Constitutive SP1 and SP3 binding to the chromatin embedded MAD1 promoter. A. Nuclear extracts of U937 cells were incubated with radiolabelled GC box1 and supershift experiments were performed with SP1 (α-SP1-1, SC-59; α-SP1-2, obtained from G. Suske) and SP3 specific antibodies. The EMSA was performed as described in the legend to Figure 3. B. Schematic representation of the positions of primer sets used for ChIP PCR relative to the major transcriptional start site within the MAD1 gene (upper panel). U937 cells were treated with 2.5 ng/ml TGFβ1 for 1.5 h, cross-linked and examined for SP1 and SP3 binding by ChIP. The isolated DNA was analyzed by PCR using the indicated primer sets.