Fig. 1. A, the structure of Mdm2 and the position of the mutants used in this study are shown. B, Western blot analysis of Mdm2 and p53 protein levels after cotransfection into U2OS cells. Wild-type p53 was cotransfected with each of the indicated Mdm2 mutants and a plasmid expressing GFP to demonstrate equal transfection efficiencies. Arrows show Mdm2 proteins. C, Western blot analysis of p53 and Mdm2 levels after cotransfection of wild-type Mdm2 or the Mdm2 point mutant 464Ala with wild-type p53 into U2OS cells.