Elimination of subtelomeric repeat sequences exerts little effect on telomere essential functions in Saccharomyces...

Telomeres, which are chromosomal end structures, play a crucial role in maintaining genome stability and integrity in eukaryotes. In the baker's yeast Saccharomyces cerevisiae, the X- and Y'-elements are subtelomeric repetitive sequences found in all 32 and 17 telomeres, respectively. While the Y'-elements serve as a backup for telomere functions in cells lacking telomerase, the function of the X-elements remains unclear. This study utilized the S. cerevisiae strain SY12, which has three chromosomes and six telomeres, to investigate the role of X-elements (as well as Y'-elements) in telomere maintenance. Deletion of Y'-elements (SY12^YΔ), X-elements (SY12^XYΔ+Y), or both X- and Y'-elements (SY12^XYΔ) did not impact the length of the terminal TG_1-3 tracks or telomere silencing. However, inactivation of telomerase in SY12^YΔ, SY12^XYΔ+Y, and SY12^XYΔ cells resulted in cellular senescence and the generation of survivors. These survivors either maintained their telomeres through homologous recombination-dependent TG_1-3 track elongation or underwent microhomology-mediated intra-chromosomal end-to-end joining. Our findings indicate the non-essential role of subtelomeric X- and Y'-elements in telomere regulation in both telomerase-proficient and telomerase-null cells and suggest that these elements may represent remnants of S. cerevisiae genome evolution. Furthermore, strains with fewer or no subtelomeric elements exhibit more concise telomere structures and offer potential models for future studies in telomere biology.