Achievement of close, stable homolog juxtaposition in Saccharomyces cerevisiae meiosis

A unique aspect of meiosis is the segregation of homologous chromosomes at the meiosis I division. Prior to homolog disjunction, homologous chromosomes find each other within the nucleus and associate via pairing interactions. We have utilized a site-specific recombination system that probes the relative probabilities that pairs of chromosomal loci collide with one another in living cells to monitor chromosome colocalization in budding yeast meiosis. The Cre/ loxP assay monitors homologous and nonhomologous chromosome colocalization within a meiotic cell. Cre-mediated recombination levels between a pair of loxP sites located at an allelic position on homologous chromosomes was greater than between a pair of loxP sites located at ectopic positions on nonhomologous chromosomes during meiosis. We define this difference as a new, measurable state of homologous chromosome association referred to as "close, stable homolog juxtaposition" (CSHJ). Using the Cre/ loxP assay, this body of work set out to examine factors upregulated during meiosis or affecting processes presumed to affect close, stable homolog juxtaposition in Saccharomyces cerevisiae to better understand how CSHJ is achieved. Deletion mutant analysis has led to the conclusion that CSHJ during meiosis in budding yeast is dependent on meiotic recombination, occurs mostly independent of synapsis and is distinct from DSB-independent pairing contacts. Meiotic telomere reorganization contributes to CSHJ through recombination. Multiple branches of the meiotic recombination pathway contribute independently to homolog pairing and stable juxtaposition during meiosis in budding yeast. Taken together, the data generated during the course of this study has led to a greater understanding of how meiotic processes act in concert to bring about close, stable homolog juxtaposition in Saccharomyces cerevisiae meiosis.