Mms4 chromosomal association reveals functional relationships between meiotic crossover pathways in budding yeast

Area of Science:

• * Genetics and Molecular Biology
• * Cell Biology
• * DNA Repair Mechanisms

Background:

• * Meiotic crossovers are essential for accurate chromosome segregation during gamete formation.
• * Crossovers arise from the repair of programmed DNA double-strand breaks (DSBs).
• * Two main pathways exist: Class I (Msh4-Msh5 dependent) and Class II (Mms4-Mus81 endonuclease).

Purpose of the Study:

• * To investigate the genome-wide localization of the Mms4 protein during meiosis in Saccharomyces cerevisiae.
• * To understand the relationship between Mms4 localization and DNA double-strand break sites.
• * To elucidate the role of Mms4 in the context of other meiotic recombination proteins like Msh5.

Main Methods:

• * Genome-wide chromatin immunoprecipitation followed by sequencing (ChIP-seq) to map Mms4 localization.
• * Analysis of Mms4 binding patterns relative to DSB hotspots.
• * Examination of Mms4 localization in various genetic backgrounds, including msh5 deletion mutants.

Main Results:

• * Mms4 exhibits a preference for weaker DSB sites, contrasting with Msh5's bias towards strong DSB sites.
• * Mms4 localization is independent of DSB formation but facilitated by chromosome axis assembly.
• * Mms4 binding is largely insensitive to heterozygosity, unlike Msh5.

Conclusions:

• * Mms4-Mus81 enhances meiotic recombination robustness by targeting weaker or divergent DSB hotspots.
• * Mms4 associates with chromosomal axes near recombination intermediates.
• * Findings challenge competitive models for Mms4 and Msh5 association on meiotic chromosomes.