Cells often utilize multiple pathways to repair the same DNA lesion, and pathway choice has profound implications for the fidelity of genome maintenance. DNA interstrand cross-links (ICLs) block DNA replication and transcription by covalently linking the two strands of DNA, and the cytotoxicity of ICLs is exploited for chemotherapy. In Xenopus egg extracts, replication fork collision with ICLs initiates two distinct repair pathways. The NEIL3 glycosylase can cleave the cross-link 1 , but if this fails, the Fanconi anemia (FA) proteins incise the phosphodiester backbone surrounding the ICL, generating a double-strand break (DSB) intermediate that is repaired by homologous recombination 2 . How the simpler NEIL3 pathway is prioritized over the FA pathway, which can cause genomic rearrangements, is unknown. Here, we show that the E3 ubiquitin ligase Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Translesion synthesis DNA polymerases contribute to DNA damage tolerance by mediating replication of damaged templates. Due to the low fidelity of these enzymes, lesion bypass is often mutagenic. We have previously shown that, in Saccharomyces cerevisiae, the contribution of the error-prone DNA polymerase z (Polz) to replication and mutagenesis is greatly enhanced if the normal replisome is defective due to mutations in replication genes. Here we present evidence that this defective-replisome-induced mutagenesis (DRIM) results from the participation of Polz in the copying of undamaged DNA rather than from mutagenic lesion bypass. First, DRIM is not elevated in strains that have a high level of endogenous DNA lesions due to defects in nucleotide excision repair or base excision repair pathways. Second, DRIM remains unchanged when the level of endogenous oxidative DNA damage is decreased by using anaerobic growth conditions. Third, analysis of the spectrum of mutations occurring during DRIM reveals the characteristic error signature seen during replication of undamaged DNA by Polz in vitro. These results extend earlier findings in Escherichia coli indicating that Y-family DNA polymerases can contribute to the copying of undamaged DNA. We also show that exposure of wild-type yeast cells to the replication inhibitor hydroxyurea causes a Polz-dependent increase in mutagenesis. This suggests that DRIM represents a response to replication impediment per se rather than to specific defects in the replisome components.

Highlights d Replication fork collapse is triggered by mitotic CDKdependent CMG unloading d Mitotic CMG unloading requires the E3 ubiquitin ligase TRAIP and the p97 ATPase d Mitotic processing of stalled forks enables high-fidelity chromosome segregation d New model for the generation of complex chromosome rearrangements