Telomeres are the ends of our chromosomes. Made of many repeats of the same DNA sequence, they act like shoelace caps: they protect the gene-containing body of the chromosome from being worn down. Breakdowns in telomere maintenance are implicated in ageing and cancer.
Telomeric DNA sequences can form four-stranded structures. Online this week in Nature, Stephen Neidle and colleagues of the Institute of Cancer Research, London, describe the crystal structure of one such quadruplex grown at a potassium concentration like that inside a human cell. The folding and appearance of the DNA in this quadruplex is fundamentally different from previously published sodium-containing structures.
The new DNA structure suggests a straightforward path for telomere folding and unfolding. The quadruplexes are flat and propeller-shaped, and can form long stacks one on top of the other with their "blades" sticking out on all sides. This makes them easily recognizable by telomere-associated proteins.
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