Muscat G E, Burke L J, Downes M
University of Queensland, Centre for Molecular and Cellular Biology, Ritchie Research Laboratories, B402A, St Lucia 4072, Queensland, Australia.
Nucleic Acids Res. 1998 Jun 15;26(12):2899-907. doi: 10.1093/nar/26.12.2899.
Repression of transcription by the classical nuclear receptors (e.g. TR, RAR), the orphan nuclear receptors (e.g. Rev-erbAalpha/beta), Mxi-1 and Mad bHLH-zip proteins and the oncoproteins PLZF and LAZ3/BCL6 is mediated by the corepressors N-CoR and SMRT. The interaction of the corepressors with the components involved in chromatin remodelling, such as the recruiting proteins Sin3A/B and the histone deacteylases HDAc-1 and RPD3, has been analysed in detail. The N-CoR/Sin3/HDAc complexes have a key role in the regulation of cellular proliferation and differentiation. However, the interaction of these corepressors with the basal transcriptional machinery has remained obscure. In this study we demonstrated that the N-terminalrepression domains and the receptor interactiondomains (RID) of N-CoR and its splice variants, RIP13a and RIP13Delta1, directly interact with TAFII32 in vivo and in vitro . We show that interaction domain II within the N-CoR and RIP13a RID is required for the interaction with TAFII32. We also observed that N-CoR directly interacts with each of the basal factors, TFIIB and TAFII70, and can simultaneously interact with all three basal factors in a non-competitive manner. Furthermore, we provide evidence that suggests the RVR/Rev-erbbeta-corepressor complex also interacts with the general transcriptional machinery, and that the physicalassociation of TFIIB with N-CoR also occurs in the presence of Sin3B and HDAc-1. Interestingly, we observed that N-CoR expression ablated the functional interaction between TFIIB and TAFII32 that is critical to the initiation of transcription. In conclusion, this study demonstrates that the N-terminal repressor region and the C-terminal RIDs are part of the corepressor contact interface that mediates the interaction with the general transcription factors, and demonstrates that TAFs can also directly interact with corepressors to mediate signals from repressors to the basal machinery. We also suggest that N-CoR interacts with the central components of the transcriptional initiation process (TFIIB, TAFs) and locks them into a non-functional complex or conformation that is not conducive to transcription.
经典核受体（如甲状腺激素受体、视黄酸受体）、孤儿核受体（如Rev-erbAα/β）、Mxi-1和Mad碱性螺旋-环-螺旋拉链蛋白以及癌蛋白PLZF和LAZ3/BCL6对转录的抑制作用是由共抑制因子N-CoR和SMRT介导的。共抑制因子与参与染色质重塑的成分（如募集蛋白Sin3A/B以及组蛋白去乙酰化酶HDAc-1和RPD3）之间的相互作用已得到详细分析。N-CoR/Sin3/HDAc复合物在细胞增殖和分化的调控中起关键作用。然而，这些共抑制因子与基础转录机制之间的相互作用仍不清楚。在本研究中，我们证明了N-CoR及其剪接变体RIP13a和RIP13Delta1的N端抑制结构域和受体相互作用结构域（RID）在体内和体外均能直接与TAFII32相互作用。我们发现N-CoR和RIP13a RID内的相互作用结构域II是与TAFII32相互作用所必需的。我们还观察到N-CoR能直接与基础因子TFIIB和TAFII70中的每一个相互作用，并且能以非竞争性方式同时与所有这三个基础因子相互作用。此外，我们提供的证据表明RVR/Rev-erbβ-共抑制因子复合物也与一般转录机制相互作用，并且在有Sin3B和HDAc-1存在的情况下TFIIB与N-CoR之间也会发生物理结合。有趣的是，我们观察到N-CoR的表达消除了TFIIB与TAFII32之间对转录起始至关重要的功能性相互作用。总之，本研究表明N端抑制区域和C端RID是共抑制因子接触界面的一部分，该界面介导了与一般转录因子的相互作用，并证明TAFs也能直接与共抑制因子相互作用，以介导从抑制因子到基础机制的信号传递。我们还提出N-CoR与转录起始过程的核心成分（TFIIB、TAFs）相互作用，并将它们锁定在一个无功能的复合物或不利于转录的构象中。
