THE N-TERMINUS OF ANTIZYME PROMOTES DEGRADATION OF HETEROLOGOUS PROTEINS

Regulated degradation of ornithine decarboxylase (ODC) is mediated by its association with the inducible protein antizyme. The N terminus of antizyme (NAZ), although unneeded for the interaction with ODC, must be present to induce degradation. We report here that covalently graft ing NAZ to ODC confers lability that normally results from the non-cov alent association of native antizyme and ODC. To determine whether NAZ could act similarly as a modular functional domain when grafted to ot her proteins, we fused it to a region of cyclin B (amino acids 13-90) capable of undergoing degradation or to cyclin B (amino acids 13-59), which is not subject to degradation. The association with NAZ made bot h NAZ-cyclin B13-90 and NAZ-cyclin B13-59 unstable. Furthermore, NAZ a nd cyclin B 13-59 were together able to induce in vitro degradation of Trypanosoma brucei ODC, a stable protein. The ODC-antizyme complex bo und to the 26 S protease but not the 20 S proteasome, consistent with the observation that ODC degradation is mediated by the 26 S protease. The association was shown to be independent of NAZ, suggesting that N AZ does not act as a recognition signal.