library_construction_protocol: After antibody Immunoprecipitation, target DNA was eluted from Dynabeads and precipitated using ethanol followed by twice washes, finally the samples was dried and dissolved in 33 μl ddH2O Qualified library for sequencing was prepared using the QIAquick PCR Purification Kit(Qiagen). Briefly, 10-300ng DNA was taken to do DNA-end repair(3'-dA overhang and ligation of methylated sequencing adaptors) followed by PCR amplication and size selection (usually 100-300bp, including adaptor sequencing).