p53ER^TAM stability in Mdm2-and Arf-overexpressing cells. (A) Immunoblotting detecting p53ER^TAM in cycloheximide (CHX)–treated Mp53ER^RES cells in the absence (left panel) and the presence (right panel) of 4OHT. (B) Immunoblotting detecting Arf in Mp53ER^RES cells infected with the control (“vector”) and the Arf-transducing (“Arf”) retroviruses. (C) Immunoblotting detecting p53ER^TAM in the same cultures. Where indicated, cells were pretreated with 4OHT for 3 hours. (D) Selection against Arf-overexpressing Mp53ER^RES cells in mixed cultures. When indicated, 4OHT was added on day 2 after infection.