A mutation in the MSH6 subunit of the Saccharomyces cerevisiae MSH2-MSH6 complex disrupts mismatch recognition

Area of Science:

• Molecular biology
• Genetics
• Biochemistry

Background:

• MSH2 forms complexes with MSH6 and MSH3 to repair DNA mismatches.
• MSH2-MSH6 repairs base pair and single nucleotide mismatches.
• MSH2-MSH3 repairs small insertion/deletion loop mismatches.

Purpose of the Study:

• To investigate the functional impact of a specific msh6 mutation, msh6-F337A, on DNA mismatch repair pathways in yeast.
• To determine the mechanism by which msh6-F337A affects the interactions within the MSH2-MSH6 and MSH2-MSH3 complexes.

Main Methods:

• Genetic analysis of yeast strains.
• Overexpression of the msh6-F337A mutation in wild-type yeast.
• Biochemical assays including UV cross-linking, filter binding, and gel retardation.
• ATPase and dissociation rate analysis.

Main Results:

• The msh6-F337A mutation conferred defects in both MSH2-MSH6 and MSH2-MSH3 dependent mismatch repair.
• Genetic analysis indicated msh6-F337A sequesters MSH2, disrupting its interactions with MSH3 and MSH6.
• The MSH2-msh6-F337A complex showed impaired mismatch recognition and formed an unproductive complex unable to stably bind DNA.

Conclusions:

• The msh6-F337A mutation disrupts DNA mismatch repair by forming an unproductive MSH2 complex.
• This mutation highlights the critical role of MSH2 interactions in maintaining functional DNA repair pathways.
• Understanding these molecular mechanisms is crucial for insights into genome stability.