Identification and characterization of a beta-globin promoter-binding factor from murine erythroleukemia cells

We have identified a DNA-binding activity with specificity for the beta DRE, an evolutionarily conserved transcriptional regulatory element in mammalian adult beta-globin promoters. This binding activity, which we term beta DRf, for beta-globin direct repeat factor, was detected in fractionated nuclear extracts from the murine erythroleukemia cell line and has been partially purified from undifferentiated cells. beta DRf makes symmetric contacts on the two copies of its recognition sequence on both strands and introduces a bend into the DNA helix upon binding. While the factor displays a low binding affinity for the beta DRE in isolation, it binds to the intact beta-globin promoter and DNA fragments containing multiple beta DRE-binding sites with high affinity. A correlation between beta DRf binding affinity and transcriptional activity of beta DRE mutant promoters suggests that this factor stimulates transcription of the beta-globin promoter in vivo.