Nuclear protein-binding sites in a transcriptional control region of the rabbit α-globin gene

The 5'-flanking and internal regions of the rabbit α-globin gene, which constitute a CpG island, are required for enhancer-independent expression in transfected cells. In this study, electrophoretic mobility shift assays revealed that a battery of nuclear proteins from both erythroid and nonerythroid cells bind specifically to these regulatory regions. Assays based on exonuclease III digestion, methylation interference, and DNase I footprinting identified sequences bound by proteins in crude nuclear extracts and by purified transcription factor Sp1. In the 5' flank, recognition sites for the transcription factors α-IRP (positions -53 to -44 relative to the cap site), CP1 (-73 to -69), and Sp1 (-95 to -90) are bound by proteins in K562 cell nuclear extracts, as are three extended upstream regions. Two recognition sites for Sp1 in intron 1 are also bound both by proteins in crude nuclear extracts and by purified Sp1. The sequences CCAC in intron 2 and C₅ in the 3'-untranslated region also bind proteins. A major binding site found in exon 1, TATGGCGC, matches in sequence and methylation interference pattern the binding site for nuclear protein YY1, and binding is inhibited through competition by YY1-specific oligonucleotides. The protein- binding sites flanking and internal to the rabbit α-globin gene may form an extended promoter.