p53-mediated apoptosis in baby rat kidney (BRK) cell lines transformed by E1A and p53(val135) requires a transcriptionally functional p53. Coexpression of the E1B 19K protein in BRK cell lines transformed by E1A and p53(val135) rescues cells from p53-mediated apoptosis, and this is paralleled by the absence of both lamin and poly(ADP-ribose) polymerase cleavage. Therefore, the role of interleukin 1 beta converting enzyme (ICE)-like porteases in p53-mediated, transcriptionally dependent apoptosis was investigated. The ICE-like protease CPP32 was proteolytically activated during p53-mediated apoptosis in BRK cells, and this required a transcriptionally competent p53. Substitution of the p53 transactivation domain with the transactivation domain of herpes simplex virus VP16 (VP16/p53) resulted in accelerated kinetics of both apoptosis and Bax induction. Moreover, apoptosis induced by p53, VP16/p53, and Bax was abrogated by Z-VAD.FMK, an inhibitor of ICE-like proteases. These results indicate that all apoptotic pathways downstream of p53-mediated transcription converge upon the activation of ICE-like proteases.