Globin genes exhibit tissue, developmental and maturational specificity. It is our purpose to understand the molecular basis of globin gene regulation. Our efforts have focused on the beta-globin gene cluster that contains the epsilon, gamma and beta genes expressed during the embryonic, fetal and adult developmental periods, respectively. These genes are encompassed within a 60 kb segment of DNA on human chromosome 11. Within this cluster are several cis-acting regulatory elements that interact with trans-acting factors (proteins) to modulate globin gene expression. The locus control region (LCR) located upstream from the cluster contains four regulatory elements (5'HS1-4). Other regulatory elements are contained within the individual gene promoters and enhancers are located downstream from the gamma and beta globin genes. An enhancer within 5'HS-2 interacts with an erythroid specific nuclear protein, NF-E2, to maximize hemoglobin synthesis during erythroid maturation. We have purified one component of NF-E2 from human erythroleukemia cells; this 45Kd peptide co-purifies with the enhancer binding activity but in pure form does not bind to the HS-2 enhancer suggesting the existence of a second subunit. Interaction of the HS-2 enhancer with the gamma promoter when in competition with the beta promoter appears to involve a protein that binds to the sequences between - 35 and -53 upstream from the transcriptional start site. This part of the gamma promoter appears to function as a stage selector element and the protein with which it interacts may have a critical role in developmental switching. A mutation at -202 associated with an increase in HbF in adult life creates a binding site for this protein. Butyrates induces fetal hemoglobin synthesis in adult erythroid cells. We have localized the promoter sequences required for butyrate inducibility to the to -70 to -120 segment; these sequences bind CDP-1, a potential repressor that disappears with butyrate induction.
