Nuclear protein (20 μg) was preincubated in 20 μL binding buffer containing 10 mM Tris-HCl (PH 7.5), 1 mM MgCl2, 0.5 mM NaCl, 4% glycerol, 0.5 mM EDTA, 0.5 mM DTT, and 2 μg poly dI-dC for 20 minutes on ice.