Molecular biology: Damage control

The chemical composition of normal DNA at the end of chromosomes does not differ from that of damaged and broken DNA within chromosomes. New findings hint at how the DNA-repair machinery distinguishes the two.

The maintenance of genome integrity is crucial for the survival of every organism. So even a single break along a chromosome triggers a molecular signalling cascade that leads to an appropriate DNA-damage response (DDR). This response allows recognition of the damage site and decelerates cell-cycle progression, giving the cell a chance to repair the damage¹. Theoretically, the two free ends of each eukaryotic linear chromosome — telomeres — should evoke a similar cellular response. However, as long as they are intact, telomeres activate DDR only transiently, if at all, at defined stages of the cell cycle. In a paper published on page 1068 of this issue, Lazzerini Denchi and de Lange² provide clues on how this is achieved at a molecular level.