GABPα is the major Ets transcription factor that binds to the proximal αIIb promoter by EMSA. (A) EMSA using nuclear extract from either Y10 cells or NIH3T3 cells. Indicated above the gel is whether a ³²P-labeled 27 bp probe from –53 to –27 bp upstream of the murine αIIb gene transcription start site¹²  (WT) or a similar probe mutated within the core Ets binding motif was included. Indicated below the gel are the antibodies included. αF = anti–Fli-1 antibody. C = isoimmune control antibodies. The fold excess of the cold competitor probe is also indicated. The source of nuclear extracts is indicated at the bottom. The position of migration of Fli-1 is indicated by a thin open arrow. (B) EMSA using WT probe and Y10 nuclear extract. αG1 and αG2 = 2 anti-GABPα antibodies. αGb = anti-GABPβ.C = isoimmune control antibodies. The positions of migration of GABPα and Fli-1 are indicated by a thick black arrow and a thin open arrow, respectively. (C) Competitive binding of GABPα and Fli-1 to the αIIb proximal promoter in vitro. The probe is same as in panel B, but these studies use nuclear extracts from COS cells or COS cells overexpressing HA-Fli-1. The amounts of GABPα and Fli-1 added in each lane are indicated. The position of migration of GABPα and Fli-1 are indicated as in panel B. All gels are representative studies of at least 3 similar studies with similar outcomes.