FIG. 1.

Binding of CP2 to the GATA-1 HS2 enhancer element. (A) EMSA using an oligonucleotide (positions −718 to −655) encompassing the GATA-1 CP2 binding motifs present in the HS2 enhancer with K562 cell nuclear extract. The effects of excess unlabeled GATA-1 binding (globin GATA-1) and CP2 binding (SSE) competitors are shown. The positions of the GATA-1, CP2, and GATA-1-plus-CP2 complexes are indicated. Note that both competitors abolish the upper band, demonstrating that it contains both CP2 and GATA-1. (B) Unlabeled oligonucleotides comprising the wild-type (wt) or mutated GATA-1 palindrome do not affect the binding of CP2 to the GATA-1 HS2 enhancer oligonucleotide in competition experiments. Note that the weak GATA-1 binding mutant (5′ mut GATA-1, lanes 3 to 4) competes almost completely for the GATA-1 band, while it leaves the upper CP2-plus-GATA-1 band essentially intact. A specific anti-CP2 antibody, but not an anti-NF-E4 antibody, abolishes the CP2 band (lanes 10 to 11). The positions of the GATA-1, CP2, and GATA-1-plus-CP2 complexes are indicated. (C) Schematic representation of the GATA-1 and CP2 binding sites on the mouse GATA-1 promoter.