A yeast strain producing lys2 deletions at a high frequency after sporulation

A diploid yeast strain with extensive sequence dissimilarity in homologous regions near the LYS2 locus was sporulated, and spontaneous lys2 and lys5 mutant spores, selected on α-amino adipate, were analyzed. As many as 50% of the mutant spores contained a deletion in LYS2. These deletions occurred at a frequency of 5.0 × 10−7. While deletions of various sizes and endpoints were obtained, all the deletions recovered in this study included the border between homologous and non-homologous sequences located 4 kb upstream of LYS2. Large lys2 deletions that extended into an adjacent CYH2 duplication occurred at a frequency of 2.0 × 10−7, more than 1,000 times the frequency of the CYH2-LYS2 deletions found in a related haploid strain. This high frequency of CYH2-LYS2 deletions was observed only after sporulation of the diploid strain, and was dependent upon extensive sequence dissimilarity near the LYS2 locus.