CHK2 functions downstream of ATM (ataxia telangiectasia-mutated protein) in response to DNA damage to phosphorylate p53 and BRCA1 and thereby regulate the tumour suppressor functions of these proteins (Chehab et al, 2000; Lee et al, 2000; Matsuoka et al, 2000). The gene discussed is TP53; the disease is neoplasm.