Truss M, Bartsch J, Hache R S, Beato M
Institute für Molekularbiologie und Tumorforschung (IMT), Marburg, Germany.
J Steroid Biochem Mol Biol. 1993 Dec;47(1-6):1-10. doi: 10.1016/0960-0760(93)90051-w.
The MMTV promoter contains a complex hormone responsive region (HRR) upstream of a binding site for the transcription factor nuclear factor I (NFI). Hormonal induction of MMTV expression requires the integrity of both the HRR and the NFI binding site. However, in vitro NFI acts as a basal transcription factor on the MMTV promoter that does not cooperate but rather competes with the hormone receptors in terms of binding to MMTV-DNA. Fragments that contain the HRR and the NFI binding site have been reconstituted into mononucleosomes. Steroid hormone receptors bind efficiently to these nucleosomes, NFI does not. Therefore it has been postulated that the chromatin structure may be responsible for the inability of NFI to bind to the chromosomally organized inactive MMTV promoter. In vivo DNaseI and methidium-propyl-EDTA-Fe(II) (MPE) digestion pattern indicate the presence of a nucleosome covering the HRR and the NFI binding site. Genomic footprinting shows that in vivo the rotational setting of the MMTV promoter DNA in this nucleosome is identical to that previously reported for reconstituted nucleosomes in which the major grooves of the NFI half palindromes are facing towards the histone octamer and appear not to be accessible to NFI. These results indicate that MMTV promoter sequences are determining nucleosome positioning in vivo and supports the concept that rotational positioning of DNA in this nucleosome constitutively represses the MMTV promoter.
小鼠乳腺肿瘤病毒（MMTV）启动子在转录因子核因子I（NFI）的结合位点上游包含一个复杂的激素反应区域（HRR）。MMTV表达的激素诱导需要HRR和NFI结合位点两者的完整性。然而，在体外，NFI作为MMTV启动子上的基础转录因子，在与MMTV-DNA结合方面，它不与激素受体协同，而是与之竞争。包含HRR和NFI结合位点的片段已被重构成单核小体。类固醇激素受体能有效地结合这些核小体，而NFI不能。因此，有人推测染色质结构可能是NFI无法结合到染色体组织化的无活性MMTV启动子上的原因。体内脱氧核糖核酸酶I（DNaseI）和甲基丙基乙二胺铁（II）（MPE）消化模式表明存在一个覆盖HRR和NFI结合位点的核小体。基因组足迹分析表明，在体内，该核小体中MMTV启动子DNA的旋转设置与先前报道的重构成的核小体相同，其中NFI半回文序列的大沟面向组蛋白八聚体，似乎NFI无法接近。这些结果表明，MMTV启动子序列在体内决定核小体定位，并支持这样的概念，即该核小体中DNA的旋转定位持续抑制MMTV启动子。
