Isolation of Yeast Genes that Suppress the Chromosome Loss Defect of ysm's 22, 77, 83, and 84

Abstract

Cancer cells display both chromosome rearrangements and abnormal numbers of chromosomes. High fidelity chromosome transmission requires the accuracy of multiple processes such as DNA replication, DNA repair, sister chromatid cohesion, mitotic spindle assembly, and chromosome segregation. Many of the gene products that function in these processes are conserved in eukaryotes. The simple eukaryote Saccharomyces cerevisiae (budding yeast) is an excellent model system for the study of chromosome transmission as its cell cycle is well-characterized, and it is amenable to genetic analysis. With the aim of identifying genes important for chromosome transmission, we previously generated a collection of YAC stability in mitosis (ysm) mutants that display increased loss of a yeast artificial chromosome (YAC). Four mutant strains (ysm's 22, 77, 83, 84) are particularly interesting as they display high levels of YAC loss and have at least one additional mutant phenotype related to a process important for genome stability (e.g., DNA replication, mitotic spindle assembly). Isolation of suppressors of the YAC loss phenotype in these mutants may reveal the defective genes in these strains as well as genes whose products interact in the same or parallel pathways as the defective gene product. To this end, ysm's 22, 77, 83, and 84 were transformed with a yeast genomic plasmid library, and plasmids that suppressed the YAC loss phenotype were isolated. We are in the process of verifying candidate suppressor plasmids by retransformation of the mutant strains and identifying the suppressing genes by DNA sequencing. Analysis of these suppressors will contribute to our understanding of gene products, protein networks, and processes important for eukaryotic genome stability.