FIGURE 4

Mitochondrial factors are not able to induce caspase activation in S2 cell lysate. (a) S100 from 2 10⁹ untreated S2 cells was incubated with S100 from 1 10⁸ S2 cells that were untreated, treated with dronc and/or cytochrome c dsRNA, or treated with dronc dsRNA and UV irradiated. An immunoblot was performed for DrICE (left) and caspase activity was determined using Ac-DEVD-afc as substrate (right). (b) DrICE immunoblot (left) and caspase activity assay using DEVD-afc (right) of the following samples: lane 1, nonincubated S100 from untreated S2 cells; lane 2, S100 from untreated S2 cells that was incubated alone; lanes 3–8, S100 from untreated S2 cells that was incubated with the indicated fractions from S2 cells that were UV irradiated or treated with dronc and cytochrome c dsRNA and UV irradiated; lane 9, S100 from untreated cells that was incubated with lysed P10 fraction; lane 10, S100 from untreated cells that was incubated with cytochrome c protein and dATP