TRANSCRIPTIONAL ACTIVATION BY HYPERSENSITIVE SITE 3 OF THE HUMAN BETA-GLOBIN LOCUS-CONTROL REGION IN MURINE ERYTHROLEUKEMIA-CELLS

In this paper we describe a complete deletional analysis of hypersensi tive site three (HS3) of the human beta-globin Locus Control Region (L CR). The previously defined core fragment consists of 6 footprinted re gions, with multiple binding sites for the erythroid-specific factor G ATA-1 and G-rich motifs that can interact with ubiquitous factors such as Spl and TEF-2. We show in this paper that the 5' half of this frag ment is the most important for activity in murine erythroleukemia (MEL ) cells. A fragment containing footprints 1-4 can stimulate transcript ion of a linked human beta-globin gene to levels of about 40% of that obtained with footprints 1-6. Constructs containing either footprints 1-3 or 3-6 cannot be distinguished from the beta-globin gene alone. We further show that binding sites for the erythroid-specific factor NF- E2 can co-operatively interact with parts of the HS3 core fragment, an d that HS3 requires elements upstream from -103 in the human beta-glob in promoter for full activity. The importance of these results is disc ussed in the context of the regulation of the genes in the human beta- globin cluster.