Fudan University Shanghai Cancer Center, Institutes of Biomedical Sciences, State Key Laboratory of Genetic Engineering and Shanghai Key Laboratory of Medical Epigenetics, Shanghai Medical College of Fudan University, Shanghai, 200032, China.
The International Co-laboratory of Medical Epigenetics and Metabolism, Ministry of Science and Technology of China, Department of Systems Biology for Medicine, School of Basic Medical Sciences, Shanghai Medical College of Fudan University, Shanghai, 200032, China.
Cell Res. 2021 Jul;31(7):791-800. doi: 10.1038/s41422-021-00472-2. Epub 2021 Mar 5.
RNA polymerase III (Pol III) transcribes essential structured small RNAs, such as tRNAs, 5S rRNA and U6 snRNA. The transcriptional activity of Pol III is tightly controlled and its dysregulation is associated with human diseases, such as cancer. Human Pol III has two isoforms with difference only in one of its subunits RPC7 (α and β). Despite structural studies of yeast Pol III, structure of human Pol III remains unsolved. Here, we determined the structures of 17-subunit human Pol IIIα complex in the backtracked and post-translocation states, respectively. Human Pol III contains a generally conserved catalytic core, similar to that of yeast counterpart, and structurally unique RPC3-RPC6-RPC7 heterotrimer and RPC10. The N-ribbon of TFIIS-like RPC10 docks on the RPC4-RPC5 heterodimer and the C-ribbon inserts into the funnel of Pol III in the backtracked state but is more flexible in the post-translocation state. RPC7 threads through the heterotrimer and bridges the stalk and Pol III core module. The winged helix 1 domain of RPC6 and the N-terminal region of RPC7α stabilize each other and may prevent Maf1-mediated repression of Pol III activity. The C-terminal FeS cluster of RPC6 coordinates a network of interactions that mediate core-heterotrimer contacts and stabilize Pol III. Our structural analysis sheds new light on the molecular mechanism of human Pol IIIα-specific transcriptional regulation and provides explanations for upregulated Pol III activity in RPC7α-dominant cancer cells.
RNA 聚合酶 III（Pol III）转录必需的结构小 RNA，如 tRNA、5S rRNA 和 U6 snRNA。Pol III 的转录活性受到严格控制，其失调与人类疾病有关，如癌症。人类 Pol III 有两种同工酶，仅在其一个亚基 RPC7（α 和 β）上有所不同。尽管对酵母 Pol III 进行了结构研究，但人类 Pol III 的结构仍未解决。在这里，我们分别确定了处于回溯和易位后状态的 17 亚基人 Pol IIIα 复合物的结构。人类 Pol III 包含一个通常保守的催化核心，与酵母对应物相似，并且具有结构独特的 RPC3-RPC6-RPC7 异三聚体和 RPC10。TFIIS 样 RPC10 的 N-ribbon 与 RPC4-RPC5 异二聚体对接，C-ribbon 插入回溯状态下的 Pol III 漏斗中，但在易位后状态下更灵活。RPC7 穿过异三聚体并桥接柄部和 Pol III 核心模块。RPC6 的翼状螺旋 1 结构域和 RPC7α 的 N 端区域相互稳定，可能防止 Maf1 介导的 Pol III 活性抑制。RPC6 的 C 端 FeS 簇协调一个相互作用网络，介导核心-异三聚体接触并稳定 Pol III。我们的结构分析为人类 Pol IIIα 特异性转录调控的分子机制提供了新的见解，并为 RPC7α 主导的癌细胞中 Pol III 活性上调提供了解释。
