Cells were fixed in 1% formaldehyde (648336, Polysciences) at room temperature for 10 min and then quenched in 100 mM glycine for 1 min. Cells were washed twice in PBS and lysed 15 min in 50 mM Tris-HCl ph8.1/10 mM EDTA/0.5% Empigen BB/1% SDS. Lysates were clarified from sonicated nuclei and histone-DNA complexes were isolated with antibody. ChIP-seq libraries were generated using TruSeq® ChIP Library Preparation Kit (Illumina) according to the manufacturer's protocol.