A novel gene PUMA (p53 upregulated modulator of apoptosis) is a target for activation by the p53 tumor-suppressor gene. p53 functions as a transcriptional activator, and influences p53-inducible genes that play a role in the induction of apoptosis in response to p53. Antisense inhibition of PUMA expression reduced the apoptotic response to p53, and PUMA is likely to play a role in mediating p53-induced cell death through the cytochrome c/Apaf-1-dependent pathway.