The p53 protein exerts its tumor suppressive function mainly by acting as a 
transcription activator. Two transactivation domains (TADs) located at the 
amino-terminus of p53 are required for transcription activation, and the 
activity of TADs is tightly regulated by post-translational modifications, such 
as phosphorylation. We attempted to dissect the functions of the two TADs and 
phosphorylation within the TADs by analyzing p53 target genes induced by 
full-length p53 (FL-p53), N-terminally deleted p53 isoform lacking the first TAD 
(Delta1stTAD) and p53 carrying point mutations at all serine residues within the 
two TADs (TAD-S/A). By performing a comprehensive survey by employing microarray 
expression analysis, the induction of target genes by FL-p53, Delta1stTAD and 
TAD-S/A was analyzed. All p53s showed different target gene induction patterns, 
suggesting the importance of the two TADs and phosphorylation within the TADs in 
target gene induction. Although Delta1stTAD showed a marked decrease in the 
ability to induce genes induced by FL-p53, Delta1stTAD induced many 
apoptosis-related genes that were not induced by FL-p53, suggesting the roles of 
these Delta1stTAD-induced genes in Delta1stTAD-dependent apoptosis. 
Approximately 80% of genes induced by FL-p53 were not induced by TAD-S/A, 
including 29 previously reported p53 target genes such as Hdm2 and Bax, 
emphasizing the importance of phosphorylation within the TADs. These results 
demonstrate the significance of the regulation and differential roles of the 
N-terminal TADs in p53 transcriptional activity.