Chromatin was cross-linked with 1% formaldehyde for 10 min, followed by quenching with 0.125 M glycine for 5 min. Cells were washed and incubated in swelling buffer (10 mM HEPES pH 7.8, 1.5 mM MgCl2, 10 mM KCl, 0.1% NP-40, 1 mM DTT, 0.5 mM PMSF) for 15 min on ice, followed by nuclei isolation by dounce homogenization. Nuclei were pelleted and resuspended in RIPA buffer (1% NP-40, 0.5% sodium deoxycholate, 1% SDS in PBS pH 7.4), and chromatin was sheared with a Vibra-Cell Sonicator VC130 (Sonics) six times for 30 sec at 60% amplitude. Single end libraries were generated according to the manufacturer’s instructions (Illumina).