~2x10^7 cells were fixed with 1% formaldehyde for 10 min at room temperature and then quenched with 125 mM glycine for 5 min. Cells were then lysed in SDS lysis buffer (1% SDS, 10 mM EDTA, 50 mM Tris-HCl) and sonicated for 1 h with Bioruptor (Diagenode) to obtain mononucleosomes. After centrifugation, the lysates were diluted with dilution buffer (167 mM NaCl, 0.01% SDS, 1.1% TritonX-100, 1.2 mM EDTA, 16.7 mM Tris-HCl) and incubated with αCbx2 (Active Motif, 39663) antibody bound to 75 μl protein A Dynal magnetic beads (Invitrogen) and incubated overnight at 4°C, with 5% kept as input DNA. Magnetic beads were washed with low salt buffer (150 mM NaCl; 0.1% SDS; 1% Triton X-100; 1 mM EDTA; 50 mM Tris-HCl), high salt buffer (500 mM NaCl; 0.1% SDS; 1% Triton X-100; 1 mM EDTA; 50 mM Tris-HCl), LiCl buffer (150 mM LiCl; 0.5% Na deoxycholate; 0.1% SDS; 1% Nonidet P-40; 1 mM EDTA; 50 mM Tris-HCl) and TE buffer (1 mM EDTA; 10 mM Tris-HCl). ChIP DNA was eluted, treated with Proteinase K (Roche) and recovered using Qiagen PCR purification kit. libraries were prepared according to the Illumina TruSeq protocol