Antes T J, Namciu S J, Fournier R E, Levy-Wilson B
Research Institute, Palo Alto Medical Foundation, Palo Alto, California 94301, USA.
Biochemistry. 2001 Jun 12;40(23):6731-42. doi: 10.1021/bi0100743.
The 5' boundary of the chromosomal domain of the human apolipoprotein B (apoB) gene in intestinal cells has been localized and characterized. It is composed of two kinds of boundary elements; the first, functional boundary is an insulator activity exhibited by a 1.8 kb DNA fragment located between -58 and -56 kb upstream of the human apoB promoter. In this region, an enhancer-blocking activity has been mapped to a CTCF binding site that is located upstream of two apoB intestinal enhancers (IEs), the 315 IE and the 485 IE. The CTCF site represents a boundary between two types of chromatin structure: an open, DNaseI-sensitive region 3' of the CTCF site containing the intestinal regulatory elements and a closed, DNaseI-resistant region 5' of the CTCF site. The 1.8 kb fragment harboring the CTCF site also insulated mini-white transgenes against position effects in Drosophila melanogaster. The second, structural boundary is represented by a nuclear matrix attachment region (MAR), situated about 3 kb 5' of the CTCF site. This MAR may represent the 5' anchorage site for a chromosomal loop that functions to bring the intestinal regulatory elements closer to the apoB promoter.
人类载脂蛋白B（apoB）基因在肠道细胞中染色体结构域的5'边界已被定位并进行了特征描述。它由两种边界元件组成；第一种功能性边界是一种绝缘活性，由位于人类apoB启动子上游-58至-56 kb之间的一个1.8 kb DNA片段表现出来。在该区域，增强子阻断活性已被定位到一个CTCF结合位点，该位点位于两个apoB肠道增强子（IEs），即315 IE和485 IE的上游。CTCF位点代表了两种染色质结构之间的边界：CTCF位点3'端的一个开放的、对DNaseI敏感的区域，包含肠道调控元件，以及CTCF位点5'端的一个封闭的、对DNaseI有抗性的区域。含有CTCF位点的1.8 kb片段也能使微型白色转基因在黑腹果蝇中免受位置效应的影响。第二种结构边界由一个核基质附着区域（MAR）代表，位于CTCF位点5'端约3 kb处。这个MAR可能代表一个染色体环的5'锚定位点，该染色体环的作用是使肠道调控元件更靠近apoB启动子。
