When a dividing cell's DNA is damaged, that cell needs to stop dividing so that the damage can be repaired. There are two main points at which the cell-division cycle can be halted. A study of one of these -- the G2 DNA-damage checkpoint -- shows that there are two parts to checkpoint control. The first, checkpoint initiation, does not seem to depend on the tumour-suppressor protein p53. But maintenance of this checkpoint, it seems, does.
