In general, there are multiple pathways taken by cells to repair the same DNA damage, and the choice of repair pathway is important for maintaining genomic fidelity. Cross-linking between DNA strands covalently links two DNA strands together, thereby blocking DNA replication and transcription, chemotherapy takes effect by utilizing the cytotoxicity of these crosslinks. In Xenopus laevis egg extracts, the collision of the replication fork with the interstrand crosslinker initiated two…