For native ChIP-seq, 5 x 10^7 mouse ESCs (both untreated and following RA treatment) were collected and washed once in PBS. Cells were pelleted and nuclei were released by resuspending in ice cold lysis buffer (10mM Tris-HCl pH 8.0, 10 mM NaCl, 3 mM MgCl2, 0.1% NP40, 5 mM N-ethylmaleimide). Nuclei were then washed, and resuspended in 1 ml of MNase digestion buffer (10 mM Tris-HCl pH 8.0, 10 mM NaCl, 3 mM MgCl2, 0.1% NP40, 0.25M sucrose, 3mM CaCl2, 10 mM N-ethylmaleimide, 1x protease inhibitors (Sigma)). Each sample was then incubated with 200 units of MNase (Fermentas) at 37°C for 5 min, followed by the addition of 4 mM EDTA to halt MNase digestion. Following centrifugation at 1500 g for 5 min at 4°C, the supernatant (S1) was retained. The remaining pellet was incubated with 300 µl of nucleosome release buffer (10 mM Tris-HCl pH 7.5, 10 mM NaCl, 0.2 mM EDTA, 1x protease inhibitors, 10 mM N-ethylmaleimide) at 4°C for 1 h, passed five times through a 27G needle using a 1 ml syringe, and spun at 1500 g for 5 min at 4°C. The second supernatant (S2) was collected and combined with corresponding S1 sample from above. A small amount of S1/S2 DNA was purified and visualized on a 1.5% agarose gel to confirm digestion to mostly mono-nucleosomes. Libraries for both ChIP and Input samples were prepared using NEBNext Ultra II DNA Library Prep Kit for Illumina (NEB #E7103), following manufacturer's guidelines. Samples were indexed using NEBNext Multiplex Oligos. The average size and concentration of all libraries was analysed using the 2100 Bioanalyzer High Sensitivity DNA Kit (Agilent) followed by qPCR using SensiMix SYBR (Bioline, UK) and KAPA Illumina DNA standards (Roche). Libraries were sequenced as 40 bp paired-end reads on Illumina NextSeq 500 platform in biological quadruplicate.