Sp1/Sp3 binding to the factor X promoter is required for the maximal promoter activity.

(A) Reporter constructs (2 μg each) containing mutations that disrupt Sp1/Sp3 binding at site 1, site 3, and site 4 (m1, m3, and m4) were transfected into HepG2 cells and compared to the wild-type. m1 + 3, m1 + 4, m3 + 4, and m1 + 3 + 4 contain simultaneous mutations. (B) Reporter constructs (1 μg each) were co-transfected with 1 μg pPac Sp1 or pPacSp3 into Drosophila SL2 cells. Fold increases indicate activities over co-transfection with pPac empty vector (−). Results represent averages of 4 independent transfections.