Inhibits p53/TP53- and TP73/p73-mediated cell cycle arrest and apoptosis by binding its transcriptional activation domain. Inhibits degradation of MDM2. Can reverse MDM2-targeted degradation of TP53 while maintaining suppression of TP53 transactivation and apoptotic functions.Region I is sufficient for binding TP53 and inhibiting its G1 arrest and apoptosis functions. It also binds TP73. Region II contains most of a central acidic region and a putative C4-type zinc finger. The RING finger domain which coordinates two molecules of zinc mediates the heterooligomerization with MDM2.