Multiple factors insulate Msh2-Msh6 mismatch repair activity from defects in Msh2 domain I

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• DNA mismatch repair (MMR) is crucial for genomic stability, correcting DNA polymerase errors.
• The Msh2-Msh6 and Msh2-Msh3 complexes play distinct roles in MMR, recognizing different types of DNA lesions.
• Mutations in Msh2, particularly in domain I, are linked to hereditary non-polyposis colorectal cancer (HNPCC).

Purpose of the Study:

• To investigate the functional consequences of the msh2Δ1 mutation, affecting Msh2's DNA-binding domain I, on MMR pathways.
• To understand how defects in Msh2 domain I contribute to increased mutation rates and HNPCC pathogenesis.
• To elucidate the interplay between Msh2 domain I, Msh6, and other cellular factors in MMR fidelity.

Main Methods:

• Genetic analysis of msh2Δ1 mutants combined with mutations in MSH6, pol3-01, and rad27.
• Phenotypic characterization of cellular mutational load in engineered yeast strains.
• In vitro DNA binding assays using purified Msh2-Msh6 complexes with the msh2Δ1 mutation.

Main Results:

• The msh2Δ1 mutation significantly impairs Msh2-Msh3-dependent MMR functions but has less impact on Msh2-Msh6-dependent repair.
• Combined mutations revealed msh2Δ1-specific phenotypes in Msh2-Msh6 repair, leading to elevated mutation rates.
• In vitro studies showed that msh2Δ1-Msh6 exhibits reduced specificity for DNA mismatches and altered DNA binding footprints.

Conclusions:

• Multiple cellular factors likely buffer the MMR system against defects in Msh2 domain I.
• The findings provide mechanistic insights into how Msh2 domain I mutations contribute to HNPCC development.
• This research highlights the critical, yet complex, role of Msh2's DNA-binding domain in maintaining genome integrity.