Chromatin structure and transcriptional control elements of the erythroid Kruppel-like factor (EKLF) gene

Erythroid Kruppel-like factor (EKLF) is a red cell-specific transcription factor whose activity is critical for the switch in expression from fetal to adult β-globin during erythroid ontogeny. We have examined its own regulation using a number of approaches. First, the EKLF transcription unit is in an open chromatin configuration in erythroid cells. Second, in vivo transfection assays demonstrate that the more distal of the two erythroid-specific DNase-hypersensitive sites behaves as an enhancer. Although this conserved element imparts high level transcription to a heterologous promoter in all lines examined, erythroid specificity is retained only when it is fused to the proximal EKLF promoter, which contains an important GATA site. Third, extensive mutagenesis of this enhancer element has delimited its in vivo activity to a core region of 49 base pairs. Finally, in vitro footprint and gel shift assays demonstrate that three distinct DNA binding activities in erythroid cell extracts individually interact with three short sequences within this core enhancer element. These analyses reveal that high level erythroid expression of EKLF relies on the interplay between conserved proximal and distal promoter elements that alter chromatin structure and likely provide a target for genetic control via extracellular induction pathways.