Fig. (1) S³⁵ wild-type procaspase 8 or procaspase 8 with mutations F355R, F356N were mixed with varying amounts of protease and analyzed by autoradiography for cleavage. Wild-type procaspase 8 incubated with HIV-PR resulted in a 41 kd band that was much less evident in the RN mutant. Results are representative of three independent experiments.