Department of Biomedical Research, National Jewish Health, Denver, United States.
Department of Immunology and Microbiology, School of Medicine, University of Colorado, Aurora, United States.
Elife. 2020 Feb 12;9:e53930. doi: 10.7554/eLife.53930.
More than 30% of genes in higher eukaryotes are regulated by promoter-proximal pausing of RNA polymerase II (Pol II). Phosphorylation of Pol II CTD by positive transcription elongation factor b (P-TEFb) is a necessary precursor event that enables productive transcription elongation. The exact mechanism on how the sequestered P-TEFb is released from the 7SK snRNP complex and recruited to Pol II CTD remains unknown. In this report, we utilize mouse and human models to reveal methylphosphate capping enzyme (MePCE), a core component of the 7SK snRNP complex, as the cognate substrate for Jumonji domain-containing 6 (JMJD6)'s novel proteolytic function. Our evidences consist of a crystal structure of JMJD6 bound to methyl-arginine, enzymatic assays of JMJD6 cleaving MePCE in vivo and in vitro, binding assays, and downstream effects of knockout and overexpression on Pol II CTD phosphorylation. We propose that JMJD6 assists bromodomain containing 4 (BRD4) to recruit P-TEFb to Pol II CTD by disrupting the 7SK snRNP complex.
高等真核生物中超过 30%的基因受 RNA 聚合酶 II（Pol II）启动子近端暂停的调控。Pol II CTD 的磷酸化是一个必要的前体事件，可实现有效的转录延伸。目前尚不清楚被隔离的 P-TEFb 是如何从 7SK snRNP 复合物中释放出来并募集到 Pol II CTD 的。在本报告中，我们利用小鼠和人类模型揭示了甲基磷酸帽酶（MePCE）作为包含 Jumonji 结构域的 6 型（JMJD6）新型蛋白水解功能的靶标，它是 7SK snRNP 复合物的核心组成部分。我们的证据包括 JMJD6 与甲基精氨酸结合的晶体结构、JMJD6 在体内和体外切割 MePCE 的酶促测定、结合测定以及 JMJD6 缺失和过表达对 Pol II CTD 磷酸化的下游影响。我们提出，JMJD6 通过破坏 7SK snRNP 复合物来协助溴结构域蛋白 4（BRD4）将 P-TEFb 募集到 Pol II CTD。
