Mdm2 has been shown to regulate p53 stability by targeting the p53 protein for proteasomal
degradation. We now report that Mdm2 is a ubiquitin protein ligase (E3) for p53 and that its
activity is dependent on its RING finger. Furthermore, we show that Mdm2 mediates its own
ubiquitination in a RING finger-dependent manner, which requires no eukaryotic proteins
other than ubiquitin-activating enzyme (E1) and an ubiquitin-conjugating enzyme (E2). It is
apparent, therefore, that Mdm2 manifests an intrinsic capacity to mediate ubiquitination …