Telomeres, specialized protein–DNA complexes that cap the ends of linear chromosomes, are essential for protecting chromosomes from degradation and end-to-end fusions1,2. The Pot1 (protection of telomeres 1) protein is a widely distributed eukaryotic end-capping protein, having been identified in fission yeast, microsporidia, plants and animals3,4. Schizosaccharomyces pombe Pot1p is essential for telomere maintenance3, and human POT1 has been implicated in telomerase regulation5,6. Pot1 binds telomeric single-stranded DNA (ssDNA) with exceptionally high sequence specificity7, the molecular basis of which has been unknown. Here we describe the 1.9-Å-resolution crystal structure of the amino-terminal DNA-binding domain of S. pombe Pot1p complexed with ssDNA. The protein adopts an oligonucleotide/oligosaccharide-binding (OB) fold8 with two loops that protrude to form a clamp for ssDNA binding. The structure explains the sequence specificity of binding: in the context of the Pot1 protein, DNA self-recognition involving base-stacking and unusual G–T base pairs compacts the DNA. Any sequence change disrupts the ability of the DNA to form this structure, preventing it from contacting the array of protein hydrogen-bonding groups. The structure also explains how Pot1p avoids binding the vast excess of RNA in the nucleus.
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We thank F. Guo, L. Chen and D. Theobald for insightful discussions, and G. Meigs and K. Henderson from ALS beamlines 8.2.1 and 8.2.2 for help in data collection. P.B. thanks W. Nudson and J. Bunch for technical assistance. This work was supported by the National Institutes of Health (T.R.C.) and by the Stowers Institute for Medical Research (P.B.). M.L. is a research fellow of the Helen Hay Whitney Foundation.
The authors declare that they have no competing financial interests.
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Lei, M., Podell, E., Baumann, P. et al. DNA self-recognition in the structure of Pot1 bound to telomeric single-stranded DNA. Nature 426, 198–203 (2003). https://doi.org/10.1038/nature02092
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