The transcriptional activities of p53 and its homologue p51/p63: Similarities and differences

p51/p63 is a novel p53 homologue that has been shown to act as a transcript ional activator through thr p53-binding sequence of the p21/WAF1 promoter a nd to induce apoptosis when it is expressed transiently in a human tumor ce ll line. We de,eloped transcription assay systems for these two related gen es in both Saccharomyces cerevisiae and mammalian cells and used them to in vestigate the functional similarities and differences of these genes. We fo und that p51/p63 trans-activated the previously identified p53 target genes , but the degree of the transactivation by p51/p63 differed from that by p5 3, These results suggest that the cellular signal on p51/p63 cross-talks pa rtially but not completely with that of the p53 pathway.