For EMSA, 5 µg of nuclear proteins were preincubated on ice with 2 µg of poly(dI-dC) (Roche) as an unspecific competitor and 1 µg of bovine serum albumin in band shift buffer (50 mM Tris, 150 mM KCl, 5 mM EDTA, 2.5 mM dithiothreitol, 20% Ficoll) for 15 min.