Fig. 1: Simplified evolutionary tree of p53 family proteins.

Vertebrates typically have three p53 family members, p53, p63, and p73, as a result of two gene duplications at the beginning of vertebrate evolution. Multiple copies as a result of independent gene duplications are also found in several invertebrate lineages. The invertebrate p53 family genes in this tree are classified solely based on the presence or absence of a SAM domain in the predicted proteins (Ensembl Metazoa release 52 and Ensembl Protists release 52), which is a characteristic feature of vertebrate p63 and p73 proteins, but absent in vertebrate p53. The genome of the Pompeii worm (Alvinella pompejana), a member of the annelid worms, has not yet been published. Comparison with the published genome of another polychaete annelid, Capitella teleta, suggests the presence of a single p53 family gene in this organism that contains an extended p63/p73-like tetramerization domain with a second helix [77] and a SAM domain. From the analysis of the chicken genome, only p63 and p73 proteins are predicted, but a p53 transcript has been verified experimentally [78]. Branch lengths in this tree do not reflect evolutionary distance. The figure has been adapted from Joerger and Fersht [1].