Optimized ChIP-exo for mammalian cells and patterned sequencing flow cells

By combining chromatin immunoprecipitation (ChIP) with an exonuclease that digests the ends of protein-bound DNA fragments, ChIP-exo characterizes genome-wide protein-DNA interactions at near base-pair resolution. However, the widespread adoption of ChIP-exo has been hindered by several technical challenges, including lengthy protocols, the need for multiple custom reactions, and incompatibilities with recent Illumina sequencing platforms. To address these barriers, we systematically optimized and adapted the ChIP-exo library construction protocol for the unique requirements of mammalian cells and current sequencing technologies. We introduce a Mammalian-Optimized ChIP-exo (MO-ChIP-exo) protocol that builds upon previous ChIP-exo protocols with systematic optimization of crosslinking, harvesting, and library construction. We validate MO-ChIP-exo by comparing it to previously published ChIP-exo protocols and demonstrate its adaptability to both suspension (K562) and adherent (HepG2, mESC) cell lines. This improved protocol provides a more robust and efficient method for generating high-quality ChIP-exo libraries from mammalian cells. Overall design: Optimization of the ChIP-exo protocol for mammalian cells and current DNA sequencing technologies, resulting in the MO-ChIP-exo protocol. Optimization was mainly performed using the CTCF antibody in K562 cells. Additional testing and validation was performed in HepG2 and mES cells and with the USF1 antibody.