Cells were cross-linked with 1% (v/v) formaldehyde for 5 minutes at 37℃ and lysed. Then, nuclear pellets were sheared with Focused-ultrasonicator (Covaris) and immunoprecipitated. The immune complexes were eluted by adding 250ul of elution buffer containing 1% (w/v) SDS and 0.1M NaHCO3 two times. Cross-linking was reversed by adding of 20ul of 5M NaCl and incubated overnight at 65C. DNA was precipitated with ethanol and kept in -20℃ for the further use. The immunoprecipitated (20ng/μL) samples were used for library preparation for Illumina sequencing using the TruSeq ChIP kit (Illumina, San Diego, CA) following the manufacturer's protocol. Briefly, 20 ng of immunoprecipitated DNA samples was end repaired-ligated to Illumina adaptors and selected for a fragment size of approximately 300 bp by gel extraction. Multiplex Illumina primers were used to amplify gel-extracted products.