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A role for topoisomerase III in a recombination pathway alternative to RuvABC
Christopher R Lopez1, Shirley Yang, Richard W Deibler
1Interdepartmental Program in Cell and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
Molecular Microbiology
|September 17, 2005
Summary
Topoisomerase III is essential for bacterial viability, playing a key role in DNA replication and recombination. Its absence, alongside topoisomerase IV, leads to synthetic lethality, highlighting its importance in maintaining genome stability.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- The physiological function of topoisomerase III remains largely unknown across organisms.
- Topoisomerase IV is crucial for resolving DNA topological problems during replication.
Purpose of the Study:
- To elucidate the physiological role of topoisomerase III in Escherichia coli.
- To investigate the interaction between topoisomerase III and topoisomerase IV in DNA replication and recombination.
Main Methods:
- Construction and analysis of double mutants lacking topoisomerase III and topoisomerase IV.
- Assessment of DNA replication intermediates, recombination proficiency, and sensitivity to DNA damaging agents.
- Genetic rescue experiments using null mutations in recombination-related genes (recQ, recA, helD, lexA).
Main Results:
- Simultaneous loss of topoisomerase III and topoisomerase IV (topoisomerase III/IV double mutant) results in inviability at permissive temperatures.
- Topoisomerase III is not essential for resolving DNA replication catenation when topoisomerase IV is absent.
- RecQ or RecA null mutations partially rescue the synthetic lethality of the topoisomerase III/IV double mutant, indicating a role in recombination.
- Topoisomerase III appears to function in disentangling recombination intermediates, potentially as an alternative pathway to the RuvABC complex.
- Topoisomerase III/RuvC double mutants exhibit increased sensitivity to UV and mitomycin C, and reduced transduction efficiency.
Conclusions:
- Topoisomerase III is essential for viability in Escherichia coli, particularly in conjunction with topoisomerase IV.
- Topoisomerase III plays a significant role in DNA recombination pathways, possibly by resolving complex recombination intermediates.
- The findings suggest a conserved mechanism for maintaining genome stability through the coordinated action of topoisomerases and recombination machinery.
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