CHROMATIN STRUCTURE IN REGULATION OF MAMMALIAN GENE EXPRESSION

胚胎ε珠蛋白基因是β珠蛋白的第一个成员 在发育过程中表达的基因家族。 表达 β-类珠蛋白基因受β-珠蛋白基因座控制 控制区（LCR），包括红细胞特异性DNA酶I 超敏位点（HS）ε-珠蛋白上游的5-18个酶 基因 LCR对细胞的染色质结构有长距离的影响。 β-珠蛋白基因座，它激活不同珠蛋白的转录 基因启动子，因为基因在 发展 我们目前对基因过程的大部分了解 已经从体外研究中获得了激活，其中DNA不 与组蛋白和其他染色体蛋白组装在一起， 原子核 为了研究基因在自然环境中的激活， 我们已经使用了含有人类染色体的微型染色体， ε-珠蛋白基因和β珠蛋白LCR增强子的部分。 色相微小染色体ε-珠蛋白基因在K562细胞中的表达 红系细胞完全依赖于存在，如果β- 顺式珠蛋白LCR。 使用限制性内切酶进入， 通过末端标记实验，我们观察到启动子和5'端 小染色体ε-珠蛋白基因近端结构区 被一系列定位的核小体覆盖。 两类研究 表明单个启动子近端核小体改变或丢失， 激活基因进行转录。 调节表达的 在微型染色体上的ε-珠蛋白基因提供了一种研究手段， 高分辨率，激活基因的启动子-增强子相互作用 在体内组装成染色质

The embryonic epsilon-globin gene is the first member of the beta-globin family of genes to be expressed during development. Expression of the beta-like-globin genes is under the control of the beta-globin locus control region (LCR), encompassing erythroid specific DNase I hypersensitive sites (HS) 5-18 kilobases upstream of the epsilon-globin gene. The LCR has long range effects on the chromatin structure of the beta-globin locus, and it activates transcription of the different globin gene promoters as the genes are expressed sequentially during development. Much of our current understanding of the process of gene activation has been gained from in vitro studies where DNA is not assembled with histones and other chromosomal proteins as it is in the nucleus. To study the activation of a gene in its natural context of chromatin in vivo we have used minichromosomes containing the human epsilon-globin gene and portions of the beta globin LCR enhancer. Expression of hue minichromosomal epsilon-globin gene in K562 human erythroid cells is completely dependent on the presense if the beta- globin LCR in cis. Using restriction endonuclease access, and indirect end labelling experiments, we have observed that the promoter and 5' proximal structural regions of the minichromosomal epsilon-globin gene are covered by an array of positioned nucleosomes. Both types of studies suggest alteration or loss of a single promoter-proximal nucleosome upon activation of the gene for transcription. Regulated expression of the epsilon-globin gene on the minichromsomes offers a means too study at high resolution, the promoter-enhancer interaction of an activated gene assembled in vivo into chromatin.