To isolate chromatin, formaldehyde-cross-linked nuclei were sonicated using a Covaris focused-ultrasonicator. Following ChIP performed with specific antibodies and Dynabeads® Protein G (Invitrogen) ChIP DNA was subjected to end repair, A-tailing, ligation of Illumia single end adaptor. Following PCR amplification for 18 cycles, the final library underwent gel purification.