Cells were fixed with 1% formaldehyde for 15 min and quenched with 0.125 M glycine. Lysates were sonicated with a microtip sonicator to shear the DNA. Genomic DNA (Input) was prepared by treating aliquots of chromatin with RNase, proteinase K and heat for de-crosslinking, followed by ethanol precipitation. Starting with 50 ug of chromatin, genomic DNA regions of interest were isolated using Flag-M2 affinity beads. Immune complexes were washed, eluted from the beads with SDS buffer, and subjected to RNase and proteinase K treatment. Crosslinks were reversed by incubation overnight at 65 C, and ChIP DNA was purified by phenol-chloroform extraction and ethanol precipitation. Illumina sequencing libraries were prepared from the ChIP and Input DNAs by the standard consecutive enzymatic steps of end-polishing, dA-addition, and adaptor ligation. After a final PCR amplification step, the resulting DNA libraries were quantified and sequenced on HiSeq 2500.