AN APOPTOTIC ENDONUCLEASE ACTIVATED EITHER BY DECREASING PH OR BY INCREASING CALCIUM

DNA fragmentation in isolated nuclei from the murine IL3-dependent bon e marrow cell line BAF3 could be stimulated either by decreasing pH be low 6.5 or by adding mu M calcium at neutral pH, An endonuclease which could also be stimulated either by a decrease in pH, to 6.5, or by th e presence of mu M calcium at neutral pH, was purified 10(4)-fold from nuclei of BAF3 cells. Digestion of DNA with the purified enzyme resul ted in 5'-terminal hydroxyl and 3'-terminal phosphate ends, These char acteristics are distinct from those described for other mammalian endo nucleases. The possible role of this enzyme in genome digestion during apoptosis is discussed.