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Published on: June 25, 2013
Saccharomyces cerevisiae checkpoint genes MEC1, RAD17 and RAD24 are required for normal meiotic recombination partner
J M Grushcow1, T M Holzen, K J Park
1Department of Radiation, University of Chicago, Chicago, Illinois 60637, USA.
Abstract:
Checkpoint gene function prevents meiotic progression when recombination is blocked by mutations in the recA homologue DMC1. Bypass of dmc1 arrest by mutation of the DNA damage checkpoint genes MEC1, RAD17, or RAD24 results in a dramatic loss of spore viability, suggesting that these genes play an important role in monitoring the progression of recombination. We show here that the role of mitotic checkpoint genes in meiosis is not limited to maintaining arrest in abnormal meioses; mec1-1, rad24, and rad17 single mutants have additional meiotic defects. All three mutants display Zip1 polycomplexes in two- to threefold more nuclei than observed in wild-type controls, suggesting that synapsis may be aberrant. Additionally, all three mutants exhibit elevated levels of ectopic recombination in a novel physical assay. rad17 mutants also alter the fraction of recombination events that are accompanied by an exchange of flanking markers. Crossovers are associated with up to 90% of recombination events for one pair of alleles in rad17, as compared with 65% in wild type. Meiotic progression is not required to allow ectopic recombination in rad17 mutants, as it still occurs at elevated levels in ndt80 mutants that arrest in prophase regardless of checkpoint signaling. These observations support the suggestion that MEC1, RAD17, and RAD24, in addition to their proposed monitoring function, act to promote normal meiotic recombination.
Insights
DNA damage checkpoint genes MEC1, RAD17, and RAD24 are crucial for monitoring meiotic recombination. Mutations in these genes lead to aberrant synapsis and increased ectopic recombination, impacting spore viability.
Area of Science:
- Cell Biology
- Genetics
- Molecular Biology
Background:
- Checkpoint genes, including MEC1, RAD17, and RAD24, regulate meiotic progression.
- Mutations in DMC1 block meiotic recombination and trigger checkpoint-mediated arrest.
- Bypassing this arrest with checkpoint gene mutations causes loss of spore viability.
Purpose of the Study:
- To investigate the role of DNA damage checkpoint genes (MEC1, RAD17, RAD24) in meiosis beyond monitoring.
- To determine if these genes influence meiotic recombination processes directly.
- To characterize meiotic defects in single mutants of mec1, rad17, and rad24.
Main Methods:
- Analysis of meiotic progression and spore viability in checkpoint gene mutants.
- Microscopic examination of synapsis using Zip1 polycomplexes.
- Physical assay to quantify ectopic recombination frequencies.
- Assessment of crossover association with recombination events.
Main Results:
- Mutants in MEC1, RAD17, and RAD24 exhibit increased Zip1 polycomplexes, indicating aberrant synapsis.
- Elevated levels of ectopic recombination were observed in all three mutants.
- rad17 mutants showed an altered frequency of crossover events.
- Ectopic recombination occurred even when meiotic progression was arrested (ndt80 mutants).
Conclusions:
- MEC1, RAD17, and RAD24 have roles in meiosis beyond checkpoint control.
- These genes actively promote normal meiotic recombination and synapsis.
- Checkpoint genes are essential for maintaining genome integrity during meiosis.
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