Differentiated ES cells were disassociated into single cells and lysed. Chromatin was crosslinked for 10 min at room temperature with 1% formaldehyde, and then sonicated to ~100-250bp using an AFA Focused-ultrasonicator. After sonication, chromatin was immunoprecipitated with V5 or ER71 antibodies at 4C overnight. The reversed ChIP DNA was purified using Qiagen MinElute columns and eluted in 16 μl EB (Qiagen), and then quantified with Qubit. ChIP DNA was blunt ended, had addition of “A” base to 3’ end, and had sequencing adapters ligated to the ends. The fragments were size selected to 200-600 base pairs, and underwent amplification for 15 cycles.