Evidence for a new step in telomere maintenance

The strand of telomeric DNA that runs 5'3' toward a chromosome end is typically G rich. Telomerase-generated G tails are expected at one end of individual DNA molecules. Saccharomyces telomeres acquire TG(1-3) tails late in S phase. Moreover, the telomeres of linear plasmids can interact when the TG(1-3) tails are present. Molecules that mimic the structures predicted for telomere replication intermediates were generated in vitro. These in vitro generated molecules formed telomere-telomere interactions similar to those on molecules isolated from yeast, but only if both ends that interacted had a TG(1-3) tail. Moreover, TG(1-3), tails were generated in vivo in cells lacking telomerase. These data suggest a new step in telomere maintenance, cell cycle-regulated degradation of the C(1-3)A strand, which can generate a potential substrate for telomerase and telomere-binding proteins at every telomere.