Sequence variation in the LEU2 region of the Saccharomyces cerevisiae genome

The LEU2 regions present on yeast plasmid vectors come from two sources, a series of strains derived from S288c and strain M 127. The LEU2 region from the S288c series contains a Tyl-17 element with its associated δ sequences and a small repetitive RNA gene while the LEU2 region from M 127 which is present on pJDB248, lacks the Tyl-17 element, but carries a δ sequence and a small RNA gene. The various LEU2 plasmids currently in use vary with respect to these sequences depending on which restriction fragment from the region is present on the recombinant molecule. In addition, strain M127 contains three LEU2 homologous sequences that are represented by different EcoRI fragments and which segregate independently at meiosis. Therefore, there are at least four forms of the centromere-distal EcoRI fragment of the LEU2 locus in the Saccharomyces cerevisiae gene pool; these are 7.1 kb, 1.9 kb, 1.48 kb and 1.15 kb long.