Figure 2.

Ubiquitination independent function of MDM2: the antirepression model of p53 activation. Under homeostasis, p53 is kept in a preset repressed state when staying in the same complex with MDM2 and MDMX on chromatin. When p53 acetylation is fully activated, the recruitments of MDM2 and MDMX on those p53 target promoters will be abrogated due to the decreased association between the acetylated form of p53 and MDM2/MDMX. p53 is then released from the originally repressed status, and this step is designated as antirepression step in this modified p53 activation model. Ac = acetylation.