在Yunnanese（Aγδβ）^0—地贫3′缺失端点下游鉴别到两个增强子样顺序

Two Enhancer-Like Sequences Were Identified from Downstream of The 3′ Breakpoint of The Yunnanese (Aγδβ)0-thalassemia Deletion

利用荧光酶报告基因系统搜索了Yunnanese (Aγδβ) 0 地中海贫血缺失 3′端点下游 11 5kb区域内的调控顺序 .确定缺失 3′端点立即下游区 1 7kb片段 ,在人红白血病细胞K5 6 2及鼠红白血病细胞MELGM979中 ,可使γ 珠蛋白基因启动子驱动的荧光酶基因表达增加 3 8～ 4 0倍 ,而在HeLa细胞中仅增加 1 5倍 .位于缺失 3′端点约 10kb的一个长 1 4kb片段在K5 6 2和MELGM979中 ,可使γ 基因启动子驱动的荧光酶基因表达增加 2 4～2 9倍 ,而在HeLa细胞中无增加 .结果说明这两段顺序均有增强子活性 ,并且这种活性具有一定的红细胞特异性 .进一步证明 1 7kb片段内包含多个转录调节蛋白结合模体的 430bp片段包含了 1 7kb片段的大部分增强子活性 .这些结果为缺失导致增强子样顺序并入到接近Gγ 基因 ,是Yunnanese (Aγδβ) 0 地贫缺失突变体中胎儿Gγ 珠蛋白基因 ,在成人期持续活跃表达原因的假设提供了实验证据 .

The cis-acting elements were scanned within 11.5 kb of the 3′juxtaposed region of the Yunnanese (Aγδβ) 0-thalassemia deletion using the luciferase report gene system. A 1.7 kb fragment immediately downstream of the 3′ breakpoint of the deletion was found to increase expression of the luciferase gene driven by Gγ-globin gene promoter by 3.8 to 4.0 fold in K562 cells and MELGM979 cells and 1.5 fold in HeLa cells. A 1.4 kb fragment that is located 10 kb downstream of the 3′ breakpoint was found to increase the luciferase expression by 2.4 to 2.9 fold in K562 cells and MELGM979 cells but no enhancement in HeLa cells. The results suggested that the two fragments contain enhancer-like elements and they function in a certain erythroid-specific manner. Furthermore, a 430 bp region that contains several putative motifs for known transacting factors binding within the 1.7 kb fragment was showed to include the most of the enhancer activity of the fragment. These results provided experimental proof for the hypothesis that the importation of enhancer-like sequences into the vicinity of Gγ globin gene may be responsible for the reactivation of the Gγ-globin gene in the Yunnanese (Aγδβ) 0-thalassemia mutant.