Identification and characterization of novel factors that influence minisatellite stability in stationary phase yeast cells

Abstract

The eukaryotic genome is primarily comprised of non-coding regions of DNA consisting of several different types of repetitive elements. Minisatellites are a type of tandem repetitive element and are composed of repeat units that are 15-100bp in length. Rare altered alleles of minisatellites are associated with an increased risk of several different types of disease including cancer, diabetes, epilepsy and coronary artery disease. However, little is known about what factors prevent minisatellites from alternating and becoming potential pathogenic alleles. Our lab previously developed a color segregation assay to detect minisatellite instability in the yeast saccharomyces cerevisiae. Using this assay, we discovered a unique color segregation phenotype known as `blebbing' which was shown to be indicative of minisatellite alterations that occurred in stationary phase yeast cells. Here, we perform a genome-wide screen known as the Synthetic Genetic Array (SGA) analysis to screen for mutants strains bearing different types of minisatellite alleles that produced a strong blebbing phenotype. Through our work, we identify over 100 candidate genes that regulate the stability of a minisatellite in stationary phase. Further characterization of specific subsets of these genes demonstrates that minisatellites are regulated by different factors depending upon the repeat unit composition and size. We also demonstrate the checkpoint and mismatch repair components are important for stationary phase minisatellite stability and that alterations occurring in mutant strains are mediated by mechanisms utilizing recombination. Together our work provides novel insight into the factors governing minisatellite stability in a unique population of non-dividing cells.