Question: how mdm2 tags p53 for degradation?
Answer: Regulation of p53 by MDM2. p53 and MDM2 form an autoregulatory feedback loop. p53 stimulates the expression of MDM2; MDM2, in turn, inhibits p53 activity because it stimulates its degradation in the nucleus and the cytoplasm, blocks its transcriptional activity, and promotes its nuclear export.