mESCs were pre-plated to deplete MEF feeders before collection. Cells were fixed with 1% formaldehyde after which chromatin was isolated and sonicated to 150-300 bp using Bioruptor (Diagenode). Sonicated chromatin was precleared with Protein A/G Dynabeads then incubated in antibody overnight. Chromatin was then immunoprecipitated with Protein A/G Dynabeads for > 2 hours. ChIP was washed successively by two rounds of low-salt buffer, two rounds of high-salt buffer, two rounds of LiCl buffer, and finally two rounds of TE buffer. ChIP DNA was eluted in TE, reverse crosslinked overnight, treated with RNase A, then proteinase K, and finally extracted with phenol-chloroform and ethanol precipitation. ChIP-seq libraries were prepared using KAPA Hyper Prep Kit per manufacturer's recommendations. Libraries were quantified using Qubit Fluorometer and Bioanalyzer High Sensitivity DNA Analysis Kit individually. Libraries were pooled and sequenced using the Illumina HiSeq 2000 machine as either 50-bp or 100-bp single-end sequencing reads.