One typical biochemical processes of programmed cell death (apoptosis) is the degradation of DNA takes place in two successive stages. Degradation fragments of chromatin to oligonukleosomowych is preceded by cutting the chromosome fragments with a length of 50 (or more) of thousands of base pairs. The DNA fragmentation is associated chromatin condensation observed in cells undergoing apoptosis. One of the nuclease responsible for DNA fragmentation during apoptosis is DFF40/CAD. DFF40/CAD nuclease activation is catalyzed by caspase-3 inhibitor nuclease degradation, protein DFF45/ICAD. Other nucleases that may be involved in apoptotic DNA fragmentation among others NUC18, DNase g DNase II. In the first step of DNA degradation may be related to the activity of DNA topoisomerase II.