Wu J, Grindlay G J, Bushel P, Mendelsohn L, Allan M
Department of Genetics, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
Mol Cell Biol. 1990 Mar;10(3):1209-16. doi: 10.1128/mcb.10.3.1209-1216.1990.
The human epsilon-globin gene has a number of alternative transcription initiation sites which correspond with regions of DNase I hypersensitivity upstream of the canonical cap site. Transcripts originating from the promoters located -4.3/-4.5 and -1.48 kilobase pairs (kbp) and -900 and -200 base pairs (bp) upstream of the major epsilon-globin cap site can, at certain stages of erythroid differentiation, extend through the gene and are polyadenylated. The 350-bp PolIII transcripts, originating within the Alu repetitive element -2.2 kbp upstream of the cap site, extend in the opposite direction from the gene, are nonpolyadenylated, nucleus confined, and are detectable only in mature K562 cells or mature embryonic red blood cells where the epsilon-globin major cap site is maximally transcribed. Fragments containing the promoters located between -4.5 and -4.3 kbp upstream of the gene down regulate transcription from the epsilon-globin gene 20- to 30-fold in a transient expression assay in which both erythroid and nonerythroid cell lines were used. This occurs only when the direction of transcription from the -4.3/-4.5-kbp promoters is towards the gene, and we hypothesize that down regulation is caused by transcriptional interference. Fragments containing the Alu repetitive element -2.2 kbp upstream of the gene can overcome down regulation of the epsilon-globin gene by the -4.5-kbp element when interposed in the direct orientation between this element and the epsilon-globin gene.
人类ε-珠蛋白基因有多个可变转录起始位点，这些位点与经典帽位点上游的DNase I超敏区域相对应。源自位于主要ε-珠蛋白帽位点上游-4.3 / -4.5和-1.48千碱基对（kbp）以及-900和-200碱基对（bp）处启动子的转录本，在红细胞分化的某些阶段可以延伸穿过该基因并进行多聚腺苷酸化。350 bp的PolIII转录本起源于帽位点上游-2.2 kbp的Alu重复元件内，从基因向相反方向延伸，是非多聚腺苷酸化的，局限于细胞核内，并且仅在ε-珠蛋白主要帽位点转录最大化的成熟K562细胞或成熟胚胎红细胞中可检测到。在使用红细胞系和非红细胞系的瞬时表达试验中，包含位于基因上游-4.5至-4.3 kbp之间启动子的片段可将ε-珠蛋白基因的转录下调20至30倍。仅当从-4.3 / -4.5-kbp启动子的转录方向朝向该基因时才会发生这种情况，我们推测下调是由转录干扰引起的。当以直接方向插入该元件和ε-珠蛋白基因之间时，包含基因上游-2.2 kbp的Alu重复元件的片段可以克服-4.5-kbp元件对ε-珠蛋白基因的下调作用。
