Many hemoglobinopathies are associated with mutations in the human Beta-globin gene locus and are characterized by diminished expression of one or several of the Beta-like globin genes. It is estimated that 3% of the world population carry mutations in the Beta globin locus and suffer from mild or severe anemia. The human Beta-globin genes are expressed in erythroid cells and are arranged in linear order on chromosome 11. The order of the genes reflects the timing of expression of individual globin genes during erythroid development. Recent work demonstrated that the locus control region (LCR), a powerful genetic DNA regulatory element located far upstream of the globin genes, is required for high-level globin gene expression throughout erythroid development. The LCR is composed of several regulatory modules that exhibit heightened sensitivity to various endo-nucleases. These sites are called hypersensitive (HS) sites and are binding sites for erythroid specific and ubiquitously expressed proteins. Although there is considerable debate as to how the LCR activates globin gene transcription, accumulating data suggest that in the human locus the individual HS sites cooperate to generate a higher order structure, referred to as the LCR holocomplex. The LCR holocomplex is thought to be generated by massive protein-DNA and protein-protein interactions that bring together the individual HS sites. In addition, recent data suggest that one of the functions attributable to the LCR is to serve as a primary attachment site for macromolecular complexes involved in chromatin remodeling and transcription. These macromolecular complexes are used to establish accessible chromatin domains and are subsequently transferred to individual globin gene promoters in a developmental stage specific manner. This proposal is aimed at addressing specific questions arising from this model. If correct, the model would explain locus control region function and would fundamentally contribute to understanding long-range regulation of chromatin structure and gene expression. It is expected that elucidating the mechanisms of globin gene regulation will benefit therapeutic attempts to treat hemoglobinopathies by introducing expression vectors mediating high-levels of wild-type Beta-globin gene expression into patients.
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