Multiple pathways regulate 3’ overhang generation at S. cerevisiae telomeres

Telomeres terminate with 3’ G-strand overhangs, which may play a role in regulating telomerase action. Generation of these overhangs is thought to occur by nucleolytic processing, but the mechanism is poorly understood. By using an inducible short telomere assay, we show that S. cerevisiae Sae2 and the Sgs1 RecQ helicase control two distinct but partially complementary pathways for telomere processing, and this Sae2 function requires its phosphorylation at serine 267. No processing activity is detectable in sae2Δ sgs1Δ double mutant cells, while the Exo1 exonuclease contributes to residual C-strand resection and telomere elongation in both sae2Δ and sgs1Δ cells. This finding suggests that either Sgs1 or Sae2 action is required for Exo1 to function at telomeres. In addition, also Dna2 might support Sgs1 activity, as it acts redundantly with Exo1, but not with Sgs1. Finally, both length maintenance and G-strand overhang generation at native telomeres are affected by concomitant lack of Sae2 and Sgs1. Thus, the combined activities of Sae2 and Sgs1 control telomere length by regulating telomere processing.