The cells(>5×10^6) were treated with formaldehyde to 1% final concentration followed by incubation for 10 min at 37ºC.Cells  were resuspended in 100 µl lysis buffer (containing 0.3% SDS) plus protease inhibitors.The lysate is sonicated to shear the crosslinked DNA to lengths between 200 and 500 bp. The lysate was incubated with corresponding antibody overnight. Histone-DNA complex were isolated and reverse crosslinked overnight.DNA was extracted to build a library. DNA was end-repaired, adenylated and ligated to TruSeq sequencing adapters. After purification with DNA clean beads (Vazyme), DNA was amplified by Phusion High-Fidelity DNA Polymerase (catalog no. M0530L; New England Biolabs) or Pfu Turbo Cx Hotstart DNA polymerase (for bisulfite-treated DNA libraries). The amplified DNA was size-selected using  DNA clean beads for 200 to 500-bp DNA fragments. All libraries were sequenced using an Illumina HiSeq 2500 system according to the manufacturer's instructions.