Tat-Host Transcription Complexes

Tat是一种小的HIV调节蛋白，对病毒复制至关重要，其众所周知的功能是增强 病毒启动子的转录延伸。TAT招募宿主延伸因子P-TEFb到TAR RNA以 磷酸化RNAP II的CTD。P-TEFb的CDK9激酶活性被7SK SnRNP抑制， 我们之前发现，被抑制的复合体在转录过程中被招募到HIV启动子 当合成焦油时，它被排出，从而激活了该激酶。另一组主机因素， 超伸长复合体(SEC)，稍后运行以进一步增强TAT介导的伸长。已经有了 TAT及其络合物结构研究的最新进展，尤其是与P-TEFb结合的TAT 和证券交易委员会的组成部分。很明显，Tat是一种很大程度上无序的蛋白质，需要P-TEFb 其折叠的模板，主要通过与细胞周期蛋白T1亚基的相互作用。尽管取得了这些进展，但 转录过程相当复杂和动态，许多其他寄主因素也起到了作用。基于我们的 以前的HARC蛋白质组研究，我们最近发现了几个新的TAT辅助因子，对其 功能。一种名为PJA2的因子以非降解的方式直接泛化TAT上的赖氨酸，以刺激其 活动。另一组三个因子-ZFP91、UBE2O和NAP1L4-形成细胞质复合体(ZUN)，该复合体 通过泛素化7SK SnRNP的一个亚基HEXIM1来增强TAT活性。这种非降解性物质 由UBE2O连接酶进行的修饰有助于分解抑制的7SK复合体并释放PTEFb 从细胞质重新定位到细胞核。在这些新发现的基础上，我们将进一步 TAT和宿主络合物的结构研究：1)PJA2泛素化TAT并测定 相关络合物的结构；2)用新的7SK SnRNP络合物确定TAT的结构； 检查7SK SnRNP复合体与SEC之间的联系。PJA2和ZUN的发现 复合体说明了HIV劫持宿主泛素化机制以增强其 复制。这些新的TAT转录复合体的高级结构知识将解释它们的 作用机制不仅对病毒，而且对宿主细胞转录。

Tat is a small HIV regulatory protein essential for viral replication whose well-known function is to enhance transcription elongation from the viral promoter. Tat recruits the host elongation factor P-TEFb to TAR RNA to phosphorylate the CTD of RNAP II. The activity of the Cdk9 kinase of P-TEFb is inhibited by the 7SK snRNP, and we previously found that the inhibited complex is recruited to the HIV promoter during transcription initiation and is ejected when TAR is synthesized thereby activating the kinase. Another set of host factors, the super-elongation complex (SEC), operates later to further enhance Tat-mediated elongation. There has been substantial recent progress on structural studies of Tat and its complexes, most notably Tat bound to P-TEFb and components of the SEC. It is clear that Tat is a largely disordered protein that requires the P-TEFb template for its folding, primarily through interactions with the cyclin T1 subunit. Despite this progress, the transcription process is quite complex and dynamic and many other host factors come into play. Based on our previous HARC proteomic studies, we have recently identified several new Tat cofactors important for its function. One factor, PJA2, directly ubiqutinates lysines on Tat in a non-degradative manner to stimulate its activity. Another set of three factors – ZFP91, UBE2O, and NAP1L4 – forms a cytoplasmic complex (ZUN) that enhances Tat activity via ubiquitination of HEXIM1, a subunit of the 7SK snRNP. This non-degradative modification, carried out by the UBE2O ligase, helps disassemble the inhibitory 7SK complex and releases PTEFb to relocalize from the cytoplasm to the nucleus. Based on these novel findings, we will further our structural studies of Tat and host complexes by: 1) examining ubiquitination of Tat by PJA2 and determining structures of relevant complexes; 2) determining structures of Tat with novel 7SK snRNP complexes; and 3) examining connections between 7SK snRNP complexes and the SEC. The discovery of the PJA2 and ZUN complexes illustrates another way in which HIV has hijacked the host ubiquitination machinery to enhance its replication. Advancing structural knowledge of these new Tat transcription complexes will illuminate their mechanisms of action not only for the virus but also for host cell transcription.