In response to genotoxic stress, DNA damage checkpoints and repair pathways are activated that ensure DNA is transmitted intact. The kinase ataxia telangiectasia and Rad3-related protein (ATR), together with its downstream effector kinases, such as Chk1, is one of the master regulators of the DNA-damage-induced response (DDR). ATR is recruited to sites of DNA damage that are characterised by extended single-stranded (ss)DNA coated with replication protein A (RPA). Recruitment of additional proteins, such as Rad9-containing complexes, are required for activation of ATR and subsequent phosphorylation of downstream effector proteins. However, triggering a checkpoint arrest in the G2 phase of the cell cycle might involve a different mechanism, as the authors have previously shown that Rad9 does not localise to sites of UV-induced damage in G2 cells. To better understand the underlying checkpoint activation mechanism, Daniël Warmerdam, Veronique Smits and colleagues now (p. 1923) analyse the nuclear localisation of DDR factors after UV irradiation of G2 cells. They find that virtually no DDR proteins accumulate at DNA lesions but, interestingly, observe that p38 MAPK is phosphorylated and activated in these cells. However, to fully abrogate G2 arrest after UV damage, the authors needed to inhibit both p38 mitogen-activated protein kinase (MAPK) and the ATR–Chk1 pathway, suggesting that the two pathways have complementing roles in activating G2 arrest in response to UV light.