Increased γ-globin expression in a nondeletion HPFH mediated by an erythroid-specif ic DNA-binding factor

Abstract

IN man, a shift from γ- to β-globin gene expression in erythrob-lasts underlies a switch from fetal to adult haemoglobin during development¹. In hereditary persistence of fetal haemoglobin (HPFH), inappropriately high γ-globin expression in adult life is associated with deletions in the β-globin cluster or with single-base changes upstream of the γ-globin genes. To account for enhanced γ-gene expression in HPFH of the non-deletion type, we tested the nuclear proteins of human erythroleukaemia cells² that bind γ-promoter sequences in vitro by correlating specific mutations in their binding sites with promoter activity. An eryth-roid-specific factor (GF-1) binds as a single molecule to the –195 to –170 region and contacts two TATCT(AGATA) motifs, but not the conserved octamer (ATGCAAAT)^3–8 that separates them. We observe that a single change (at –175, T→C ) found in HPFH^9,10 leads to increased promoter activity only in erythroid cells. This effect is mediated by GF-1, the human counterpart of the chicken erythroid factor¹¹ Eryf 1. The form of HPFH we studied here is an inherited disorder which can be ascribed to the action of a cell-specific DNA-binding factor on a mutant promoter.