GABPα as well as Fli-1 mediates GATA-1/FOG-1 synergy at the αIIb promoter. (A) Schematic representations of the preserved domains of GABPα (top) and of the vector system used in the assay (bottom). The reporter construct contained 100 bp of αIIb promoter region in which a GAL4-binding site was substituted for the Ets-binding site. GAL4 fusion constructs of 3 different Ets transcription factors, Fli-1, GABPα, and PU.1, were coexpressed with GATA-1 and FOG-1 as indicated in panel B. (B) Transient expression studies done in NIH3T3 cells with the modified 100-bp αIIb promoter reporter construct ± GATA-1 ± FOG-1 in the presence of the indicated recombinant protein at the bottom. The mean ± one SD of 3 experiments, each in triplicate, is shown.