Molecular Cell
Volume 37, Issue 4, 26 February 2010, Pages 492-502
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Article
Hydroxyurea-Stalled Replication Forks Become Progressively Inactivated and Require Two Different RAD51-Mediated Pathways for Restart and Repair

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Summary

Faithful DNA replication is essential to all life. Hydroxyurea (HU) depletes the cells of dNTPs, which initially results in stalled replication forks that, after prolonged treatment, collapse into DSBs. Here, we report that stalled replication forks are efficiently restarted in a RAD51-dependent process that does not trigger homologous recombination (HR). The XRCC3 protein, which is required for RAD51 foci formation, is also required for replication restart of HU-stalled forks, suggesting that RAD51-mediated strand invasion supports fork restart. In contrast, replication forks collapsed by prolonged replication blocks do not restart, and global replication is rescued by new origin firing. We find that RAD51-dependent HR is triggered for repair of collapsed replication forks, without apparent restart. In conclusion, our data suggest that restart of stalled replication forks and HR repair of collapsed replication forks require two distinct RAD51-mediated pathways.

Highlights

► RAD51 promotes replication fork restart after short hydroxyurea (HU) blocks ► RAD51-mediated fork restart does not create homologous recombination (HR) products ► Long HU blocks lead to fork collapse; replication is restarted by new origin firing ► Collapsed replication forks are repaired by classical RAD51-dependent HR

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Present address: Departments of Radiation Oncology and Environmental Health Sciences, University of Michigan, Ann Arbor, MI 48109-5637, USA