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Genotoxins trigger nascent strand degradation (NSD) and replication fork reversal by causing uncoupling. The replicative helicase remains bound during these genome stability events.

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Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Genotoxins induce nascent strand degradation (NSD) and replication fork reversal, processes vital for genome stability.
  • These mechanisms are targeted by chemotherapy, but their triggers and the behavior of the replicative helicase remain unclear.

Purpose of the Study:

  • To investigate the triggers and mechanisms of NSD and replication fork reversal.
  • To determine the fate of the replicative helicase during these DNA replication stress responses.

Main Methods:

  • Developed a biochemical approach using Xenopus egg extracts for synchronous, localized NSD and fork reversal studies.
  • Validated findings with experiments in human cells.

Main Results:

  • Replication fork uncoupling was shown to stimulate NSD of nascent strands and promote fork reversal.
  • The replicative helicase was observed to remain bound throughout NSD and fork reversal.
  • NSD was found to occur both before and after fork reversal, suggesting multiple degradation steps.

Conclusions:

  • Replication fork uncoupling is a key trigger for both NSD and fork reversal.
  • Elucidated critical events preceding fork reversal, including multiple NSD steps.
  • Demonstrated the persistent binding of the replicative helicase during these DNA damage responses.