An endonuclease responsible for apoptosis.

Apoptosis is a form of cell death that plays important roles in physiological and pathological phenomena as diverse as embryogenesis, metamorphosis, hemopoiesis, and carcinogenesis (Kerr et al. 1972; Wyllie 1980; Berger 1985; Carson et al. 1986; Ucker 1987; Smith et al. 1989; Dive and Hickman 1991; Groux et al. 1992; Cohen et al. 1992; Tanuma et al. 1993). Although apoptosis is thought to be a gene-directed cell death, how this suicide is regulated is still unknown. Apoptosis is characterized morphologically by cell shrinkage, nuclear collapse, and cell fragmentation, known as apoptotic bodies, which is accompanied by internucleosomal DNA fragmentation (Kerr et al. 1972; Wyllie 1980). The signal transduction and determination processes in apoptosis initiated by apoptotic signals are complex and dependent on cell types and states. However, the DNA fragmentation, which is suggested to be catalyzed by a constitutive endonuclease, is a crucial process common in apoptosis, irrespective of the initial stimulus.