Toledano M B, Kullik I, Trinh F, Baird P T, Schneider T D, Storz G
Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
Cell. 1994 Sep 9;78(5):897-909. doi: 10.1016/s0092-8674(94)90702-1.
The redox-sensitive OxyR protein activates the transcription of antioxidant defense genes in response to oxidative stress and represses its own expression under both oxidizing and reducing conditions. Previous studies showed that OxyR-binding sites are unusually long with limited sequence similarity. Here, we report that oxidized OxyR recognizes a motif comprised of four ATAGnt elements spaced at 10 bp intervals and contacts these elements in four adjacent major grooves on one face of the DNA helix. In contrast, reduced OxyR contacts two pairs of adjacent major grooves separated by one helical turn. The two modes of binding are essential for OxyR to function as both an activator and a repressor in vivo. We propose that specific DNA recognition by an OxyR tetramer is achieved with four contacts of intermediate affinity allowing OxyR to reposition its DNA contacts and target alternate sets of promoters as the cellular redox state is altered.
氧化还原敏感的OxyR蛋白在氧化应激反应中激活抗氧化防御基因的转录，并在氧化和还原条件下抑制其自身表达。先前的研究表明，OxyR结合位点异常长，序列相似性有限。在此，我们报告氧化的OxyR识别由四个间隔10 bp的ATAGnt元件组成的基序，并在DNA螺旋一面的四个相邻大沟中与这些元件接触。相比之下，还原的OxyR接触由一个螺旋圈隔开的两对相邻大沟。这两种结合模式对于OxyR在体内作为激活剂和抑制剂发挥功能至关重要。我们提出，OxyR四聚体通过四个中等亲和力的接触实现特异性DNA识别，从而使OxyR能够随着细胞氧化还原状态的改变重新定位其与DNA的接触并靶向不同的启动子组。
