cells were fixed with 1% Formaldehyde for 10 minutes, then quenched with 0.125M Glycine. After nuclei extraction as described in Rada et al, Nature 2011. Sonication was carried out using Diagenode bioruptor in 15ml Falcon tubes. Each ChIP was validated using q-PCR against selected loci. libraries were prepared for Illumina sequencing using descibed protocols. All libraries were sequenced as single reads, 36bp length on the Illumina Genome Analyzer Iix.