FIG. 8.

Model for β-globin gene regulation by helix-loop-helix proteins USF and TFII-I. The β-globin promoter consists of a TATA-like sequence (CATA) located 25 bp upstream of the transcription start site, an initiator with an overlapping E-box, and a downstream E-box element located at +60. We propose that a protein complex containing TFII-I, HDAC3, and possibly other proteins interacts with the β-globin promoter in embryonic and fetal erythroid cells. The modification of histones by HDAC3 confers or maintains inaccessibility of the globin gene to the transcription complex. In adult cells, USF interacts with the β-globin promoter and recruits coactivator complexes that modify the chromatin structure to increase accessibility for transcription complexes.