Caspase-3 is a widely expressed dimeric peptidase that is the major executioner caspase, the primary downstream mediator of apoptotic-associated proteolysis. Caspase-3 cleaves multiple substrates including PARP, proIL-16, PKC-gamma and -delta, proCaspases-6, -7, and -9, and beta-Catenin. Normally, it is an inactive, exclusively cytosolic homodimer. During apoptosis, however, proCaspase-3 is activated by cleavage into p20 and p12 subunits, and the p20 subunit is trimmed to yield a p17 subunit. Active Caspase-3 contains two p17 and two p12 subunits.