ChIP-seq libraries were prepared using ChIP-Seq Sample Prep Kit (#IP-102-1001, Illumina) following the manufacturer's protocol with some modifications. Briefly, 10 ng of ChIP enriched DNA or control DNA were end repaired using T4 DNA polymerase, Klenow DNA polymerase and T4 PNK. A single ‘A’ nucleotide was added to the 3’ ends of the blunt DNA fragments with a Klenow fragment (3' to 5'exo minus). The ends of the DNA fragments were ligated to double stranded adapters using T4 DNA Ligase. The ligated products were enriched by PCR (30 sec at 98°C; [10 sec at 98°C, 30 sec at 65°C, 30 sec at 72°C] x 14 cycles; 5 min at 72°C) and then purified using Agencourt AMPure XP beads (#A63881, Beckman). DNA library size selection was performed by excising the 250-350 bp fragments from a 2% agarose gel followed by purification using a QIAquick Gel Extraction Kit (#28906, Qiagen).