library_construction_protocol: 10^7 mES cells were crosslinked, chromatin was extracted and sonicated to an average size of 300bp. 5% of chromatin was set aside as Input control. The chromatin was incubated with antibody and protein A/G coupled Dynabeads, washed and de-crosslinked. Purified DNA was subsequently used for library preparation. For a detailed protocol, see Kaaij et al, 2019. Libraries were prepared using the NEB Next Ultra II DNA library prep kit according to manufacturers instructions.