Related Experiment Video
Updated: May 4, 2026
Visualization of DNA Repair Proteins Interaction by Immunofluorescence
Published on: June 26, 2020
Mlh1-Mlh3, a meiotic crossover and DNA mismatch repair factor, is a Msh2-Msh3-stimulated endonuclease
Maria V Rogacheva1, Carol M Manhart, Cheng Chen
1From the Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703.
Abstract:
Crossing over between homologous chromosomes is initiated in meiotic prophase in most sexually reproducing organisms by the appearance of programmed double strand breaks throughout the genome. In Saccharomyces cerevisiae the double-strand breaks are resected to form three prime single-strand tails that primarily invade complementary sequences in unbroken homologs. These invasion intermediates are converted into double Holliday junctions and then resolved into crossovers that facilitate homolog segregation during Meiosis I. Work in yeast suggests that Msh4-Msh5 stabilizes invasion intermediates and double Holliday junctions, which are resolved into crossovers in steps requiring Sgs1 helicase, Exo1, and a putative endonuclease activity encoded by the DNA mismatch repair factor Mlh1-Mlh3. We purified Mlh1-Mlh3 and showed that it is a metal-dependent and Msh2-Msh3-stimulated endonuclease that makes single-strand breaks in supercoiled DNA. These observations support a direct role for an Mlh1-Mlh3 endonuclease activity in resolving recombination intermediates and in DNA mismatch repair.
Insights
The Mlh1-Mlh3 endonuclease resolves recombination intermediates during meiosis, facilitating chromosome segregation. This DNA mismatch repair factor directly impacts crossover formation and DNA repair pathways.
Area of Science:
- Genetics
- Molecular Biology
- Cell Biology
Background:
- Homologous recombination initiates meiosis via programmed double-strand breaks.
- In yeast, these breaks are processed into Holliday junctions, resolved into crossovers for proper chromosome segregation.
- Msh4-Msh5 stabilizes intermediates, while Sgs1 helicase, Exo1, and Mlh1-Mlh3 are implicated in resolution.
Purpose of the Study:
- To investigate the endonuclease activity of Mlh1-Mlh3 in resolving recombination intermediates.
- To elucidate the direct role of Mlh1-Mlh3 in crossover formation and DNA mismatch repair.
Main Methods:
- Purification of the Mlh1-Mlh3 complex.
- Biochemical assays to assess endonuclease activity on supercoiled DNA.
- Investigating Msh2-Msh3 stimulation and metal ion dependence.
Main Results:
- Mlh1-Mlh3 was purified and characterized as a metal-dependent endonuclease.
- The enzyme shows Msh2-Msh3-stimulated activity, introducing single-strand breaks in supercoiled DNA.
- These findings support a direct role for Mlh1-Mlh3 in resolving recombination intermediates.
Conclusions:
- Mlh1-Mlh3 possesses endonuclease activity crucial for resolving meiotic recombination intermediates.
- This activity directly contributes to crossover formation and homolog segregation during meiosis.
- The study provides evidence for Mlh1-Mlh3's dual role in recombination and DNA mismatch repair.
Related Concept Videos
01:36Mismatch Repair
01:20Mismatch Repair
The Mutator Protein Family Plays a Key Role in DNA Mismatch Repair
The human genome has more than 3 billion base pairs of DNA per cell. Prior to cell division, that vast amount of genetic...
01:36Mismatch Repair
02:31Homologous Recombination
02:31Homologous Recombination
02:04Fixing Double-strand Breaks