Tumor protein 63 (p63) acts as a sequence specific DNA binding transcriptional activator or repressor. The isoforms contain a varying set of transactivation and auto-regulating transactivation inhibiting domains thus showing an isoform specific activity. p63 in conjunction with p73 initiates p53 dependent apoptosis in response to environmental stimuli such as DNA damage and hypoxia. p63 is also involved in Notch signaling and regulation of epithelial morphogenesis. Defects in p63 are the cause of multiple ectodermal dysplasia syndromes, a group of developmental disorders affecting tissues of ectodermal origin.