The p63 OD is 60 % homologous to the p73 OD. While
the p53 OD contains one α-helix, the crystal structure of the
p73 OD shows that this domain is stabilized by an additional
C-terminal α-helix (H2) that is evolutionarily conserved in
vertebrate p73 and p63. It has been shown that p63
and p73 interact with each other but not with p53 in vivo, even though previous in vitro studies using an OD
lacking H2 indicated only weak interactions between p63
and p73. Newer studies using an OD including H2 have
shown that p63 and p73 preferentially form heterotetramers.of homodimers (a p63 dimer bound to a p73 dimer) in vitro,
and confirmed that p53 does not form heterooligomers with
p63 and/or p73, most likely due to the dissimilarity between
the p53 and the p63/p73 OD