hnRNP U Inhibits Carboxy-Terminal Domain Phosphorylation by TFIIH and Represses RNA Polymerase II Elongation
hnRNP U Inhibits Carboxy-Terminal Domain Phosphorylation by TFIIH and Represses RNA Polymerase II Elongation
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DOI：
10.1128/mcb.19.10.6833
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发表时间：
1999-10
影响因子：
5.3
通讯作者：
Myung-Kuk Kim;V. Nikodem
中科院分区：
文献类型：
--
作者：
Myung-Kuk Kim;V. Nikodem
摘要本研究描述了hnRNP U作为RNA聚合酶(POL II)延长抑制剂的潜在新功能。我们证明了人hnRNP U的一个亚组分在体内与Pol II全酶相关，并因此作为预引发复合体的一部分被招募到启动子。然而，hnRNP U似乎在转录的早期阶段从POL II复合体中解离出来，因此没有出现在延长的POL II复合体中。当在人类免疫缺陷病毒1型转录系统中测试时，hnRNP U抑制Pol II的延伸而不是启动转录。这种抑制需要Pol II的羧基末端结构域(CTD)。我们发现在一定条件下hnRNP U可以在体内结合TFIIH，并在体外抑制TFIIH介导的CTD磷酸化。我们发现hnRNP U的中间结构域足以介导它与Pol II的结合，以及它对TFIIH介导的磷酸化和Pol II延伸的抑制。HnRNP U抑制TFIIH介导的CTD磷酸化及其与Pol II结合的能力是hnRNP U介导抑制Pol II延长所必需的。基于这些观察，我们认为hnRNP U的一个亚组分作为Pol II全酶的一个组成部分，可能下调了TFIIH介导的基础转录机制中CTD的磷酸化，并抑制了Pol II的延伸。通过这些功能，hnRNP U可能提供了在POL II全酶中维持CTD处于非磷酸化状态的机制之一。
ABSTRACT This study describes a potential new function of hnRNP U as an RNA polymerase (Pol II) elongation inhibitor. We demonstrated that a subfraction of human hnRNP U is associated with the Pol II holoenzyme in vivo and as such recruited to the promoter as part of the preinitiation complex. hnRNP U, however, appears to dissociate from the Pol II complex at the early stage of transcription and is therefore absent from the elongating Pol II complex. When tested in the human immunodeficiency virus type 1 transcription system, hnRNP U inhibits elongation rather than initiation of transcription by Pol II. This inhibition requires the carboxy-terminal domain (CTD) of Pol II. We showed that hnRNP U can bind TFIIH in vivo under certain conditions and inhibit TFIIH-mediated CTD phosphorylation in vitro. We find that the middle domain of hnRNP U is sufficient to mediate its Pol II association and its inhibition of TFIIH-mediated phosphorylation and Pol II elongation. The abilities of hnRNP U to inhibit TFIIH-mediated CTD phosphorylation and its Pol II association are necessary for hnRNP U to mediate the repression of Pol II elongation. Based on these observations, we suggest that a subfraction of hnRNP U, as a component of the Pol II holoenzyme, may downregulate TFIIH-mediated CTD phosphorylation in the basal transcription machinery and repress Pol II elongation. With such functions, hnRNP U might provide one of the mechanisms by which the CTD is maintained in an unphosphorylated state in the Pol II holoenzyme.