Cells were fixed in 1% formaldehyde, washed, snap frozen, and stored at -80ºC. Sonication of crosslinked cells was calibrated such that DNA was sheared to between 300bp and 2000bp. ChIP DNA was used to generate sequencing libraries by end repair (End-It DNA repair kit, Epicentre), 3' A base overhang addition via Klenow fragment (NEB), and ligation of barcoded sequencing adapters.