Chromatin condensation and nuclear fragmentation (CCNF) are the hallmarks of apoptosis. CCNF is triggered by the activation of members of the caspase family, caspase activated DNase (CAD/DFF40), and several novel proteins including AIF and CIDE. A new inducer of chromatin condensation was recently identified and designated Acinus (for apoptotic chromatin condensation inducer in the nucleus). Acinus is cleaved by Caspase 3 and an additional unknown protease generating a small active peptide p17, which causes chromatin condensation in vitro when it is added to purified nuclei. Acinus also induces apoptotic chromatin condensation in cells. Acinus is ubiquitously expressed. Three different spliced forms of Acinus have been identified in human and mouse and designated Acinus L (1341 amino acids), Acinus S (583 amino acids) and Acinus S' (614 amino acids)