Binding of GATA-1 and CP2 to the GATA-1 HS2 enhancer element. (A) Studies of recombinant GATA-1 and CP2 confirm that both proteins bind to the HS2 enhancer element. Note that antibody against GATA-1 supershifts both the GATA-1 and the GATA-1-plus-CP2 bands (lanes 5 and 7, asterisks). The positions of the GATA-1, CP2, and GATA-1-plus-CP2 complexes are indicated. (B) Western analysis of extracts from primary fetal liver cells from E12.5 day embryos (FL E 12.5) and immortalized mouse yolk sac (YS Epo) and bone marrow (ts Epo) growth factor-dependent cell lines with anti-CP2 antibody. Anti-OCT-1 antibody served as the loading control. (C) The GATA-1-plus-CP2 band was obtained using extracts from various hematopoietic cell types (lanes 1 to 3); compare lanes 1 to 3 with lanes 4 to 6, where the anti-CP2 antibody was added. Recombinant CP2 added to nuclear extracts from the same hematopoietic cell extracts generates a strong GATA-1-plus-CP2 band (lanes 7 to 9); compare lanes 7 to 9 with lane 10, K562 nuclear extracts.