An erythroid specific nuclear factor binding to the proximal CACCC box of the β-globin gene promoter

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Abstract
We have used the gel retardation and DNAse I assays to investigate the binding of nuclear proteins to the human .beta.-globin promoter. Upon incubation with .beta.-globin promoter fragments containing the duplicated CACCC boxes, nuclear proteins from human erythroid cells generate complexes yielding four retarded bands in acrylamide gels; the three slowest bands are common to both erythroid and non erythroid cells. The fast band is present only in K562 erythroleukemic cells induced to differentiation and hemoglobin accumulation and in fetal and adult erythroblasts, but absent in uninduced K562 cells. Binding occurs on a short DNA region including the proximal CACCC box, and is not significantly competed by excess .gamma.-globin fragments containing the CACCC box; the CACCC box appears to be essential for this binding, as shown by the failure of a fragment containing a natural .beta.-thalassemic mutation (-87, C >) to bind significantly to nuclear factors. These data suggest that the erythroid specific CACCC binding factor might play a role in the developmental activation of .beta.-globin transcription.