Related Experiment Videos
Highly mismatched molecules resembling recombination intermediates efficiently transform mismatch repair proficient
J Westmoreland1, G Porter, M Radman
1Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
Abstract:
The ability of related DNAs to undergo recombination decreases with increased sequence divergence. Mismatch repair has been proposed to be a key factor in preventing homeologous recombination; however, the contribution of mismatch repair is not universal. Although mismatch repair has been proposed to act by preventing strand exchange and/or inactivating multiply mismatched heteroduplexes, there has been no systematic study to determine at what step(s) in recombination mismatch repair acts in vivo. Since heteroduplex is a commonly proposed intermediate in many models of recombination, we have investigated the consequences of mismatch repair on plasmids that are multiply mismatched in heteroduplex structures that are similar to those that might arise during recombination. Plasmids containing multiply mismatched regions were transformed into wild-type and Mut+ Escherichia coli mutants. There was only a 30-40% reduction in transformation of Mut+ as compared to mutS and mutL strains for DNAs containing an 18% mismatched heteroduplex. The products obtained from mutS hosts differed from those obtained from Mut+ hosts in that there were many more colonies containing mixtures of two plasmids, due to survival of both strands of the heteroduplex. There were nearly 10 times more recombinants obtained from the mutS as compared to the wild-type host. Based on these results and those from other studies with E. coli and yeast, we propose that the prevention of recombination between highly diverged DNAs may be at a step earlier than heteroduplex formation.
Insights
Mismatch repair (MMR) hinders recombination between diverged DNAs. Our study suggests MMR acts before heteroduplex formation, impacting DNA repair and genetic diversity.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Recombination between related DNAs diminishes with increasing sequence divergence.
- Mismatch repair (MMR) is implicated in preventing homeologous recombination, but its precise role and timing in vivo remain unclear.
- Heteroduplex DNA is a proposed intermediate in recombination pathways.
Purpose of the Study:
- To investigate the in vivo role of mismatch repair in preventing recombination between highly diverged DNAs.
- To determine the specific step(s) in the recombination process where mismatch repair exerts its influence.
- To analyze the impact of mismatch repair on the survival and products of multiply mismatched heteroduplexes.
Main Methods:
- Transformation of multiply mismatched plasmids into wild-type and mismatch repair-deficient (mutS, mutL) Escherichia coli strains.
- Quantification of transformation efficiency and analysis of recombination products.
- Comparison of outcomes in MMR-proficient versus MMR-deficient hosts.
Main Results:
- A modest 30-40% reduction in transformation efficiency was observed in MMR-proficient (Mut+) strains compared to MMR-deficient (mutS, mutL) strains for 18% mismatched heteroduplexes.
- MMR-deficient hosts yielded significantly more colonies with mixed plasmids, indicating survival of both heteroduplex strands.
- Approximately a tenfold increase in recombinant products was observed in mutS hosts compared to wild-type hosts.
Conclusions:
- Mismatch repair plays a role in limiting recombination between highly diverged DNAs.
- The results suggest that mismatch repair may act at a stage preceding heteroduplex formation, rather than solely on existing heteroduplexes.
- These findings contribute to understanding the mechanisms that maintain genome stability and regulate homologous recombination.