Cells were crosslinked by formaldehyde and lysated by SDS lysis buffer. Sonicated nuclei were incubated with antibody overnight and then pulled down by dynabeads. After washing, decrosslinking was performed to isolate DNA. Libraries were generated by the NEBNext® Ultra II DNA Library Prep Kit (New England Biolabs; E7103S) and NEBNext® Multiplex Oligos for Illumina® (New England Biolabs Index Primers Set 1; NEB, E7335S). Samples were QC on a Bioanalyzer(Agilent) and sequenced on an Illumina Next Gen sequencer by the Integrated Genomic Operation(IGO) Core Facility at the MSKCC.