Department of Molecular Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
Science. 2021 Jan 15;371(6526):305-309. doi: 10.1126/science.abf1870.
To initiate cotranscriptional splicing, RNA polymerase II (Pol II) recruits the U1 small nuclear ribonucleoprotein particle (U1 snRNP) to nascent precursor messenger RNA (pre-mRNA). Here, we report the cryo-electron microscopy structure of a mammalian transcribing Pol II-U1 snRNP complex. The structure reveals that Pol II and U1 snRNP interact directly. This interaction positions the pre-mRNA 5' splice site near the RNA exit site of Pol II. Extension of pre-mRNA retains the 5' splice site, leading to the formation of a "growing intron loop." Loop formation may facilitate scanning of nascent pre-mRNA for the 3' splice site, functional pairing of distant intron ends, and prespliceosome assembly. Our results provide a starting point for a mechanistic analysis of cotranscriptional spliceosome assembly and the biogenesis of mRNA isoforms by alternative splicing.
为了启动共转录剪接，RNA 聚合酶 II（Pol II）招募 U1 小核核糖核蛋白颗粒（U1 snRNP）到新生前体信使 RNA（pre-mRNA）。在这里，我们报告了哺乳动物转录 Pol II-U1 snRNP 复合物的冷冻电子显微镜结构。该结构显示 Pol II 和 U1 snRNP 直接相互作用。这种相互作用将 pre-mRNA 的 5' 剪接位点定位在 Pol II 的 RNA 出口附近。pre-mRNA 的延伸保留了 5' 剪接位点，导致形成“生长的内含子环”。环的形成可能有助于新生 pre-mRNA 扫描 3' 剪接位点、远距离内含子末端的功能配对以及前剪接体的组装。我们的结果为共转录剪接体组装和通过选择性剪接生成 mRNA 异构体的机制分析提供了一个起点。
