(b) Subcellular fractionation of blood neutrophils that were left untreated to induce spontaneous apoptosis. After 4 h incubation, cleavage of Atg5 was evident and both full-length and truncated Atg5 were present in the cytosol. After 8 h incubation, some 24K Atg5 but not full-length Atg5 was found in the mitochondrial fraction. Mitochondrial association of truncated Atg5 coincided with the release of cytochrome c into the cytosol. The same data were observed in staurosporine-induced apoptosis of Jurkat cells (data not shown). C, cytosol; M, mitochondria. 