Chromatin immunoprecipitation was performed as previously described (Frank et al., 2001) with some modification. Briefly, LCL were centrifuged at 150g for 5 minutes, an average of 150 x 106 LCLs were re-suspended in formaldehyde 1% in PBS for cross-linking. To stop the cross-linking reaction glycine was added to the final concentration 125 mM. Cells were re-suspended using ChIP SDS buffer (0.5% SDS, 5 mM EDTA, NaCl 100mM and 50 mM Tris-HCl at pH 8.1). Pellets were collected by centrifuging at 400g for 30 min and re-suspended in IP buffer (0.5% SDS, 5 mM EDTA, NaCl 100mM and 50 mM Tris-HCl at pH 8.6, Triton X-100 1,5%). To obtain a bulk of 300 bp DNA fragments, cells were sonicated using the Branson digital sonifier (Emerson Industrial Automation). Chromatin was quantified using Bradford protein assay (Bio-Rad). To immuno-precipitate YY1, 1 mg of total proteins was incubated with YY1 antibodies (sc-1703 or sc-281, Santa-Cruz Biotechnologies). For H3K27Ac chromatin immunoprecipitation, 100µg of proteins were immuno-precipitated using the antibody ab4729 (Abcam). Chromatin was incubated overnight with antibody at 4°C. G-Sepharose 4B (Thermo Fisher) beads were incubated with chromatin and antibodies mix for 4 hours at 4°C and followed by washes using low and high salt buffers (1% Triton X-100, 0.1% SDS, 150mM or 500mM NaCl , 2mM EDTA, 20 mM Tris-HCl ph8). Decross-linking was performed at 65°C for 3 hours. DNA was collected with QIAquick PCR Purification Kit (Qiagen). Libraries were prepared as already described (Blecher-Gonen et al., 2013) with adaptations for the automated system Biomek FX.