Dual DNA-binding capability of Cdc13 coordinates with Ku to safeguard telomere integrity

In eukaryotes, telomeres, nucleoprotein complexes assembled on telomeric 3-overhang DNA, protect linear chromosome ends from degradation and inappropriate DNA repair. In budding yeast, Saccharomyces cerevisiae, telomere assembly involves the Cdc13-Stn1-Ten1 (CST) complex, the Ku70-Ku80 (Ku) complex, and the Rap1-Rif1-Rif2 complex. Among these, the CST complex, centered on the binding of the G-rich single-stranded region by the Cdc13 subunit, is essential for telomere maintenance and protection. Here, we show that Cdc13 also interacts with the duplex DNA adjoining its bound single strand. This junction binding enables Cdc13 to reposition the Ku complex, potentially suppressing Ku-mediated end joining, while allowing the Cdc13 and Ku complexes to synergize in protecting telomeric DNA ends, a function that can be disrupted by mutation of a conserved residue (K504E). cdc13-K504E cells remain viable but are hypersensitive to Exo1 overexpression, particularly when combined with ku80{Delta}. Surprisingly, cdc13-K504E and other telomere protection mutants are prone to adaptive metabolic reprogramming during stationary-phase growth, leading to increased fitness. This reprogramming is inheritable and centers on elevated expression of thiamine biosynthesis, salvage, and intake pathways. Our findings reveal a stress-induced adaptive response associated with telomere erosion, indicating that telomere erosion may serve as a timer for its activation.