Growth media was removed and MEFs were crosslinked in 1% formaldehyde for 10 minutes at room temperature before quenching with glycine at a final concentration of 0.125M. Sonicated chromatin from isolated nuclei were used as input to ChIP. 2-40 ng of each ChIP sample was used to prepare ChIP-Seq libraries with the NuGEN Ovation Ultralow Library System v2 kit.