MutSα deficiency increases tolerance to DNA damage in yeast lacking postreplication repair
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Updated: Dec 20, 2025
Genetic Studies of Human DNA Repair Proteins Using Yeast as a Model System
Published on: March 18, 2010
Ingrid L Berg1, Jan-Olov Persson2, Stefan U Åström1
1Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, S-10691 Stockholm, Sweden.
Abstract:
By combining mutations in DNA repair genes, important and unexpected interactions between different repair pathways can be discovered. In this study, we identified a novel link between mismatch repair (MMR) genes and postreplication repair (PRR) in Saccharomyces cerevisiae. Strains lacking Rad5 (HLTF in mammals), a protein important for restarting stalled replication forks in the error-free PRR pathway, were supersensitive to the DNA methylating agent methyl methanesulfonate (MMS). Deletion of the mismatch repair genes, MSH2 or MSH6, which together constitutes the MutSα complex, partially suppressed the MMS super-sensitivity of the rad5Δ strain. Deletion of MSH2 also suppressed the MMS sensitivity of mms2Δ, which acts together with Rad5 in error-free PRR. However, inactivating the mismatch repair genes MSH3 and MLH1 did not suppress rad5Δ, showing that the suppression was specific for disabling MutSα. The partial suppression did not require translesion DNA synthesis (REV1, REV3 or RAD30), base excision repair (MAG1) or homologous recombination (RAD51). Instead, the underlying mechanism was dependent on RAD52 while independent of established pathways involving RAD52, like single-strand annealing and break-induced replication. We propose a Rad5- and Rad51-independent template switch pathway, capable of compensating for the loss of the error-free template-switch subpathway of postreplication repair, triggered by the loss of MutSα.
Insights
Unexpected interactions between DNA repair pathways were discovered. Loss of mismatch repair genes partially suppressed sensitivity to DNA damage in yeast lacking the Rad5 protein, revealing a novel link.
Area of Science:
- Molecular Biology
- Genetics
- DNA Repair Mechanisms
Background:
- DNA repair pathways are crucial for maintaining genomic stability.
- Interactions between different DNA repair pathways are complex and not fully understood.
- Postreplication repair (PRR) handles replication fork stalling and DNA damage bypass.
Purpose of the Study:
- To investigate novel interactions between mismatch repair (MMR) and postreplication repair (PRR) pathways.
- To identify the specific MMR genes involved in suppressing sensitivity in PRR-deficient mutants.
- To elucidate the mechanism underlying the observed suppression.
Main Methods:
- Utilized Saccharomyces cerevisiae (yeast) as a model organism.
- Generated strains with combined mutations in MMR (MSH2, MSH6, MSH3, MLH1) and PRR (RAD5, MMS2) genes.
- Assessed sensitivity to methyl methanesulfonate (MMS), a DNA methylating agent.
- Investigated the requirement of other DNA repair pathways (translesion synthesis, base excision repair, homologous recombination) and RAD52-dependent pathways.
Main Results:
- Strains lacking Rad5 showed extreme sensitivity to MMS.
- Deletion of MSH2 or MSH6 partially suppressed the MMS sensitivity of rad5Δ strains.
- This suppression was specific to the MutSα complex (Msh2/Msh6) and not observed with Msh3 or Mlh1.
- The suppression mechanism was independent of translesion synthesis, base excision repair, and homologous recombination.
- The underlying pathway was dependent on RAD52 but not on established RAD52-mediated pathways.
Conclusions:
- A novel link exists between mismatch repair (MMR) and postreplication repair (PRR) in yeast.
- Loss of MutSα function can compensate for the absence of Rad5 in error-free PRR.
- A Rad5- and Rad51-independent template switch pathway is proposed to explain the suppression.
- This pathway is triggered by the loss of MutSα and compensates for the error-free template-switch subpathway of PRR.
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