preB-ALL cells were crosslinked with formaldehyde solution. Nuclei were isolated as previously described and sonicated in lysis buffer. DNA was purified with phenol-chloroform extraction and ethanol precipitation. Purified ChIP DNA was used to prepare Illumina multiplexed sequencing libraries. Libraries were prepared following the TruSeq DNA Sample Prep v2 Kit (Illumina). Amplified libraries were size-selected using a 2% gel cassette in the Pippin Prep system (Sage Science) set to capture fragments between 200-400 bp. Libraries were quantified by qPCR using the Illumina Library Quantification Kit (KAPA Biosystems) according to manufacturer guidelines. Libraries were sequenced on the Illumina HiSeq2500 for 40-nt in single read mode.