Cells were washed in PBS and fixed for 10 min in 1% formaldehyde. Fixation was stopped by incubation with 140 mM glycine for 5 min and cells were washed in PBS. Cell pellet was resuspended in fivefold pellet volume of hypotonic buffer (20 mM HEPES pH 7,9, 10 mM KCl, 10% Glycerol, 1 mM EDTA, 0.2% NP-40) and after 4 min centrifuged. Nuclei pellet was lysed in 350 µl ChIP lysis buffer (1% SDS, 10 mM EDTA, 50 mM Tris pH 8,1, protease inhibitor cocktail) for 25 min on ice and subsequently DNA was shared by sonification (6 pulses, 50% amplitude, 30 sec pause in between) using a Branson digital sonifier W-250. By 15 min centrifugation at 15 000 rpm and 4 °C cell debris were removed. 150 µl of the supernatant were diluted with 1350 µl ChIP dilution buffer (0.01% SDS, 1,1% TritonX-100, 1,2 mM EDTA, 16,7 mM Tris-HCL pH 8,1, 167 mM NaCl) and subjected to 2 µg antibody or IgG control at 4 °C overnight. Libraries were prepared with TruSeq ChIP Library Preparation Kit. Bead-based size selection was performed after TrueSeq to enrich for fragments of 550bp.