Detailed analysis of the site 3 region of the human beta-globin dominant control region.

Four DNase I hypersensitive sites characterize the human beta-globin Dominant Control Region (DCR) providing position independent, high levels of erythroid specific expression to linked homologous and heterologous genes when introduced into cultured cells or in transgenic mice. We have delineated the hypersensitive site located 10.5 kbp upstream of the epsilon-globin gene by short range DNase I sensitivity mapping to a 600 bp region. Using transgenic mice and MEL cells the functional part of this region was further mapped to a 300 bp central core, which provides position independent, high level expression. It contains a number of ubiquitous and erythroid specific protein binding sites, including the previously described factors NF-E1 (GF1) and NF-E2. The latter binds to a dimer of the consensus binding sequence for jun/fos. The presence of this sequence is required for the function of the element, but single or multimerized copies of this site failed to give position independent, high levels of expression in transgenic mice or MEL cells. We therefore conclude that a combination of factor binding sites is necessary to allow site 3 to function as a strong transcriptional activator, resulting in position independent expression of the beta-globin gene.