A novel regulatory element of the human α-globin gene responsible for its constitutive expression

The α-globin gene is expressed at a constitutively high level upon gene transfer into both erythroid and nonerythroid cells. The β-globin gene, on the other hand, is dependent on the presence of a linked viral enhancer for its efficient expression upon transfer into heterologous cells. In this report, we describe a novel regulatory element within the structural α-globin gene which can activate its own promoter to result in a high level of expression in both erythroid and non-erythroid cells. This regulatory element does not appear to have the properties of a classical enhancer. While this element exerts a positive effect on its own promoter, we have demonstrated in a previous study that the same element exerts a negative effect on heterologous genes such as the β- and γ-globin genes. In this study, we localize this element to a 259-nucleotide fragment immediately downstream from the translation initiation codon which is partially overlapped by a DNase I hypersensitive domain only in erythroid cells. We propose that this element may activate the α-globin gene promoter in all cell types in vivo as it does in vitro. The specificity of erythroid expression of the α-globin gene in vivo is probably determined by a "permissive" chromatin configuration in erythroid cells and a "nonpermissive" configuration in non-erythroid cells.