To isolate pre-cancerous epidermal cells following short DMBA/TPA treatment, back skins were dissected and processed to singlecell suspensions as previously described (Jensen et al. 2010). For ChIP-seq, single-cell suspensions were cross-linked for 10 min at room temperature with 1% formaldehyde (methanol-free; Thermofisher, 28906) and quenched for 5 min to a final concentration of 0.125M glycine. Cells were washed 2x with cold PBS and frozen at -80°C. Libraries for sequencing were prepared using NEBNext Ultra DNA Library Prep Kit from Illumina (E7370L) following the manufacturer's instructions.