Siah genes are not required for p53-mediated apoptosis (A) Thymocytes were isolated from wild-type (n = 3), Siah1a−/− (n = 2), Siah2−/− (n = 2), or p53−/− (n = 1) mice or from lethally irradiated mice (n = 2) that had been reconstituted with Siah2−/− Siah1a−/− fetal liver cells. Cell viability was assessed 24 h after gamma irradiation. Duplicate cultures from each of n mice of each genotype were analyzed. Means (± standard deviations [SD] where applicable) are shown. (B) Susceptibility to UV-induced apoptosis of the parental ES cell clone (wild type), a clone containing a random insertion of the Siah1b targeting vector (Neo control), and the Siah1b-targeted clone (Siah1b−/Y). Apoptosis was assessed 24 h after treatment. Means ± SD of triplicate assays are shown. Data are representative of three independent experiments. (C) Wild-type, Siah1a−/−, Siah1b−/Y, or Siah2−/− MEFs were infected with retrovirus expressing E1A 12S. The viability of E1A-expressing MEFs or of noninfected wild-type MEFs was assessed 24 h after treatment with doxorubicin (0.1 or 0.5 μg/ml). Means ± SD of triplicate assays are shown. Western blotting (inset) confirmed equal levels of E1A 12S expression among the genotypes.