Main Regulated DNA accessibility governs cell-type-specific transcription. DNA accessibility revolves around the octameric nucleosome, which compacts approximately 147 base pairs (bp) of DNA around two dimers of histone proteins H2A and H2B flanking a tetramer of histone proteins H3 and H4. Our canonical understanding of how chromatin accessibility regulates nuclear function is simple: nucleosomes and positive transcriptional regulatory factors compete for DNA binding, particularly at active cis -regulatory elements 1 . Nucleosome occupancy negatively regulates transcription, and essential coactivators modulate nucleosome occupancy through chromatin remodelling. Work over the past three decades has challenged this simple model.…