Construction and characterization of a mercury‐independent MerR activator (MerRAC): transcriptional activation in the absence of Hg(II) is accompanied by DNA distortion.
Construction and characterization of a mercury‐independent MerR activator (MerRAC): transcriptional activation in the absence of Hg(II) is accompanied by DNA distortion.
复制标题
DOI：
10.1002/j.1460-2075.1993.tb05673.x
复制
发表时间：
1993-02
期刊：
影响因子：
--
通讯作者：
Julian Parkhill;A. Ansari;Jeffrey G. Wright;N. Brown;T. O’Halloran
中科院分区：
文献类型：
--
作者：
Julian Parkhill;A. Ansari;Jeffrey G. Wright;N. Brown;T. O’Halloran
转座子 Tn501 的 MeR 调节蛋白根据汞离子浓度控制汞抗性 (mer) 基因的表达。 MerR 在迄今为止描述的原核调节蛋白中是独特的，因为它充当 mer 基因转录的阻遏子 [‐Hg(II)] 和激活子 [+Hg(II)]，但在这两种情况下都与 DNA 上的单个位点结合。据推测，这种转录激活过程涉及蛋白质诱导的 DNA 构象变化，使 RNA 聚合酶更容易在启动子处形成开放复合物。 [Frantz and O'Halloran (1990) Biochemistry, 29, 4747–4751] 已经表明，汞存在下 MerR 转录的激活伴随着操作者对化学核酸酶的超敏反应，化学核酸酶对 DNA 结构的局部扭曲敏感。在这里，我们描述了 MerR 中的特定突变，这些突变允许该蛋白在没有变构激活剂 Hg(II) 的情况下刺激转录。我们证明，这些突变体引起的激活程度与 DNA 扭曲程度直接相关，DNA 扭曲程度是通过 MerR-DNA 复合物对核酸酶 Cu-5-苯基-邻菲咯啉的超敏性来测量的。这些结果支持上述模型。
The MeR regulatory protein of transposon Tn501 controls the expression of the mercury resistance (mer) genes in response to the concentration of mercuric ions. MerR is unique among prokaryotic regulatory proteins so far described in that it acts as a repressor [‐Hg(II)] and an activator [+Hg(II)] of transcription of the mer genes, but binds to a single site on the DNA in both cases. This transcriptional activation process has been postulated to involve a protein‐induced conformational change in the DNA that allows RNA polymerase more readily to form an open complex at the promoter. It has been shown [Frantz and O'Halloran (1990) Biochemistry, 29, 4747–4751] that activation of transcription by MerR in the presence of mercury is accompanied by hypersensitivity of the operator to chemical nucleases that are sensitive to local distortion in DNA structure. Here we describe specific mutations in MerR that allow the protein to stimulate transcription in the absence of the allosteric activator Hg(II). We demonstrate that the degree of activation caused by these mutants directly correlates with the degree of DNA distortion as measured by the hypersensitivity of MerR‐DNA complexes to the nuclease Cu‐5‐phenyl‐o‐phenanthroline. These results support the model described above.