An erythroid-enriched complex binds a distal element of the HBA promoter. (A) Structure of the HBA core and distal promoter elements. The TSS is depicted as an angled arrow, and the locations of the EMSA probes are shown as gray bars. In vivo dimethyl-sulfate (DMS) footprints detected in K562 and erythroblasts²⁶ are represented by the purple boxes. The nucleotide located 18 bp downstream of the TATA box (*) differs between the HBA1 (C) and HBA2 (G) promoters. (B) EMSA and supershift assays using K562 and EBV nuclear extracts with the indicated probes. (C) The fast-migrating species with probe 13/14 (species d) is enriched in erythroid cells. (D) Sp/X-KLF-family antibodies cause retardation or disruption of the bands (a), (b), and (c), but not (d).