Investigating the role of G-quadruplexes at Saccharomyces cerevisiae telomeres.

The G-quadruplex consensus motif G_≥3N_xG_≥3N_xG_≥3N_xG_≥3 is found at telomeres of many species, ranging from yeast to plants to humans, but the biological significance of this fact remains largely unknown. In this study, we examine the in vivo relevance of telomeric G-quadruplexes in the budding yeast Saccharomyces cerevisiae by expressing a mutant telomerase RNA subunit (tlc1-tm) that introduces mutant [(TG)_0-4TGG]_xATTTGG telomeric repeats instead of wild-type (TG)_0-6TGGGTGTG(G)_0-1 repeats to the distal ends of telomeres. The tlc1-tm telomere sequences lack the GGG motif present in every wild-type repeat and, therefore, are expected to be impaired in the formation of G-quadruplexes. Circular dichroism analysis of oligonucleotides consisting of tlc1-tm telomeric sequence is consistent with this hypothesis. We have previously shown that tlc1-tm cells grow similarly to wild-type cells, suggesting that the ability to form telomeric G-quadruplexes is not essential for telomere capping in S. cerevisiae cells.