After cross-link, cells were incubated with cell lysis buffer (10mM Tris pH8.0, 10mM NaCl, 0.2% NP-40) and then resuspended and sonicated in nuclei lysis buffer (50mM Tris pH8.0, 10mM EDTA, 1%SDS) for 15mins, followed by ChIP Library was constructed using Illumina TruSeq ChIP Sample Prep kit following manufacture’s protocol. Briefly, ChIP DNA was end repaired, followed by A tailing and size selection (250-500 bp) by gel electrophoresis. 15 PCR cycles were used for final library amplification and the library was analyzed on Bioanalyzer using high sensitivity DNA chip (Agilent) on Bio-analyzer.