FIGURE 6.

Model of NF-E2 and USF mediated assembly and transfer of elongation competent transcription complexes in the β-globin gene locus. Incomplete elongation-incompetent Pol II transcription complexes are first recruited to the LCR. This is mediated in part by USF2, its associated co-factor CBP, TFIIB, and other proteins. After erythroid differentiation expression of NF-E2 (p45) and USF increases and these proteins efficiently associate with the LCR. This leads to the recruitment or assembly of transcriptionally competent Pol II complexes and phosphorylation of the Pol II CTD. The differentiation of erythroid cells is also accompanied by a conformational change in the globin locus that juxtaposes the adult globin gene with the LCR. This facilitates the transfer of elongation-competent transcription complexes from the LCR to the adult globin gene.