Human mediator enhances basal transcription by facilitating recruitment of transcription factor IIB during preinitiation complex assembly
Human mediator enhances basal transcription by facilitating recruitment of transcription factor IIB during preinitiation complex assembly
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DOI：
10.1074/jbc.m601983200
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发表时间：
2006-06-02
影响因子：
4.8
通讯作者：
Roeder, Robert G.
中科院分区：
文献类型：
--
作者：
Baek, Hwa Jin;Kang, Yun Kyoung;Roeder, Robert G.
多亚基介体是基因特异性激活剂的公认转录共激活剂。然而，最近的研究已经表明，虽然对于通过纯化的RNA聚合酶II（pol II）和一般起始因子的基础转录不是必需的，但介体对于含有更多生理互补因子的核提取物中的基础转录是必需的（Mittler，G.，Kremmer，E.，Timmers，H. T.，和Meisterernst，M.（2001）EMBO Rep.2，808 - 813; Baek，H. J.，马利克，S.，秦杰，和Roeder，R. G.等人（2002）Mol. Cell. 22，2842 - 2852）。在此，用固定的DNA模板、纯化的因子和因子耗尽的HeLa提取物进行的机制研究已经显示（i）介体增强基础转录与介体依赖性pol II和一般起始因子的募集相关（转录因子（TF）IIB和TFIIE）至启动子;（ii）都与pol II相互作用的介体和TFIIB是pol II募集到启动子所共同需要的，并且TFIIB募集是介体依赖性的，而介体募集是TFIIB非依赖性的;（iii）高水平的TFIIB可以绕过对核提取物中基础转录和pol II募集的介体要求，从而表明TFIIB功能的条件性限制和介体在克服该限制中的关键作用;和（iv）较早的限速步骤涉及TFIID-介体-启动子复合物的形成。这些结果支持一个逐步组装模型，而不是一个预先形成的全酶模型，介体依赖性组装的基础preinitiation复合物，更重要的是，确定一个步骤，涉及TFIIB作为一个关键网站的调解行动。
The multisubunit Mediator is a well established transcription coactivator for gene-specific activators. However, recent studies have shown that, although not essential for basal transcription by purified RNA polymerase II (pol II) and general initiation factors, Mediator is essential for basal transcription in nuclear extracts that contain a more physiological complement of factors (Mittler, G., Kremmer, E., Timmers, H. T., and Meisterernst, M. ( 2001) EMBO Rep. 2, 808 - 813; Baek, H. J., Malik, S., Qin, J., and Roeder, R. G. ( 2002) Mol. Cell. Biol. 22, 2842 - 2852). Here, mechanistic studies with immobilized DNA templates, purified factors, and factor-depleted HeLa extracts have shown (i) that Mediator enhancement of basal transcription correlates with Mediator- dependent recruitment of pol II and general initiation factors (transcription factor (TF) IIB and TFIIE) to the promoter; (ii) that Mediator and TFIIB, which both interact with pol II, are jointly required for pol II recruitment to the promoter and that TFIIB recruitment is Mediator- dependent, whereas Mediator recruitment is TFIIB-independent; (iii) that a high level of TFIIB can bypass the Mediator requirement for basal transcription and pol II recruitment in nuclear extract, thus indicating a conditional restriction of TFIIB function and a key role of Mediator in overcoming this restriction; and (iv) that an earlier rate-limiting step involves formation of a TFIID-Mediator-promoter complex. These results support a stepwise assembly model, rather than a preformed holoenzyme model, for Mediator-dependent assembly of a basal preinitiation complex and, more important, identify a step involving TFIIB as a key site of action of Mediator.