The molecular mechanisms responsible for the human fetal-to-adult hemoglobin switch have not yet been elucidated. Point mutations identified in the promoter regions of ϒ-globin genes from individuals ...with nondeletion hereditary persistence of fetal hemoglobin (HPFH) may mark cis-acting sequences important for this switch, and the trans-acting factors which interact with these sequences may be integral parts in the puzzle of ϒ-globin gene regulation. We have used gel retardation and footprinting strategies to define nuclear proteins which bind to the normal ϒ-globin promoter and to determine the effect of HPFH mutations on the binding of a subset of these proteins. We have identified five proteins in human erythroleukemia cells (K562 and HEL) which bind to the proximal promoter region of the normal ϒ-globin gene. One factor, ϒCAAT, binds the duplicated CCAAT box sequences; the -117 HPFH mutation increases the affinity of interaction between ϒ CAAT and its cognate site. Two proteins, ϒCAC
1
and ϒCAC
2
, bind the CACCC sequence. These proteins require divalent cations for binding. The -175 HPFH mutation interferes with the binding of a fourth protein, ϒOBP, which binds an octamer sequence (ATGCAAAT) in the normal ϒ-globin promoter. The HPFH phenotype of the -175 mutation indicates that the octamer-binding protein may play a negative regulatory role in this setting. A fifth protein, EFϒa, binds to sequences which overlap the octamer-binding site. The erythroid-specific distribution of EFϒa and its close approximation to an apparent repressor-binding site suggest that it may be important in ϒ-globin regulation.
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