Globin genes are expressed quantitatively at a high level in a regulated manner, both with respect to transcription of individual members of the alpha- and beta-like families and to their expression only within the erythroid lineage of hematopoietic cells. Although the structures of the globin genes are fully defined and much is known about mutations that interfere with globin synthesis in the thalassemia syndromes, the mechanism responsible for regulation of globin genes during development or quantitatively thereafter are poorly understood. The proposed studies are aimed at (1) characterizing, purifying, and cloning cDNA for an apparently erythroid-specific DNA-binding factor that interacts with sequences upstream of the human gamma (fetal)- globin genes; (2) determining the role of this factor in the normal regulation of gamma-globin expression and in overexpression seen in hereditary persistence of fetal hemoglobin (HPFH) syndromes; (3) identifying further genes that are targets for regulation by this factor during coordinated expression characteristic of developing cells; and (4) exploring the nature of a DNA enhancer element found upstream of the embryonic (epsilon) globin gen, characterizing interacts with the gamma-globin promoter in the -170 to -195 region and encompasses the conserved octamer-motif (-175 to -182) while not interacting appreciably with the octanucleotide per se. Instead, the factor (designated GF-1) interacts strongly with nucleotides on either side of the octamer, particularly those to the 5' direction. Study of transient expression of in vitro mutagenized promoters suggest that GF-1 mediates the increased promoter strength manifest by the -175 T-C substitution naturally observed in the HPFH syndrome. Although it is apparent that many cis- and trans-acting elements and factors, coupled with organization of chromosomal domains, ultimately contribute to the complex, highly regulated pattern of globin expression in erythroid cells, our hypothesis is that detailed analysis of specific components, as proposed in application, will provide new insights and avenues to pursue in the understanding of the human globin gene system in both normal and pathologic states.
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