RNAPII and NER stall loop extrusion at UV lesions, shaping the 3D genome during repair

The three-dimensional (3D) genome architecture is highly elastic, adapting to nuclear processes such as transcription and the DNA damage response ^1,2 . Nucleotide excision repair (NER) acts within this chromatin context to detect and repair mutagenic lesions induced by ultraviolet (UV) irradiation ³ . UV irradiation has been shown to induce restructuring of the 3D genome across multiple scales, including chromatin compartments, domains, and loops. However, the extent to which NER activity contributes to this remodelling is unresolved, as the only prior study tracking such UV-induced changes was limited to repair-proficient cells ⁴ . Here, by combining genome-wide chromatin profiling of repair-deficient human cells with loop extrusion simulations, we show that lesion-stalled RNA polymerase II (RNAPII) and repair-associated barriers constrain loop extrusion. These events counter the loop-lengthening effects of UV-induced transcriptional shutdown, leading to shorter chromatin loops and reinforced chromatin domains that facilitate efficient lesion recognition and repair. The contribution by NER machinery underscores 3D genome reorganisation as an active mechanism both initiated and harnessed by DNA repair, rather than a passive consequence of DNA damage. The contribution by RNAPII extends its role beyond activating transcription-coupled repair to promoting a genome-wide repair-permissive state. Together, these findings advance our understanding of how nuclear processes coordinate on a shared chromatin substrate to preserve genome integrity.