Guermah M, Tao Y, Roeder R G
Laboratory of Biochemistry and Molecular Biology, The Rockefeller University, New York, New York 10021, USA.
Mol Cell Biol. 2001 Oct;21(20):6882-94. doi: 10.1128/MCB.21.20.6882-6894.2001.
Human transcription factor TFIID contains the TATA-binding protein (TBP) and several TBP-associated factors (TAF(II)s). To elucidate the structural organization and function of TFIID, we expressed and characterized the product of a cloned cDNA encoding human TAF(II)135 (hTAF(II)135). Comparative far Western blots have shown that hTAF(II)135 interacts strongly with hTAF(II)20, moderately with hTAF(II)150, and weakly with hTAF(II)43 and hTAF(II)250. Consistent with these observations and with sequence relationships of hTAF(II)20 and hTAF(II)135 to histones H2B and H2A, respectively, TFIID preparations that contain higher levels of hTAF(II)135 also contain higher levels of hTAF(II)20, and the interaction between hTAF(II)20 and hTAF(II)135 is critical for human TFIID assembly in vitro. From a functional standpoint, hTAF(II)135 has been found to interact strongly and directly with hTFIIA and (within a complex that also contains hTBP and hTAF(II)250) to specifically cooperate with TFIIA to relieve TAF(II)250-mediated repression of TBP binding and function on core promoters. Finally, we report a functional synergism between TAF(II)s and the TRAP/Mediator complex in activated transcription, manifested as hTAF(II)-mediated inhibition of basal transcription and a consequent TRAP requirement for both a high absolute level of activated transcription and a high and more physiological activated/basal transcription ratio. These results suggest a dynamic TFIID structure in which the switch from a basal hTAF(II)-enhanced repression state to an activator-mediated activated state on a promoter may be mediated in part through activator or coactivator interactions with hTAF(II)135.
人类转录因子TFIID包含TATA结合蛋白（TBP）和几种TBP相关因子（TAF（II）s）。为了阐明TFIID的结构组织和功能，我们表达并鉴定了编码人类TAF（II）135（hTAF（II）135）的克隆cDNA的产物。比较远缘蛋白质免疫印迹表明，hTAF（II）135与hTAF（II）20强烈相互作用，与hTAF（II）150中度相互作用，与hTAF（II）43和hTAF（II）250弱相互作用。与这些观察结果以及hTAF（II）20和hTAF（II）135分别与组蛋白H2B和H2A的序列关系一致，含有较高水平hTAF（II）135的TFIID制剂也含有较高水平的hTAF（II）20，并且hTAF（II）20和hTAF（II）135之间的相互作用对于体外人类TFIID组装至关重要。从功能角度来看，已发现hTAF（II）135与hTFIIA强烈且直接相互作用，并且（在还包含hTBP和hTAF（II）250的复合物中）与TFIIA特异性协同作用，以减轻TAF（II）250介导的对TBP结合和在核心启动子上功能的抑制。最后，我们报道了TAF（II）s与TRAP/中介体复合物在激活转录中的功能协同作用，表现为hTAF（II）介导的基础转录抑制以及因此TRAP对于高绝对水平的激活转录和高且更接近生理水平的激活/基础转录比的需求。这些结果表明存在一种动态的TFIID结构，其中启动子上从基础hTAF（II）增强的抑制状态到激活剂介导的激活状态的转变可能部分通过激活剂或共激活剂与hTAF（II）135的相互作用来介导。
