Structure of RNA polymerase I transcribing ribosomal DNA genes
Structure of RNA polymerase I transcribing ribosomal DNA genes
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DOI：
10.1038/nature20561
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发表时间：
2016-12-22
期刊：
影响因子：
64.8
通讯作者：
Frangakis, Achilleas S.
中科院分区：
文献类型：
--
作者：
Neyer, Simon;Kunz, Michael;Frangakis, Achilleas S.
RNA聚合酶I（Pol I）是转录核糖体DNA（rDNA）并调节真核细胞生长的高度加工性酶（1-4）。来自酵母酿酒酵母的游离Pol I的晶体结构揭示了由“连接器”元件稳定的酶的二聚体和含有处于非活性构象的活性中心的扩展裂缝（5-7）。中央桥螺旋展开和Pol-I特异性的“扩展器”元件占据DNA模板结合位点。Pol I在其活性转录构象中的结构尚未确定，而Pol II和Pol III的结构已经用结合的DNA模板和RNA转录物解决（8-10）。在这里，我们报告的结构，主动转录Pol我从酵母解决了两种不同的冷冻电子显微镜方法。3.8埃分辨率的单颗粒结构揭示了一个收缩的活性中心裂缝与结合的DNA和RNA，和一个狭窄的孔下的活性位点，不再持有RNA切割刺激结构域的亚基A12.2。从转录细胞rDNA的Pol I酶的冷冻电子断层扫描图确定的29埃分辨率的结构证实了裂缝的收缩，并揭示了进入和离开的rDNA围成约150度的角度。该结构表明了一种模型，用于调节转录延伸，其中收缩和扩张的聚合酶构象分别与活性和非活性状态相关。
RNA polymerase I (Pol I) is a highly processive enzyme that transcribes ribosomal DNA (rDNA) and regulates growth of eukaryotic cells(1-4). Crystal structures of free Pol I from the yeast Saccharomyces cerevisiae have revealed dimers of the enzyme stabilized by a 'connector' element and an expanded cleft containing the active centre in an inactive conformation(5-7). The central bridge helix was unfolded and a Pol-I-specific 'expander' element occupied the DNA-template-binding site. The structure of Pol I in its active transcribing conformation has yet to be determined, whereas structures of Pol II and Pol III have been solved with bound DNA template and RNA transcript(8-10). Here we report structures of active transcribing Pol I from yeast solved by two different cryo-electron microscopy approaches. A single-particle structure at 3.8 angstrom resolution reveals a contracted active centre cleft with bound DNA and RNA, and a narrowed pore beneath the active site that no longer holds the RNA-cleavage-stimulating domain of subunit A12.2. A structure at 29 angstrom resolution that was determined from cryo-electron tomograms of Pol I enzymes transcribing cellular rDNA confirms contraction of the cleft and reveals that incoming and exiting rDNA enclose an angle of around 150 degrees. The structures suggest a model for the regulation of transcription elongation in which contracted and expanded polymerase conformations are associated with active and inactive states, respectively.