Biologically active nuclear extract preparation. Cells were treated with 50 ng/mL phorbol 12-myristate 13-acetate for 2 hours at 37oC. Nuclei were isolated and then lysed in nuclear extraction buffer (20 mM HEPES, pH 7.9, 1.5 mM MgCl2, 0.42 M NaCl, 0.2 mM EDTA, 1% IGEPAL CA-630, 25% glycerol, and protease inhibitor cocktail). Protein concentration was determined and then normalized to 2.5 mg/mL.