Fan Xiaochun, Chou Danny M, Struhl Kevin
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Nat Struct Mol Biol. 2006 Feb;13(2):117-20. doi: 10.1038/nsmb1049. Epub 2006 Jan 22.
The Mediator complex associates with eukaryotic RNA polymerase (Pol) II and is recruited to transcriptional enhancers by activator proteins. It is believed that Mediator is a general component of the Pol II machinery that is crucial to connect enhancer-bound activators to basic transcription factors. However, we show that Mediator does not detectably associate with many highly active Pol II promoters in yeast cells. Furthermore, in response to stress conditions, Mediator association is not directly related to Pol II association and in some cases is not detectable at highly activated promoters. Thus, Mediator is recruited to enhancers in an activator-specific manner, and it does not seem to be a stoichiometric component of the basic Pol II machinery in vivo. Mediator is recruited by many activators involved in stress responses, but not by the major activators that function under optimal conditions.
中介体复合物与真核生物RNA聚合酶（Pol）II结合，并通过激活蛋白被招募到转录增强子上。人们认为中介体是Pol II机制的一个普遍组成部分，对于将与增强子结合的激活蛋白与基本转录因子连接起来至关重要。然而，我们发现中介体在酵母细胞中与许多高活性的Pol II启动子没有可检测到的结合。此外，在应激条件下，中介体的结合与Pol II的结合没有直接关系，在某些情况下，在高度激活的启动子上无法检测到中介体。因此，中介体以激活蛋白特异性的方式被招募到增强子上，而且它似乎不是体内基本Pol II机制的化学计量组成部分。许多参与应激反应的激活蛋白会招募中介体，但在最佳条件下起作用的主要激活蛋白不会。
