Cells were fixed in 1% formaldehyde for 10 min and cross-linking was quenched by addition of 0.125 M glycine. Cells were then harvested in ChIP buffer and sonicated with a Bioruptor UCD-300 to obtain fragments around 250 bp in size. Precipitated DNA was recovered by purification with a QIAquick PCR purification kit (Qiagen) Libraries for sequencing were obtained using a ChIP-Seq DNA sample prep kit (Illumina) according to the manufacturer's reccomendations