Model for β-LCR activation during hematopoietic cell differentiation. It is proposed that, in the uncommitted cells, the locus is in a closed chromatin configuration, shown in the diagram by the dashed lines. However, constitutive transcription factors are bound to LCR sequences and certain DNaseI hypersensitive sites (shown as • in the diagram) are formed. In erythroid progenitors all the DNaseI HS sites are formed and the LCR holocomplex is generated. The locus attains an intermediate stage of DNaseI sensitivity (shown by the sparse dashed lines). The locus becomes fully active when, in the erythroblasts, the transcriptional complexes interact with the globin gene promoters and the promoter-specific DNaseI hypersensitive sites are formed.