Wong J, Li Q, Levi B Z, Shi Y B, Wolffe A P
Laboratory of Molecular Embryology, National Institute of Child Health and Human Development, NIH, Building 18T, Room 106, Bethesda, MD 20892-5431, USA.
EMBO J. 1997 Dec 1;16(23):7130-45. doi: 10.1093/emboj/16.23.7130.
The Xenopus thyroid hormone receptor betaA (TRbetaA) gene contains an important thyroid hormone response element (TRE) that is assembled into a positioned nucleosome. We determine the translational position of the nucleosome containing the TRE and the rotational positioning of the double helix with respect to the histone surface. Histone H1 is incorporated into the nucleosome leading to an asymmetric protection to micrococcal nuclease cleavage of linker DNA relative to the nucleosome core. Histone H1 association is without significant consequence for the binding of the heterodimer of thyroid hormone receptor and 9-cis retinoic acid receptor (TR/RXR) to nucleosomal DNA in vitro, or for the regulation of TRbetaA gene transcription following microinjection into the oocyte nucleus. Small alterations of 3 and 6 bp in the translational positioning of the TRE in chromatin are also without effect on the transcriptional activity of the TRbetaA gene, whereas a small change in the rotational position of the TRE (3 bp) relative to the histone surface significantly reduces the binding of TR/RXR to the nucleosome and decreases transcriptional activation directed by TR/RXR. Our results indicate that the specific architecture of the nucleosome containing the TRE may have regulatory significance for expression of the TRbetaA gene.
非洲爪蟾甲状腺激素受体βA（TRbetaA）基因包含一个重要的甲状腺激素反应元件（TRE），该元件组装成一个定位核小体。我们确定了包含TRE的核小体的平移位置以及双螺旋相对于组蛋白表面的旋转定位。组蛋白H1被整合到核小体中，导致相对于核小体核心，连接DNA对微球菌核酸酶切割的不对称保护。组蛋白H1的结合对甲状腺激素受体和9-顺式视黄酸受体（TR/RXR）异二聚体在体外与核小体DNA的结合，或对微注射到卵母细胞核后TRbetaA基因转录的调控没有显著影响。染色质中TRE平移位置上3个和6个碱基对的微小改变对TRbetaA基因的转录活性也没有影响，而TRE相对于组蛋白表面的旋转位置有一个小的变化（3个碱基对）会显著降低TR/RXR与核小体的结合，并降低TR/RXR介导的转录激活。我们的结果表明，包含TRE的核小体的特定结构可能对TRbetaA基因的表达具有调控意义。
