immunoprecipitated DNA was end-repaired, A-tailed, ligated to the sequencing adapters, amplified by 18 cycles of PCR and size selected (200-300 bp) followed by single end 4 sequencing on an Illumina Genome Analyzer according to the manufacturer’s recommendationas described in Chandra, T. et al. Independence of Repressive Histone Marks and ChromatinCompaction during Senescent Heterochromatic Layer Formation. Mol Cell 47, 203–214 (2012)