The ChIP protocol was adapted from the Millipore ChIP Assay Kit (17-295) with minor modifications. Cells were washed in PBS and 100 000 000 cells were cross-linked at 37° C for 10 min in 5ml PBS/0.5%BSA/1% ultra-pure formaldehyde(Electron Microscopy Sciences). Quenching with 125mM glycine and a cold PBS wash (containig 1 protease inhibitor cocktail (PIC); Roche) was followed by cell lysis in 5ml of 1% Triton X-100, 50mM MgCl2, 100mM Tris-HCl pH 7.1, 11% sucrose, 1 PIC for 10 min on ice. Nuclei were pelleted and were lysed in 500 ml of 1% SDS, 50mM Tris-HCl, 10mM EDTA, 1 PIC. Chromatin was sonicated to 500–300 bp using a Bioruptor 200 (Diagenode), cleared by centrifugation and sonication efficiency was verified. Libraries were prepared according to standard Illumina protocols and were validated with the Agilent Bioanalyzer