Nucleic Acids Research
HS-40 is the major regulatory element of the human α-globin locus, located 40 kb upstream of the ζ-globin gene. To test for potential interactions between HS-40 and the β- or the γ-globin gene promoters in stable transfection assays, the HS-40 core sequence was cloned upstream of either the β promoter or the γ promoter driving the neomycin phosphotransferase gene and enhancer activity was measured using a colony assay. In K562 or in MEL cells, enhancer activity of HS-40 was higher than that of the individual core sequences of the DNase I hypersensitive sites (HS) of the β-globin locus control region (LCR), and ∼60% of the enhancer activity of a 2.5 kb μLCR, which contains the core elements of DNase I hypersensitive sites 1–4. In contrast to the synergistic interaction between the DNase I hypersensitive sites of β locus LCR, combination of HS-40 with these DNase I hypersensitive sites failed to display cooperativity in K562 cells and inhibited enhancer function in MEL cells. Inhibition of enhancer function was also observed when two copies of the HS-40 were arranged tandemly. We conclude that the core element of HS-40 (i) is a powerful enhancer of γ- and β-globin gene expression, (ii) in contrast to other classical enhancers, acts best as a single copy, (iii) does not cooperate with the regulatory elements of the β-globin locus control region.
Chen, Hsiaoli; Lowrey, Christopher H.; and Stamatoyannopoulos, George, "Analysis of Enhancer Function of the HS-40 Core Sequence of the Human Alpha-Globin Cluster" (1997). Open Dartmouth: Faculty Open Access Scholarship. 3816.