mlh3 mutations in baker's yeast alter meiotic recombination outcomes by increasing noncrossover events genome-wide

Area of Science:

• Genetics
• Molecular Biology
• Biochemistry

Background:

• Mlh1-Mlh3 is an endonuclease involved in resolving double Holliday junctions during meiosis and plays a role in DNA mismatch repair (MMR).
• Understanding Mlh1-Mlh3 function in both processes is crucial for comprehending genome stability and meiotic recombination.
• Previous studies have suggested a role for Mlh1-Mlh3 in resolving meiotic crossovers and its involvement in MMR.

Purpose of the Study:

• To elucidate the structure-function relationship of Mlh3 in yeast.
• To investigate how Mlh1-Mlh3 interacts with other proteins, specifically MSH complexes, in MMR.
• To analyze the impact of Mlh3 mutations on meiotic recombination and MMR pathways.

Main Methods:

• Analysis of 60 new mlh3 alleles in baker's yeast (Saccharomyces cerevisiae).
• Purification and in vitro characterization of Mlh1-Mlh3 protein complexes.
• Construction of whole-genome recombination maps for various mlh3 mutants.

Main Results:

• Identified specific mlh3 alleles affecting either MMR or meiotic crossing over.
• Demonstrated that Mlh1-Mlh3 endonuclease activity is regulated by protein-protein interactions, particularly with MSH complexes.
• Observed an increase in noncrossover events in mlh3 mutants, indicating alternative resolution pathways for recombination intermediates.

Conclusions:

• Mlh3's enzymatic activity is modulated by protein interactions, crucial for its dual role in meiosis and MMR.
• Defects in meiotic components like Mlh3 can reroute meiotic recombination intermediates.
• Provides insights into the regulation of meiotic recombination pathways and the structure-function of Mlh3.