~2x10^7 cells were lysed using digesting buffer (50 mM Tris-HCl pH 7.6, 1 mM CaCl2 and 0.2% Triton X-100) and digested with micrococcal nuclease to obtain mono-nucleosomes. The chromatin were then dialyzed into RIPA buffer (10 mM Tris pH 7.6, 1 mM EDTA, 0.1% SDS, 0.1% Na-Deoxycholate, 1% Triton X-100) for 2 h at 4°C. After centrifugation, soluble chromatin was incubated with 3-5 μg of antibody bound to 75 μl protein A or protein G Dynal magnetic beads (Invitrogen) and incubated overnight at 4°C, with 5% kept as input DNA. Magnetic beads were washed with RIPA buffer and LiCl buffer (0.25 M LiCl, 0.5% NP40, 0.5% Na-Deoxycholate) and chromatin was eluted. ChIP DNA was treated with Proteinase K (Roche) and recovered using Qiagen PCR purification kit. libraries were prepared according to the Illumina TruSeq protocol