CHROMATIN STRUCTURE AND TRANSCRIPTIONAL CONTROL ELEMENTS OF THE ERYTHROID KRUPPEL-LIKE FACTOR (EKLF) GENE

Erythroid Kruppel-like factor (EKLF) is a red cell-specific transcript ion factor whose activity is critical for the switch in expression fro m fetal to adult beta-globin during erythroid ontogeny, We have examin ed its own regulation using a number of approaches. First, the EKLF tr anscription unit is in an open chromatin configuration in erythroid ce lls. Second, in vivo transfection assays demonstrate that the more dis tal of the two erythroid-specific DNase-hypersensitive sites behaves a s an enhancer. Although this conserved element imparts high level tran scription to a heterologous promoter in all lines examined, erythroid specificity is retained only when it is fused to the proximal EKLF pro moter, which contains an important GATA site. Third, extensive mutagen esis of this enhancer element has delimited its in vivo activity to a core region of 49 base pairs. Finally, in vitro footprint and gel shif t assays demonstrate that three distinct DNA binding activities in ery throid cell extracts individually interact with three short sequences within this core enhancer element. These analyses reveal that high lev el erythroid expression of EKLF relies on the interplay between conser ved proximal and distal promoter elements that alter chromatin structu re and likely provide a target for genetic control via extracellular i nduction pathways.