Abstract
Binding of transcription factors (TFs) at gene regulatory elements controls cellular epigenetic state and gene expression. Current genome-wide chromatin profiling approaches have inherently limited resolution, complicating assessment of TF occupancy and co-occupancy, especially at individual alleles. In this work, we introduce Accessible Chromatin by Cytosine Editing Site Sequencing with ATAC-seq (ACCESS-ATAC), which harnesses a double-stranded DNA cytosine deaminase (Ddd) enzyme to stencil TF binding locations within accessible chromatin regions. We optimize bulk and single-cell ACCESS-ATAC protocols and develop computational methods to show that the increased resolution compared with ATAC-seq improves the accuracy of TF binding site prediction. We use ACCESS-ATAC to perform genome-wide allelic occupancy and co-occupancy imputation for 64 TFs each in HepG2 and K562, revealing that the propensity of a majority of TFs to co-occupy nearby motifs oscillates with a period approximating the helical turn of DNA. Altogether, ACCESS-ATAC expands the resolution and capabilities of bulk and single-cell epigenomic profiling.