Proteins are manufactured by ribosomes—macromolecular complexes of protein and RNA molecules that are assembled within major nuclear compartments called nucleoli 1 , 2 . Existing models suggest that RNA polymerases I and III (Pol I and Pol III) are the only enzymes that directly mediate the expression of the ribosomal RNA (rRNA) components of ribosomes. Here we show, however, that RNA polymerase II (Pol II) inside human nucleoli operates near genes encoding rRNAs to drive their expression. Pol II, assisted by the neurodegeneration-associated enzyme senataxin, generates a shield comprising triplex nucleic acid structures known as R-loops at intergenic spacers flanking nucleolar rRNA genes. The shield prevents Pol I from producing sense intergenic noncoding RNAs (sincRNAs) that can disrupt nucleolar organization and rRNA expression. These disruptive sincRNAs can be unleashed by Pol II inhibition, senataxin loss, Ewing sarcoma or locus-associated R-loop repression through an experimental system involving the proteins RNaseH1, eGFP and dCas9 (which we refer to as ‘red laser’). We reveal a nucleolar Pol-II-dependent mechanism that drives ribosome biogenesis, identify disease-associated disruption of nucleoli by noncoding RNAs, and establish locus-targeted R-loop modulation. Our findings revise theories of labour division between the major RNA polymerases, and identify nucleolar Pol II as a major factor in protein synthesis and nuclear organization, with potential implications for health and disease. RNA polymerase II has an unexpected function in the nucleolus, helping to drive the expression of ribosomal RNA and to protect nucleolar structure through a mechanism involving triplex R-loop structures.

中文翻译：

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核仁 RNA 聚合酶 II 驱动核糖体生物合成


蛋白质由核糖体制造，核糖体是蛋白质和 RNA 分子的大分子复合物，在称为核仁 1 , 2 的主要核区室中组装。现有模型表明，RNA 聚合酶 I 和 III（Pol I 和 Pol III）是唯一直接介导核糖体核糖体 RNA (rRNA) 成分表达的酶。然而，我们在这里展示了人类核仁内的 RNA 聚合酶 II (Pol II) 在编码 rRNA 的基因附近运行以驱动其表达。 Pol II 在神经退行性变相关酶 senataxin 的协助下，在核仁 rRNA 基因侧翼的基因间间隔区产生一个包含称为 R 环的三链体核酸结构的屏蔽。该防护罩可防止 Pol I 产生有义基因间非编码 RNA (sincRNA)，从而破坏核仁组织和 rRNA 表达。这些破坏性的sincRNA可以通过涉及蛋白质RNaseH1、eGFP和dCas9（我们称之为“红色激光”）的实验系统通过Pol II抑制、senataxin损失、尤文肉瘤或基因座相关的R环抑制来释放。我们揭示了一种核仁 Pol-II 依赖性机制，该机制可驱动核糖体生物发生，通过非编码 RNA 识别与疾病相关的核仁破坏，并建立针对位点的 R 环调节。我们的研究结果修正了主要 RNA 聚合酶之间的分工理论，并将核仁 Pol II 确定为蛋白质合成和核组织的主要因素，对健康和疾病具有潜在影响。 RNA 聚合酶 II 在核仁中具有意想不到的功能，有助于驱动核糖体 RNA 的表达，并通过涉及三链 R 环结构的机制保护核仁结构。