H2ax^−/−p53^−/−Rag2^−/− mice develop thymic lymphomas with p53 inactivation. (A) Schematic of the p53⁺ allele. The relative locations of where the 11 exons of p53 are located within the 20-kb EcoRI genomic fragment. The location of the 400-bp AvaI (A) and the p53 last exon (B) probes used for Southern blotting are indicated by black rectangles. (B) Southern blot analysis of EcoRI-digested genomic DNA isolated from 6 H2ax^−/−p53^−/−Rag2^−/− thymic lymphomas and a p53^−/− mouse-tail probed with either probe A or B. The fragments corresponding to the p53⁺ alleles are indicated. (C) Western blot analysis of protein isolated from 4 H2ax^−/−p53^−/−Rag2^−/− thymic lymphomas and p53^−/− or p53^−/− control cells using either an anti-p53 antibody or an anti-H4 histone antibody as a loading control.