ChIP experiments were performed using 15 µg anti-HA antibody for 3~4X107 cells according to standard protocols. Crosslinking of the cells was performed with 1% PFA for 10 minutesDisuccinimidyl glutarate crosslinker (COVAChem) at final concentration of 2 µM at room temperate for 30 min and 1% paraformaldehyde (Sigma) at room temperature at 10 min. ChIPed DNA was purified by Qiaquick PCR purification Kit (Qiagen). Libraries were prepared with the Illumina TruSeq protocol according to the manufacturer's protocol.