Widłak P, Garrard W T
Department of Experimental and Clinical Radiobiology, Institute of Oncology, Gliwice, Poland.
Acta Biochim Pol. 1998;45(1):209-19.
Packaging of DNA into chromatin adds complexity to the problem of regulation of gene expression. Nucleosomes affect the accessibility of transcription factors to occupy their binding sites in chromatin of eukaryotic cells. The disruption of nucleosome structure within the enhancer/promoter region of the integrated HIV-1 proviral genome is an instructive example of a chromatin remodeling process during transcriptional activation. To investigate the mechanism responsible for generating nuclease hypersensitive sites that exist in vivo in the promoter/enhancer region of the 5'LTR (long terminal repeat) of integrated HIV-1 we have utilized an in vitro chromatin assembly system with Xenopus oocyte extracts. Chromatin assembly in the presence of Sp1 and NFkappaB transcription factors induces DNase I hypersensitive sites on either side of their binding sites and positions the adjacent nucleosomes. This structure can also be formed in a factor-induced, ATP-dependent chromatin remodeling process and closely resembles the in vivo chromatin structure. The DNase I hypersensitive sites that form within the HIV LTR are probably histone-free and remain after removal of transcription factors.
将DNA包装成染色质增加了基因表达调控问题的复杂性。核小体影响转录因子在真核细胞染色质中占据其结合位点的可及性。整合的HIV-1前病毒基因组增强子/启动子区域内核小体结构的破坏是转录激活过程中染色质重塑过程的一个有启发性的例子。为了研究在整合的HIV-1的5'LTR（长末端重复序列）启动子/增强子区域中体内存在的核酸酶超敏位点产生的机制，我们利用了爪蟾卵母细胞提取物的体外染色质组装系统。在Sp1和NFκB转录因子存在的情况下进行染色质组装，会在它们结合位点的两侧诱导产生DNase I超敏位点，并定位相邻的核小体。这种结构也可以在因子诱导的、ATP依赖的染色质重塑过程中形成，并且与体内染色质结构非常相似。在HIV LTR内形成的DNase I超敏位点可能不含组蛋白，并且在去除转录因子后仍然存在。
