Urnov F D, Wolffe A P
Sangamo Biosciences, Point Richmond Tech Center, Richmond, California 94804, USA.
J Biol Chem. 2001 Jun 8;276(23):19753-61. doi: 10.1074/jbc.M100924200. Epub 2001 Mar 23.
The assembly of the genome into chromatin imposes a poorly understood set of rules and constraints on action by regulatory factors. We investigated the role played by chromatin infrastructure in enabling an acute response of the Xenopus TRbetaA gene to thyroid hormone receptor (TR), an extensively studied member of the nuclear hormone receptor superfamily. We found that in addition to the known TR response element (TRE) in the promoter, full range regulation required an upstream enhancer that contained multiple nonconsensus TREs and augmented ligand action at high receptor levels. An array of translationally positioned nucleosomes formed over the TRbetaA locus in vivo; unliganded TR engaged this array in linker DNA between two nucleosomes and via TREs on the surface of histone octamers. Remarkably, assembly of enhancer DNA into mature chromatin potentiated binding by TR to its target response elements and enabled a greater range of regulation by TR than was observed on immature chromatin templates. Because assembly of enhancer DNA into chromatin increased TR binding to the nonconsensus TREs, we hypothesize that chromatin disruption targeted by liganded TR to the enhancer may lead to receptor release from the template and to an attenuation of response to hormone.
基因组组装成染色质对调节因子的作用施加了一套理解尚不充分的规则和限制。我们研究了染色质基础结构在使非洲爪蟾TRbetaA基因对甲状腺激素受体（TR）产生急性反应中所起的作用，TR是核激素受体超家族中一个被广泛研究的成员。我们发现，除了启动子中已知的TR反应元件（TRE）外，全面的调控还需要一个上游增强子，该增强子包含多个非共识TRE，并在高受体水平增强配体作用。在体内，TRbetaA基因座上形成了一系列处于翻译定位的核小体；未结合配体的TR通过两个核小体之间的连接DNA并经由组蛋白八聚体表面的TRE与该阵列结合。值得注意的是，增强子DNA组装成成熟染色质增强了TR与其靶反应元件的结合，并使TR的调控范围比在未成熟染色质模板上观察到的更大。由于增强子DNA组装成染色质增加了TR与非共识TRE的结合，我们推测，结合配体的TR靶向增强子的染色质破坏可能导致受体从模板上释放，并导致对激素反应的减弱。
