Chromatin immunoprecipitation was performed as described (Kadauke et al. Cell 2012). Cells were fixed in 1% formaldehyde for 10 minutes with gentle shaking at room temperature. Sonication employed a Diagenode Bioruptor (High signal, 30 seconds on/30 seconds off, for 30 minutes). IPs were performed using protein A/G sepharose beads. Beads were washed in high salt buffer and eluted in buffer containing bicarbonate and SDS. Crosslinks were reversed by heating to 65 degrees overnight. DNA was purified on Qiagen miniprep columns. Libraries were prepared using the protocol as outlined for Illumina's TruSeq ChIP Sample Prep Kit ( IP-202-1012), except that the libraries were size selected using Agencourt SPRIselect beads for an average size of ~300-325bp prior to PCR amplification. Library quality was assessed using the Aglient Bioanalzyer 2100 and libraries were sequenced on the Illumina HiSeq2000.