ChIP assays were performed using a SimpleChIP Enzymatic Chromatin IP kit (Cell Signaling, Cat#9003) based on the manufacturer's instructions. The libraries were prepared using the NEBNext Ultra II DNA Library Prep Kit for Illumina (NEB #E7645S/#E7103S), according to the manufacturer's instructions. Library construction protocol & strategy: (1) The DNA fragments are repaired, dA-tailed. (2) The DNA fragments with A tail are ligated to sequencing adaptors. (3) The final DNA library is obtained by size selection and PCR amplification.