Cells were cross-linked with 1% formaldehyde for 10 min at room temperature and formaldehyde was then inactivated by the addition of 125 mM glycine for 5min. Sonicated DNA fragments with 100–300 bp were pre-cleared and then immunoprecipitated with Protein A+G Magnetic beads coupled with Anti-YY1 antibody (61779, active motif). After reverse crosslinking, immunoprecipitated DNAs and input DNAs were end-repaired and ligated adapters to the DNA fragments.