Activation of beta-major globin gene transcription is associated with recruitment of NF-E2 to the beta-globin LCR and gene promoter

The mouse beta -globin gene locus control region (LCR), located upstream of the beta -globin gene cluster, is essential for the activated transcriptio n of genes in the cluster. The LCR contains multiple binding sites for tran sactivators, including Maf-recognition elements (MARES). However, little is known about the specific proteins that bind to these sites or the time at which they bind during erythroid differentiation. We have performed chromat in immunoprecipitation experiments to determine the recruitment of the eryt hroid-specific transactivator p45 NF-E2/MafK (p18 NF-E2) heterodimer and sm all Maf proteins to various regions in the globin gene locus before and aft er the induction of murine erythroleukemia (MEL) cell differentiation. We r eport that, before induction, the LCR is occupied by small Maf proteins, an d, on erythroid maturation, the NF-E2 complex is recruited to the LCR and t he active globin promoters, even though the promoters do not contain MARES. This differentiation-coupled recruitment of NF-E2 complex correlates with a greater than 100-fold increase in beta -major globin transcription, but i s not associated with a significant change in locus-wide histone H3 acetyla tion. These findings suggest that the beta -globin gene locus exists in a c onstitutively open chromatin conformation before terminal differentiation, and we speculate that recruitment of NF-E2 complex to the LCR and active pr omoters may be a rate-limiting step in the activation of beta globin gene e xpression.