After reaching ~80% confluency, ChIP was performed by cross-linking proteins to DNA using 1% formaldehyde solution (neutralized with 125 mM glycine) J1 mouse ES cells. After sonication and extensive washing, immunoprecipitated DNA was sequenced using Illumina sequencers. After pulldown, DNA was used to generate sequencing libraries using the NEBNext® Ultra™ II DNA Library Prep Kit for Illumina® (#E7645S) according to the manufacturer's instructions.