Comparison of Two Budding Yeast Disome Model Systems: Similarities, Difference, and Conflict

Here we define chromosome instability as the propensity of error-prone DNA repair and maintenance to generate chromosomal alterations known as gross chromosomal rearrangements (GCR), which can be found in a variety of forms in a variety of diseased cells. Insights and study of GCRs and chromosome instability can be gained through experimentation using a disome system (a haploid strain with an extra copy of one chromosome). Chromosome instability has previously been investigated and identified in a budding yeast ChrVII disome model. Here we extend and compare the study of chromosome instability using a similar ChrV disome system. As with the ChrVII disome system, cells containing unstable chromosomes form a distinctive “sectored” colony phenotype and through the use of genetic markers, we also find evidence of allelic recombination and chromosome loss. We also found the same DNA integrity pathways suppress chromosome instability and that unstable chromosomes are not generated through homologous recombination (HR) or non-homologous end-joining (NHEJ), similar to the ChrVII system. But in contrast and more interestingly, we did not detect any altered ChrV sizes, which conflicts with a previous ChrVII disome study where it was thought that unstable chromosomes often resulted in altered sizes. We also discovered a distinct increase in frequency of instability in the ChrV system compared to the ChrVII system.