The stress-activated protein kinase JNK plays an important role in the stability and activities of key regulatory proteins, including c-Jun, ATF2, and p53. To better understand mechanisms underlying the regulation of JNK activities, we studied the effect of expression of the amino-terminal JNK fragment (N-JNK; amino acids 1-206) on the stability and activities of JNK substrates under nonstressed growth conditions, as well as after exposure to hydrogen peroxide. Mouse fibroblasts that express N-JNK under tetracycline-off (tet-off) inducible promoter exhibited elevated expression of c-Jun, ATF2, and p53 upon tetracycline removal. This increased coincided with elevated transcriptional activities of p53, but not of c-Jun or ATF2, as reflected in luciferase activities of p21(Waf1/Cip1)-Luc, AP1-Luc, and Jun2-Luc, respectively. Expression of N-JNK in cells that were treated with H(2)O(2) impaired transcriptional output as reflected in a delayed and lower level of c-Jun-, limited ATF2-, and reduced p53-transcriptional activities. N-JNK elicited an increase in H(2)O(2)-induced cell death, which is p53-dependent, because it was not seen in p53 null cells yet could be observed upon coexpression of p53 and N-JNK. The ability to alter the activity of ATF2, c-Jun, and p53 and the degree of stress-induced cell death by a JNK-derived fragment identifies new means to elucidate the nature of JNK regulation and to alter the cellular response to stress.