James-Pederson M, Yost S, Shewchuk B, Zeigler T, Miller R, Hardison R
Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park 16802.
J Biol Chem. 1995 Feb 24;270(8):3965-73. doi: 10.1074/jbc.270.8.3965.
Despite their descent from a common ancestral gene and the requirement for coordinated, tissue-specific regulation, the alpha- and beta-globin genes in many mammals are regulated in distinctly different ways. Unlike the beta-globin gene, the rabbit alpha-globin gene is transiently expressed at a high level without an added enhancer in transfected erythroid and non-erythroid cells. By examining a series of alpha/beta fusion genes, we show that internal sequences of the rabbit alpha-globin gene (within the first two exons and introns) are required along with the 5' flank for this enhancer-independent expression. Furthermore, deletion of the introns of the alpha-globin gene, or replacement by introns of the beta-globin gene, results in severely decreased expression of the transfecting genes. Hybrid constructs between segments of the alpha-globin gene and a luciferase gene confirm that internal alpha-globin sequences are needed for high level production of RNA in transfected cells. The flanking and internal sequences implicated in regulation of the rabbit alpha-globin gene coincide with a prominent CpG-rich island and may comprise an extended promoter (including both flanking and intragenic sequences) that is active in transfected cells without an enhancer.
尽管α-和β-珠蛋白基因起源于共同的祖先基因，且需要协调的组织特异性调控，但许多哺乳动物中的α-和β-珠蛋白基因的调控方式却截然不同。与β-珠蛋白基因不同，兔α-珠蛋白基因在转染的红细胞和非红细胞中无需添加增强子即可短暂高水平表达。通过研究一系列α/β融合基因，我们发现兔α-珠蛋白基因的内部序列（在前两个外显子和内含子内）与5'侧翼序列一起对于这种不依赖增强子的表达是必需的。此外，删除α-珠蛋白基因的内含子，或用β-珠蛋白基因的内含子替代，会导致转染基因的表达严重下降。α-珠蛋白基因片段与荧光素酶基因之间的杂交构建体证实，内部α-珠蛋白序列是转染细胞中高水平RNA产生所必需的。与兔α-珠蛋白基因调控相关的侧翼和内部序列与一个显著的富含CpG的岛重合，可能构成一个在没有增强子的情况下在转染细胞中活跃的扩展启动子（包括侧翼和基因内序列）。
