Abstract
Distinct protein assemblies are nucleated at telomeric DNA to both guard the ends from damage and lengthen the DNA after replication. In yeast, Cdc13 recruits either Stn1-Ten1 to form a protective cap or the telomerase holoenzyme to extend the DNA. We have established an in vitro yeast telomere system in which Stn1-Ten1–unextendable or telomerase-extendable states can be observed. Both assemblies are Cdc13 dependent, as the Cdc13 C-terminal region supports Stn1-Ten1 interactions and the N-terminal region contains a telomerase-activation function. Notably, the yeast Hsp90 chaperone Hsp82 mediates the switch between the telomere capping and extending structures by modulating the DNA binding activity of Cdc13. Taken together, our data show that the Hsp82 chaperone facilitates telomere DNA maintenance by promoting transitions between two operative complexes and by reducing the potential for binding events that would otherwise block the assembly of downstream structures.
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Acknowledgements
We dedicate the present work to our enduring memories of Oyetunji A. Toogun. We thank J. Barral (University of Texas Medical Branch) for the CH184 Escherichia coli strain; V. Lundblad (Salk Institute) for the Cdc13 constructs; V. Zakian (Princeton University) for the CDC13-Myc9x and EST2-Myc9x yeast strains; D. Shore (University of Geneva) for Stn1 and Ten1 vectors; and A. Belmont, W. Brieher, P. Newmark and D. Rivier for helpful comments on the manuscript. D.C.D. was supported by a Cellular, Biochemical and Molecular Sciences training grant from the National Institutes of Health, and B.C.F. was supported by US Public Health Service grant DK074270.
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D.C.D. designed and conducted experiments, O.A.T. designed and conducted experiments, F.J.E. conducted experiments, and B.C.F. designed and conducted experiments and wrote the manuscript.
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DeZwaan, D., Toogun, O., Echtenkamp, F. et al. The Hsp82 molecular chaperone promotes a switch between unextendable and extendable telomere states. Nat Struct Mol Biol 16, 711–716 (2009). https://doi.org/10.1038/nsmb.1616
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DOI: https://doi.org/10.1038/nsmb.1616