(A) Mutations in Cdc13EBM-C (cdc13E252K, cdc13F253A and cdc13S255A) exhibited critically short telomeres. Cells were taken from serial streaks 2, 4 and 6 after sporulation. Vertical white spaces between lanes 1 and 2, 7 and 8, indicate cropping of superfluous lanes. (B) Strains as described in (A) were streaked onto plates to analyze senescence phenotype. (C) Fusion of Cdc13-Est2 cannot fully bypass the role of Est1. A diploid CDC13/cdc13Δ EST1/est1Δ strain was cotransformed with plasmids expressing Cdc13-Est2 (or Cdc13–2-Est2) and Est1 (or Est1–60). After sporulation, cells were taken from streak 6 and subjected to southern blot analysis. (D) A schematic model for telomerase recruitment to telomeres in budding yeast.