DNasel hypersensitive sites 1, 2 and 3 of the human β-globin dominant control region direct position-independent expression

The human beta-globin dominant control region (DCR) which flanks the multigene beta-globin locus directs high level, site of integration independent, copy number dependent expression on a linked human beta-globin gene in transgenic mice and stably transfected mouse erythroleukemia (MEL) cells. We have assayed each of the individual DNaseI hypersensitive regions present in the full 15kb DCR for position independence and copy number dependence of a linked beta-globin gene in transgenic mice. The results show that at least three of the individual DNaseI hypersensitive site regions (sites 1, 2 and 3), though expressing at lower levels than the full DCR, are capable of position independent, copy number dependent expression. Site 2 alone directs the highest level of expression of the single site constructs, producing nearly 70% of the level of the full DCR. Sites 1 and 3 each provide 30% of the full activity. Deletion of either site 2 or 3 from the complete set significantly reduces the level of expression, but does not effect position independence or copy number dependence. This demonstrates that sites 2 and 3 are required for full expression and suggests that all the sites are required for the full expression of even a single gene from this multigene locus.