Abstract
Interstrand crosslinks (ICLs) block transcription by mechanisms that remain incompletely understood. Cisplatin induces ICLs that suppress transcription and contribute to its antitumor activity but these effects can be mitigated by transcription-coupled repair. Using reconstituted transcription systems and cryo-electron microscopy, we investigated how RNA polymerase II (Pol II) processes cisplatin-ICLs and captured eight sequential transcriptional states. Pol II unexpectedly remodels the crosslinked guanines into a novel conformation positioned above the bridge helix. This rearranged ICL prevents the damaged base from entering the active site and triggers Pol II backtracking following ATP misincorporation. Furthermore, Cockayne syndrome protein B, an ATP-dependent translocase that initiates transcription-coupled repair, neither promotes lesion bypass nor displaces stalled Pol II, thereby committing the lesion to transcription-coupled repair. These findings identify Pol II as a structural remodeler of cisplatin-ICLs and reveal how the remodeled lesion stalls transcription, providing insight into cellular responses to platinum-based chemotherapy.