This application describes the cloning of p63, a gene at chromosome 3q27-29, that bears homology to the tumor suppressor p53. The p63 gene encodes at least six different isotypes. p63 was detected in a variety of human and mouse tissue and demonstrates remarkably divergent activities, such as the ability to transactivate p53 reporter genes and induce apoptosis. Isotopes of p63 lacking a transactivation domain act as dominant negatives towards the transactivation by p53 and p63.