Cells were fixed with 1% formaldehyde. After wash with PBS, the cells were lyzed in ChIP lysis buffer. Lysates were sonicated and cleared by centrifugation. After pre-clear with protein A beads, HA antibody (ab9100, Abcam) was incubated with the lysate overnight at 40C. Protein A was used to capture the protein DNA complexed. The eluted protein0DNA complexes were reverse crosslinked and DNA was purified by a Qiagen PCR purification column. Libraries were prepared using PrepX BeadX kit from IntegenX. Briefly, DNA was end-repaired. 3' A base was added and ligated to adaptors. After PCR amplification, DNA was purified and analyzed with Illumina HiSeq.