Crosslinked with 1% formaldehyde, washed with PBS, lysed in lysis buffer (1% SDS, 10mM EDTA, 50mM Tris-HCl, pH 8.0), sonicated with Covaris E210 to shear DNA to 200-1500bp. After immunoprecipitation or without immunoprecipitation for input, beads were washed, RNase A and Proteinase K treated and reverse crosslinked in elution buffer (1% SDS, 0.1M NaHCO3). DNAs were column purified and subjected to standard Illumina library construction.