DFF, A HETERODIMERIC PROTEIN THAT FUNCTIONS DOWNSTREAM OF CASPASE-3 TO TRIGGER DNA FRAGMENTATION DURING APOPTOSIS

We have identified and purified from HeLa cytosol a protein that induc es DNA fragmentation in coincubated nuclei after it is activated by ca spase-3. This protein, designated DNA Fragmentation Factor (DFF), is a heterodimer of 40 kDa and 45 kDa subunits. The amino acid sequence of the 45 kDa subunit, determined from its cDNA sequence, reveals it to be a novel protein. Caspase-3 cleaves the 45 kDa subunit at two sites to generate an active factor that produces DNA fragmentation without f urther requirement for caspase-3 or other cytosolic proteins. In cells undergoing apoptosis, the 45 kDa subunit is cleaved in the same patte rn as it is cleaved by caspase-3 in vitro. These data delineate a dire ct signal transduction pathway during apoptosis: caspase-3 to DFF to D NA fragmentation.