Saccharomyces cerevisiae Mer3 is a DNA helicase involved in meiotic crossing over
Takuro Nakagawa1, Richard D Kolodner
1Ludwig Institute for Cancer Research, Cancer Center and Department of Medicine, University of California San Diego School of Medicine, La Jolla, California 92093-0660, USA.
Abstract:
Crossing over is regulated to occur at least once per each pair of homologous chromosomes during meiotic prophase to ensure proper segregation of chromosomes at the first meiotic division. In a mer3 deletion mutant of Saccharomyces cerevisiae, crossing over is decreased, and the distribution of the crossovers that occur is random. The predicted Mer3 protein contains seven motifs characteristic of the DExH box type of DNA/RNA helicases. The mer3G166D and the mer3K167A mutation, amino acid substitutions of conserved residues in a putative nucleotide-binding domain of the helicase motifs caused a defect in the transition of meiosis-specific double-strand breaks to later intermediates, decreased crossing over, and reduced crossover interference. The purified Mer3 protein was found to have DNA helicase activity. This helicase activity was reduced by the mer3GD mutation to <1% of the wild-type activity, even though binding of the mutant protein to single- and double-strand DNA was unaffected. The mer3KA mutation eliminated the ATPase activity of the wild-type protein. These results demonstrate that Mer3 is a DNA helicase that functions in meiotic crossing over.
Insights
Mer3 is a DNA helicase essential for proper meiotic crossing over in yeast. Mutations in Mer3 disrupt DNA repair and reduce crossover frequency, highlighting its role in ensuring accurate chromosome segregation.
Area of Science:
- Genetics
- Molecular Biology
- Biochemistry
Background:
- Meiotic recombination ensures accurate chromosome segregation.
- The Mer3 protein is implicated in regulating crossing over during meiosis.
Purpose of the Study:
- To investigate the function of the Mer3 protein in meiotic crossing over.
- To determine if Mer3 possesses DNA helicase activity and how mutations affect this activity.
Main Methods:
- Analysis of mer3 deletion and point mutants in Saccharomyces cerevisiae.
- Biochemical assays to assess Mer3 protein's DNA helicase and ATPase activities.
- Characterization of DNA repair intermediates in mer3 mutants.
Main Results:
- Mer3 deletion mutants exhibit reduced crossing over and random crossover distribution.
- Specific mutations (mer3G166D, mer3K167A) impair the transition of meiotic double-strand breaks and decrease crossing over.
- Purified Mer3 protein displays DNA helicase activity, which is abolished by the mer3KA mutation and significantly reduced by the mer3GD mutation.
Conclusions:
- Mer3 functions as a DNA helicase crucial for regulating meiotic crossing over.
- The helicase and ATPase activities of Mer3 are vital for its role in recombination and proper chromosome segregation.
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