Nbs1 moving up in the world

The Nbs1 protein participates in the cell-cycle checkpoint response to DNA double-strand breaks (DSBs), but its precise mode of action — especially in relation to the checkpoint kinase Atm — has been debated. New mouse models suggest that Nbs1 is required for activation of Atm in response to DNA DSBs and that it also functions in an amplification loop with Atm that allows even a small number of DNA DSBs to mount a potent checkpoint response.