Cdc13 prevents telomere uncapping and Rad50-dependent homologous recombination

Cdc13 performs an essential function in telomere end protection in budding yeast. Here, we analyze the consequences on telomere dynamics of cdc13 ‐induced telomeric DNA damage in proliferating cells. Checkpoint‐deficient cdc13‐1 cells accumulated DNA damage and eventually senesced. However, these telomerase‐proficient cells could survive by using homologous recombination but, contrary to telomerase‐deficient cells, did so without prior telomere shortening. Strikingly, homologous recombination in cdc13‐1 mec3 , as well as in telomerase‐deficient cdc13‐1 cells, which were Rad52‐ and Rad50‐dependent but Rad51‐independent, exclusively amplified the TG 1–3 repeats. This argues that not only short telomeres are substrates for type II recombination. The Cdc13‐1 mutant protein harbored a defect in its association with Stn1 and Ten1 but also an additional, unknown, defect that could not be cured by expressing a Cdc13‐1–Ten1–Stn1 fusion. We propose that Cdc13 prevents telomere uncapping and inhibits recombination between telomeric sequences through a pathway distinct from and complementary to that used by telomerase.