Mdm2 is a ubiquitin ligase that promotes polyubiquitination of unphosphorylated p53. p53 is targeted to the proteasome where it is degraded. When p53 is phosphorylated, Mdm2 dissociates from p53.

A) Mdm2 stabilizes phosphorylated p53.
B) Mdm2 degrades phosphorylated p53.
C) Phosphorylation of p53 inhibits its degradation by Mdm2.
D) Mdm2 has no role in the degradation of p53.