MutSα deficiency increases tolerance to DNA damage in yeast lacking postreplication repair

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.