Updated project metadata. DNA interstrand crosslinks (ICLs) block replication fork progression by inhibiting DNA strand separation. Repair of ICLs requires sequential incisions, translesion DNA synthesis, and homologous recombination, but the full set of factors involved in these transactions remains unknown. Here we established CHROmatin MASS spectrometry (CHROMASS) to study protein recruitment dynamics during perturbed DNA replication in Xenopus egg extracts. Using CHROMASS, we systematically monitored protein assembly and disassembly at ICL-containing chromatin. Among numerous prospective new DNA repair factors we identified SLF1 and SLF2, which form a complex with RAD18 and together define a new pathway that suppresses genome instability by recruiting the SMC5/6 cohesion complex to DNA lesions. Our study provides the first global analysis of an entire DNA repair pathway and reveals the mechanism of SMC5/6 relocalization to damaged DNA in vertebrate cells.