Department of Molecular Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
Department of Molecular Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
Cell. 2017 Mar 23;169(1):120-131.e22. doi: 10.1016/j.cell.2017.03.003.
Transcription initiation at the ribosomal RNA promoter requires RNA polymerase (Pol) I and the initiation factors Rrn3 and core factor (CF). Here, we combine X-ray crystallography and cryo-electron microscopy (cryo-EM) to obtain a molecular model for basal Pol I initiation. The three-subunit CF binds upstream promoter DNA, docks to the Pol I-Rrn3 complex, and loads DNA into the expanded active center cleft of the polymerase. DNA unwinding between the Pol I protrusion and clamp domains enables cleft contraction, resulting in an active Pol I conformation and RNA synthesis. Comparison with the Pol II system suggests that promoter specificity relies on a distinct "bendability" and "meltability" of the promoter sequence that enables contacts between initiation factors, DNA, and polymerase.
转录起始于核糖体 RNA 启动子需要 RNA 聚合酶（Pol）I 和起始因子 Rrn3 和核心因子（CF）。在这里，我们结合 X 射线晶体学和 cryo-electron microscopy（cryo-EM）获得了基本 Pol I 起始的分子模型。三亚基 CF 结合上游启动子 DNA，对接至 Pol I-Rrn3 复合物，并将 DNA 加载到聚合酶的扩展活性中心裂口中。Pol I 突出和夹钳结构域之间的 DNA 解旋使裂口收缩，导致 Pol I 构象和 RNA 合成的活性化。与 Pol II 系统的比较表明，启动子特异性依赖于启动子序列的独特的“弯曲度”和“融化度”，从而使起始因子、DNA 和聚合酶之间能够发生接触。
