The EMBO Journal Vol.16 No.11 pp.3158–3171, 1997 Determinants of chromatin disruption and transcriptional regulation instigated by the thyroid hormone receptor: hormone-regulated chromatin disruption is not sufficient for transcriptional activation Jiemin Wong, Yun-Bo Shi and the presence of T3. The exact molecular mechanism by Alan P.Wolffe1,2 which they inhibit transcription is unknown. In addition, the TR itself makes contact with components of the basal Unit on Molecular Morphogenesis and 1Section on Molecular Biology, transcriptional machinery including TFIIB (Baniahmad Laboratory of Molecular Embryology, National Institute of Child Health and Human Development, NIH, Bldg 18T, Rm 106, Bethesda, et al., 1993; Fondell et al., 1993; Hadzic et al., 1995). MD 20892-5431, USA Several structurally independent domains of the TR are required for silencing, these include regions that do not 2Corresponding author e-mail:
[email protected] interact with TFIIB (Baniahmad et al., 1993), indicative of multiple silencing mechanisms (Baniahmad et al., 1992, Chromatin disruption and transcriptional activation 1995a; Damm and Evans, 1993; Lee and Mahdavi, 1993; are both thyroid hormone-dependent processes regu- Qi et al., 1995; Uppaluri and Towle, 1995; Wagner et al., lated by the heterodimer of thyroid hormone receptor 1995). Transcriptional activation by the TR also involves and 9-cis retinoic acid receptor (TR–RXR). In the multiple structurally independent domains. A ligand- absence of hormone, TR–RXR binds to nucleosomal dependent transactivation domain (AF2) is located at the DNA, locally disrupts histone–DNA contacts and gener- carboxy-terminus of the receptor (Zenke et al., 1990; ates a DNase I-hypersensitive site.