Murine L929 cells were maintained in Joklik's minimal essential medium supplemented to contain 10% fetal bovine serum (FBS), 2 mM L-glutamine, 100 U/ml penicillin, 100 mg/ml streptomycin, and 25 ng/ml amphotericin B (Invitrogen). Wild-type and Biddeficient MEFs were maintained in Dulbecco's minimal essential medium (DMEM) supplemented to contain 10% FBS, 2 mM Lglutamine, 100 U/ml penicillin, 100 mg/ml streptomycin, and 25 ng/ml amphotericin B. TRAIL-R-deficient MEFs, prepared from D13 embryos, were maintained in DMEM supplemented to contain 10% FBS, 2 mM L-glutamine, 16 MEM nonessential amino acids, 0.1 mM 2-mercaptoethanol, 20 mM HEPES, 100 U/ ml penicillin, 100 mg/ml streptomycin, and 25 ng/ml amphotericin B. Reovirus strain T3D is a laboratory stock. T3SA+ was generated by reassortment of reovirus strains T1L and type 3 clone 44-MA as described [84] . Purified reovirus virions were generated from second-or third-passage L-cell lysate stocks of twice-plaque-purified reovirus [85] . Viral particles were Freon-extracted from infected cell lysates, layered onto 1. 