library_construction_protocol: Lysates were clarified from sonicated nuclei and protein-DNA complexes were isolated with corresponding antibodies. Libraries were prepared according to manufacturer's protocol of  the Ovation Ultralow System V2 1-16 Kit (NuGEN Technologies).  Briefly, the DNA was end-repaired and ligated to Illumina sequencing adaptors. The ligated DNA was purified using Agencourt RNAClean XP beads (Beckman Coulter). A subsequent PCR amplification step (8-15 cycles) was performed to add linker sequence to the purified fragments for annealing to the Genome Analyzer flow-cell. Following PCR amplification, the library was separated on a 2% agarose gel (120 V, 1.5 hours) to select a narrow range of fragment sizes, and bands between 200-500 bp were excised. The library was purified from the excised agarose gel using the Qiagen MiniElute PCR Purification Kit following the manufacturer's protocol.