来自德国慕尼黑大学的Patrick Cramer及其同事报告了Pol II–TFIIB复合物在自由状态下和被DNA模板及一个短RNA产物结合状态下的高分辨率晶体结构。这些结构和功能数据使我们对转录启动的机制有一个更全面的了解,也解释了RNA和DNA聚合酶的性质之间的一些根本性差别。

-2013年1月17日《自然》

中文翻译


【题目】起始转录RNA聚合酶II–TFIIB复合物的结构和功能

【译文】普通转录因子(TF) IIB是RNA聚合酶(Pol) II所必需的,并且随着其阅读元件B延伸入Pol II活性中心裂缝。Pol II–TFIIB复合物低分辨率结构表明TFIIB是如何在DNA聚集中发挥功能的,但它们缺乏核酸和一半B阅读元件,使得其他TFIIB功能成为谜团。本研究报道了酿酒酵母中Pol II–TFIIB复合物(分辨率为3.4 Å)以及含有DNA模板和一个6核苷酸的RNA产物的初始转录复合物的晶体结构。该结构揭示了整个B阅读元件和蛋白-核酸的相互作用,这和功能数据一起,使得我们对转录起始有更全面的了解。TFIIB部分闭合聚合酶裂缝以定位DNA并在其解链中发挥辅助作用。B阅读元件不会到达活化位点,但结合DNA模板链上游以辅助起始因子序列识别和定位转录起始位点。TFIIB重排活化位点残基,诱导催化性金属离子B的结合,并刺激起始RNA变构合成。TFIIB接着保护出现的DNA-RNA杂交双链以免发生倾斜,这种倾斜将损害RNA合成。当RNA延长超过6个核苷酸,它将从DNA中分离出来,并通过B阅读元件杂环被定向到它的出口通道。一旦RNA延伸至12-13个核苷酸,它与TFIIB碰撞,触发TFIIB移位以及延伸复合物的形成。类似机制可能是所有细胞转录的基础,因为所有真核和古细菌RNA聚合酶都利用TFIIB样因子,而且细菌起始因子∑具有TFIIB样拓扑结构,并包含将B阅读环组装位置、负荷和功能的杂环区3.2。TFIIB及其相似物可能因此阐明DNA聚合酶和RNA聚合酶的根本不同点:非引物依赖的链起始和模板与产物的分离。

英文原稿


[Title]: Structure and function of the initially transcribing RNA polymerase II–TFIIB complex

[Authors]:Sarah Sainsbury,1 Jürgen Niesser1 & Patrick Cramer1

[Abstract]The general transcription factor (TF) IIB is required for RNA polymerase (Pol) II initiation and extends with its B-reader element into the Pol II active centre cleft. Low-resolution structures of the Pol II–TFIIB complex indicated how TFIIB functions in DNA recruitment, but they lacked nucleic acids and half of the B-reader, leaving other TFIIB functions enigmatic. Here we report crystal structures of the Pol II–TFIIB complex from the yeast Saccharomyces cerevisiae at 3.4 Å resolution and of an initially transcribing complex that additionally contains the DNA template and a 6-nucleotide RNA product. The structures reveal the entire B-reader and protein–nucleic acid interactions, and together with functional data lead to a more complete understanding of transcription initiation. TFIIB partially closes the polymerase cleft to position DNA and assist in its opening. The B-reader does not reach the active site but binds the DNA template strand upstream to assist in the recognition of the initiator sequence and in positioning the transcription start site. TFIIB rearranges active-site residues, induces binding of the catalytic metal ion B, and stimulates initial RNA synthesis allosterically. TFIIB then prevents the emerging DNA–RNA hybrid duplex from tilting, which would impair RNA synthesis. When the RNA grows beyond 6 nucleotides, it is separated from DNA and is directed to its exit tunnel by the B-reader loop. Once the RNA grows to 12–13 nucleotides, it clashes with TFIIB, triggering TFIIB displacement and elongation complex formation. Similar mechanisms may underlie all cellular transcription because all eukaryotic and archaeal RNA polymerases use TFIIB-like factors, and the bacterial initiation factor sigma has TFIIB-like topology and contains the loop region 3.2 that resembles the B-reader loop in location, charge and function. TFIIB and its counterparts may thus account for the two fundamental properties that distinguish RNA from DNA polymerases: primer-independent chain initiation and product separation from the template.

原文地址

http://www.nature.com/nature/journal/v493/n7432/full/nature11715.html

 

 

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