Identification of the +48/+80 binding activity as NFY. Binding reactions were performed in the absence (lane 1) or presence of 20 μg of nuclear extract from KG1a (lanes 2 to 12), RPMI-8402 (lanes 13 to 16), Jurkat (lanes 17 to 19), HeLa (lanes 20 to 22), and CD34⁺ peripheral blood cells cultured with G-CSF for 22 days (75% CD15⁺; lanes 23 and 24). The unlabeled competitors were as follows: self-competitor in lane 3; oligonucleotide −78/−28 from the murine CD34 promoter in lane 4; 5′ untranslated region from the murine CD34 (base pairs +48/+119) in lane 5; NFY binding site from the human CD10 promoter41 in lanes 6, 15, 18, 21, and 24; NF1 binding site41 in lane 7; C/EBP consensus oligonucleotide61 in lane 14. The reactions in lanes 8, 16, 19, and 22 included anti-NFYA antibodies provided by Benoit de Crombrugghe.28 Lanes 10 and 11 contained, respectively, anti-NFYA and anti-NFYB antibodies supplied by Roberto Mantovani.29 Supershifted complexes (s.s.) as well as free probe are indicated by arrows.