Figure 2. Analysis of the protein interaction domains. H1299 cells were transfected for 24 h with plasmids producing the indicated Flag-tagged fragments of p65RelA plus MDM2 (A) or with plasmids expressing the depicted MDM2 fragments plus full-length p65 (B). Cell extracts were incubated with anti-Flag or anti-p65 antibodies to immuno/co-immunoprecipitate the transfected proteins, and the precipitates were analyzed by western blotting with the indicated antibodies. Note that Flag-p65-Cterm was only weakly expressed (A, lane 4). RHD, Rel homology domain; TAD, transactivation domain; p53, p53-binding domain; A/Z, acidic and zinc finger domains; R, RING domain.