Crosslinked chromatin was fragmented by sonication with the Bioruptor sonicator (Diagenode) to achieve fragment sizes of ~200–500 base pairs using the following sonication buffer: 10mM Tris-HCl pH 8.0, 100mM NaCl, 1mM EDTA pH 8.0, 0.5mM EGTA pH 8.0, 0.1% Na-Deoxycholate, 0.5% N-lauroylsarcosine. ChIP-seq libraries were constructed starting from 4ng of ChIP or Input DNA as reported in Blecher-Gonen et al., 2013, Nature protocol. Libraries were quantified using the KAPA SYBR FAST Universal qPCR Kit (KAPA Biosystems), normalized to 10nM, pooled and sequenced in an Illumina HiSeq 2500 instrument as single-end 101 bp reads.