Structural understanding of 7SK-snRNP mediated transcriptional regulation

摘要 在许多细胞和病毒mRNA的转录过程中，RNA聚合酶II被抑制， 负延伸因子，并需要正延伸因子pTEFb来释放它 停滞状态。7SK小核RNA与HEXIM衔接蛋白的结合作为一部分， 的7SK小核核糖核蛋白（7SK snRNP）复合物通常保持pTEFb 隔离在核内，这种相互作用必须被克服， 转录延伸研究得最多的调节机制的例子是， 转录延伸的基础是HIV达特系统。简单地说，为了释放停滞的 在其转录物的一种状态下，HIV已经进化出病毒达特蛋白，该蛋白结合7 SK并取代 HEXIM劫持pTEFb。另一方面，一些细胞因子，如BRD4，也能达到同样的效果。 结果没有取代HEXIM。本建议旨在获得一个机械的理解， 呈现给所有转录调节子的结构状态遇到HEXIM驱动的 抑制性7SK snRNP复合物，以及如何捕获pTEFb是由专门的HIV 达特转录因子。目标是：（1）了解基本机制是否 保持在HEXIM 1和2中，如果不同的正转录调节因子利用HEXIM 1和2， 机制，（#2）以确定存在于7SK中的单个RNA结构域的结构。 snRNA和（#3）来解析HEXIM结合的复合物和Tat结合的复合物的结构。

Abstract During transcription of many cellular and viral mRNAs, RNA Polymerase II is inhibited by negative elongation factors and requires the positive elongation factor, pTEFb, to release this stalled state. The binding of the 7SK small nuclear RNA to the HEXIM adapter protein as a part of the 7SK small nuclear ribonucleoprotein (7SK snRNP) complex normally keeps pTEFb sequestered within the nucleus and this interaction must be overcome for productive transcriptional elongation. The most well-studied example of the regulatory mechanisms that underlie transcriptional elongation is the HIV Tat system. Briefly, in order to release the stalled state of its transcript, HIV has evolved the viral Tat protein, which binds 7SK and displaces HEXIM to hijack pTEFb. On the other hand, some cellular factors, like BRD4, achieve the same outcome without displacing HEXIM. This proposal aims to gain a mechanistic understanding of the structural state presented to all transcriptional regulators encountering an HEXIM-driven inhibitory 7SK snRNP complex, and how capture of pTEFb is achieved by the specialized HIV Tat transcriptional factor. The aims will be: (#1) to understand if the basic mechanisms are maintained in HEXIM1 and 2 and if diverse positive transcriptional regulators capitalize on the mechanism, (#2) to determine the structures of the individual RNA domains present in 7SK- snRNA and (#3) to solve the structures of both HEXIM-bound and Tat-bound complexes.