αTC1-9 cells in culture dishes were cross-linked with 1% formaldehyde for 10 minutes, processed for chromatin lysate preparation and chromatin immunoprecipitation (ChIP). Chromatin lysate was sonicated with a Bioruptor system (Diagenode) to yield a DNA smear averaging ~200-500 bp. Sonicated chromatin lysate from 5 million ES cells was used for each ChIP with ANTI-FLAG® M2 Affinity Gel. Input and ChIP DNA were size-selected (~200-500nt). Libraries were prepared from size-selected Input and ChIP DNA according to the standard Illimina library preparation protocol