Telomere capping conceals chromosome ends from exonucleases and checkpoints, but the full range of capping mechanisms is not well defined. Telomeres have the potential to form G-quadruplex (G4) DNA, although evidence for telomere G4 DNA function in vivo is limited. In budding yeast, capping requires the Cdc13 protein and is lost at nonpermissive temperatures in cdc13-1 mutants. Here, we use several independent G4 DNA–stabilizing treatments to suppress cdc13-1 capping defects. These include overexpression of three different G4 DNA binding proteins, loss of the G4 DNA unwinding helicase Sgs1, or treatment with small molecule G4 DNA ligands. In vitro, we show that protein-bound G4 DNA at a 3′ overhang inhibits 5′→3′ resection of a paired strand by exonuclease I. These findings demonstrate that, at least in the absence of full natural capping, G4 DNA can play a positive role at telomeres in vivo.
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We thank the members of the Johnson and Yatsunyk labs for helpful discussions and comments on the manuscript; N. Maizels, M. Fry, K. Runge, V. Zakian, J.-L. Mergny, S. Berger, R. Marmorstein and P. Adams for discussions; S. Murakami (Kanazawa University), E. Blackburn (University of California, San Francisco), M. Charbonneau (École Normale Supérieure), S. Brill (Rutgers University), S. Gasser (Friedrich Miescher Institute) and M. Van Dyke (MD Anderson Cancer Center) for providing strains and plasmids, and D. Durocher (University of Toronto) for the Rad53 antibody. This work was supported by US National Institutes of Health grants R01 AG021521 (F.B.J.), P01 AG031862 (F.B.J.), T32 GM008216-22 (J.S.S.) and T32 GM07229 (J.S.S.), a Camille and Henry Dreyfus Faculty Startup Award (L.A.Y.), Research Corporation Award no. 7843 (L.A.Y.), a Deutscher Akademischer Austausch Dienst Fellowship (R.K.) and by a Cancer Research UK program grant (S.B.).
The authors declare no competing financial interests.
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Smith, J., Chen, Q., Yatsunyk, L. et al. Rudimentary G-quadruplex–based telomere capping in Saccharomyces cerevisiae. Nat Struct Mol Biol 18, 478–485 (2011). https://doi.org/10.1038/nsmb.2033
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