Elimination of subtelomeric repeat sequences exerts little effect on telomere essential functions in <i>Saccharomyces cerevisiae</i>.

Abstract

Telomeres, which are chromosomal end structures, play a crucial role in maintaining genome stability and integrity in eukaryotes. In the baker's yeast <i>Saccharomyces cerevisiae</i>, 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 <i>S. cerevisiae</i> 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 <i>S. cerevisiae</i> 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.