Barettino D, Vivanco Ruiz M M, Stunnenberg H G
Gene Expression Programme, EMBL, Heidelberg, Germany.
EMBO J. 1994 Jul 1;13(13):3039-49. doi: 10.1002/j.1460-2075.1994.tb06603.x.
Transcriptional activation by nuclear receptors is achieved through autonomous activation functions (AFs), a constitutive N-terminal AF-1 and a C-terminal, ligand-dependent AF-2 that comprises a motif conserved between nuclear receptors. We have performed an extensive mutational analysis of the putative AF-2 domain of chicken thyroid hormone receptor alpha (cT3R alpha). We show that the AF-2 region mediates transactivation as well as transcriptional interference (squelching), not only between the thyroid hormone and vitamin (type II) receptors, but also between type II and steroid hormone (type I) receptors. Transcriptional activation and interference require equivalent doses of the cognate ligand, and mutations in the conserved motif that reduce ligand-induced transactivation also impair transcriptional interference. When fused to the Gal4 DNA binding domain, a 35 amino acid long fragment containing the conserved motif is able to transactivate and squelch, albeit in a ligand-independent manner. Our results define the AF-2 of cT3R alpha as an autonomous transactivation domain that, in its natural context, is governed by ligand. We propose that AF-2 is probably part of a surface for interaction with either a general transcription factor or a putative bridging factor, that might be utilized by type I and II receptors.
核受体的转录激活是通过自主激活功能（AFs）实现的，即一个组成型的N端AF-1和一个C端的、依赖配体的AF-2，后者包含一个在核受体之间保守的基序。我们对鸡甲状腺激素受体α（cT3Rα）的假定AF-2结构域进行了广泛的突变分析。我们发现，AF-2区域不仅介导甲状腺激素受体和维生素（II型）受体之间的反式激活以及转录干扰（压制），还介导II型和类固醇激素（I型）受体之间的反式激活以及转录干扰。转录激活和干扰需要等量的同源配体，并且保守基序中的突变若降低配体诱导的反式激活，也会损害转录干扰。当与Gal4 DNA结合结构域融合时，一个包含保守基序的35个氨基酸长的片段能够进行反式激活和压制，尽管是以不依赖配体的方式。我们的结果将cT3Rα的AF-2定义为一个自主反式激活结构域，在其自然环境中受配体调控。我们提出，AF-2可能是与一个通用转录因子或一个假定的桥接因子相互作用表面的一部分，I型和II型受体可能会利用这一表面。
