Molecular Biology

Blunt End Protection

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Science  17 Aug 2012:
Vol. 337, Issue 6096, pp. 778
DOI: 10.1126/science.337.6096.778-d

One of the problems with having linear chromosomes, as most eukaryotes have, is their ends. Naked DNA ends are recognized by the cell as breaks in the continuity of the genome and are repaired with all haste. Trying to “repair” the ends of chromosomes, however, could have devastating consequences for the cell (the fusion of whole chromosomes, for example). Instead, special structures at chromosome ends, known as telomeres, whose general features have been conserved across evolution, protect them from the attentions of the cell's DNA repair machinery. Telomeres generally have a single-stranded (ss)DNA overhang that binds to proteins that help disguise the DNA end.

Surprisingly, Kazda et al. find that a substantial fraction of the telomeres in the plant Arabidopsis thaliana do not have canonical overhanging ssDNA ends. Rather, the chromosomes have blunt ends, which are probably a consequence of the replication of DNA. These blunt ends, which would be unable to bind the protective protein complex found on the other Arabidopsis telomeres, are bound by the Ku70/80 heterodimer, which is normally required for DNA repair but can also act to protect free DNA ends.

Genes Dev. 26, 1703 (2012).

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