Briefly, 5-7 x 107 crosslinked cells were resuspended in 10 ml buffer 1 (50 mM HEPES-KOH, pH 7.5, 140 mM NaCl, 1 mM EDTA, 10% glycerol, 0.5% NP-40, 0.25% Triton X-100, 1x Sigma protease inhibitor) and incubated on ice for 10 minutes. Samples were pelleted at 1,350xg for 5 minutes, resuspended in 10 ml buffer 2 (10 mM Tris-HCl, pH 8.0, 200 mM NaCl, 1 mM EDTA, 0.5 mM EGTA, 1x Sigma protease inhibitor) and incubated on ice for 10 minutes. Pelleted samples were resuspended in 2 ml Covaris sonication buffer (10 mM Tris-HCL, pH 8.0, 1 mM EDTA, 0.1% SDS, 1x Sigma protease inhibitor) and sonicated using a Covaris E220 focused ultrasonicator. Samples were diluted with 5 volumes of buffer 3 (10 mM Tris-HCl, pH 8.0, 100 mM NaCl, 1 mM EDTA, 0.5 mM EGTA, 0.1% Na-Deoxycholate, 1% Triton X-100, 1x Sigma protease inhibitor). Chromatin was subjected to ChIP using rabbit polyclonal antibodies. Libraries were prepared according to Illumina's instructions