摘要：

The physiological and pathological importance of cell death by apoptosis has recently been recognized. One of the hallmarksof apoptosis is the enzymatic cleavage of genomic DNA into nucleosomal oligomers. The identification of an endonuclease responsiblefor apoptosis might help to explain how this cell suicide is regulated and why DNA is cleaved. Here, we found that γ typeof DNase was retained in apoptotic rat thymocyte nuclei. Homogeneously purified DNase γ (Mr = 33 kDa) from the apoptotic nuclei was revealed to be a Ca²⁺/Mg²⁺-dependent endonuclease and inhibited by Zn²⁺. This enzyme cleaved chromosomal DNA with 3′-hydroxyl (OH) and 5′-phosphoryl (P) ends. The cleavage ends and its divalent cation dependencies match those observed in apoptotic thymocytes induced by X-irradiationor glucocorticoid treatment, indicating that this endonuclease is a central component of the thymic apoptosis machi

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