RUNX1/CBFβ and C/EBP factors compete for binding to the MS7 element. (A) EMSA was performed on a limiting amount of MS7 (left and center panels) or MS7 + 10 (right panel) oligonucleotide probes using nuclear extracts from COS-7 cells transfected with either RUNX1/CBFβ and C/EBPα42 (left panel) or with RUNX2/CBFβ and C/EBPα30 (center and right panels). Binding reactions were carried out using a constant amount of RUNX/CBFβ-transfected cells and increasing amounts of extracts from C/EBPα-transfected cells. The sequence of MS7 and MS7 + 10 is indicated. (B) Identification of factors in ternary complexes. EMSA was performed on a limiting amount of MS7 (left panel) or MS7 + 10 (right panel) oligonucleotide probes using equal amounts of nuclear extracts from COS-7 cells transfected with either RUNX2/CBFβ or C/EBPα30. Where indicated, unlabeled competitor oligonucleotides (MS7, MS7mutRUNX, or MS7mutCEBP) were added at 100-fold molar excess. In all cases, the position of RUNX/CBFβ- and C/EBP-containing complexes is indicated.