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Updated: Aug 7, 2025
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Direct Restart of a Replication Fork Stalled by a Head-On RNA Polymerase
Published on: April 29, 2010
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Bacillus subtilis RadA/Sms-Mediated Nascent Lagging-Strand Unwinding at Stalled or Reversed Forks Is a Two-Step
Rubén Torres1, Begoña Carrasco1, Juan C Alonso1
1Department of Microbial Biotechnology, Centro Nacional de Biotecnología, CNB-CSIC, 28049 Madrid, Spain.
International Journal of Molecular Sciences
|March 11, 2023
Summary
Bacillus subtilis RecA and RadA/Sms proteins cooperate to unwind DNA replication forks. This coordinated action is essential for rescuing stalled forks and preventing unwanted DNA recombination.
Area of Science:
- Molecular Biology
- DNA Replication
- Protein-DNA Interactions
Background:
- Replication fork stability is crucial for genome integrity.
- Bacillus subtilis RecA, SsbA, RecO, and RadA/Sms proteins are involved in replication fork rescue.
- The precise roles and interplay of these proteins in fork remodeling remain incompletely understood.
Purpose of the Study:
- To elucidate the molecular mechanism by which RadA/Sms and RecA cooperate in replication fork remodeling.
- To understand how these proteins process reversed and stalled replication forks.
- To investigate the regulatory roles of RecA and RadA/Sms in fork processing and recombination.
Main Methods:
- Utilized reconstituted branched replication intermediates in vitro.
- Investigated the DNA binding and unwinding activities of RadA/Sms and RecA.
- Analyzed the effects of RecA mediators (RecO) and variants (RadA/Sms C13A) on fork processing.
Main Results:
- RadA/Sms unwinds the nascent lagging strand of reversed forks with longer lagging strands but requires RecA for unwinding gapped or leading-strand-dominant forks.
- A two-step mechanism was revealed: RadA/Sms displaces SsbA and nucleates RecA, followed by RecA recruiting RadA/Sms to unwind the nascent lagging strand.
- RecA limits RadA/Sms self-assembly, controlling fork processing, while RadA/Sms prevents excessive RecA-mediated recombination.
Conclusions:
- A novel two-step mechanism for replication fork unwinding involving RadA/Sms and RecA has been characterized.
- This coordinated action ensures efficient processing of stalled replication forks while preventing aberrant recombination.
- The findings provide critical insights into the intricate regulation of DNA replication and repair pathways.
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