BJ-5ta fibroblasts were fixed in 1% paraformaldehyde for 8 min. Formaldehyde fixation was quenched by adding glycine (final concentration, 0.125 M) and ChIP was performed using the iDeal ChIP-seq kit (Diagenode, Liege, Belgium) according to the manufacturer's instructions. Chromatin extracts from one million cells were sonicated to yield 100 to 500 bp fragments using a Bioruptor Pico sonication device (Diagenode) set on high power for one round of 10 cycles with 30 seconds on and 30 seconds off at 4 °C. Fragmentation was verified after library preparation with agarose gel electrophoresis using an Agilent Tapestation 2200 machine and software (Agilent, Sundbyberg, Sweden) to carry out a high sensitivity D1000 analysis (Supplementary Figure 3). Spike-in Chromatin (Active Motif), was added in an amount of 10ng to each sample