This study investigates the chromatin context-dependent regulation and epigenetic manipulation of prime editing, a precise genome engineering tool. The authors developed a highly sensitive method to map the genomic locations of randomly integrated reporters, revealing strong position effects on prime editing efficiency. These effects are well predicted by chromatin marks, such as H3K79me2 and H3K9me3. The study also developed a multiplex perturbational framework to assess the interaction of trans-acting factors with the cis-chromatin environment on editing outcomes. Using this framework, they identified HLTF as a context-dependent repressor of prime editing. Additionally, they found that active transcriptional elongation enhances prime editing efficiency, and this can be modulated by CRISPR-mediated silencing or activation. The study demonstrates that epigenetic conditioning of a locus can significantly influence prime editing efficiency, providing a new strategy to enhance prime editing outcomes.This study investigates the chromatin context-dependent regulation and epigenetic manipulation of prime editing, a precise genome engineering tool. The authors developed a highly sensitive method to map the genomic locations of randomly integrated reporters, revealing strong position effects on prime editing efficiency. These effects are well predicted by chromatin marks, such as H3K79me2 and H3K9me3. The study also developed a multiplex perturbational framework to assess the interaction of trans-acting factors with the cis-chromatin environment on editing outcomes. Using this framework, they identified HLTF as a context-dependent repressor of prime editing. Additionally, they found that active transcriptional elongation enhances prime editing efficiency, and this can be modulated by CRISPR-mediated silencing or activation. The study demonstrates that epigenetic conditioning of a locus can significantly influence prime editing efficiency, providing a new strategy to enhance prime editing outcomes.