺嘌呤和胞嘧啶碱基，直接观察到启动子DNA的氧化还原依赖性构象变化。SoxR-DNA复合物中[2Fe-2S]簇的还原显著减弱了掺入DNA中心部分的2Ap部分的荧光强度。这些结果有力地表明，氧化还原变化引起的区域内的DNA启动子区的中央A-T碱基对的构象变化。

The [2Fe-2S] transcriptional factor SoxR functions as a sensor of oxidative stress in Escherichia coli. In the oxidized state, transcription is activated by distorting the target DNA promoter region to initiate transcription by RNA polymerase, while the inactive reduced state of the protein remains uncharacterized. The redox-dependent conformational change of the promoter DNA was directly observed by site-specifically replacing the adenine and cytosine bases of the promoter oligonucleotide with the fluorescent probes 2-aminopurine (2Ap) and pyrrolo-dC, respectively. Reduction of the [2Fe-2S] cluster in SoxR-DNA complex dramatically weakened the fluorescence intensity of the 2Ap moieties incorporated into the central part of the DNA. These results strongly suggested that the redox change caused a large conformational change within the region confined to the central A-T base pairs in the promoter region of the DNA.