摘要：

We describe here the characterization of the so far identified family , , , , and . The family genes are found to be expressed with different tissue specificities and suggested to play unique physiological roles. All the recombinant are shown to be Ca(2+)/Mg(2+)-dependent and catalyze DNA hydrolysis to produce 3'-OH/5'-P ends. High activities for , , and are observed under neutral conditions, whereas shows its maximum activity at acidic pH. These enzymes have also some other peculiarities: different sensitivities to G-, aurintricarboxylic acid, and metal ions are observed. Using a transient expression system in HeLa S3 cells, the possible involvement of the in was examined. The ectopic expression of each has no toxic effect on the cells; however, extensive DNA fragmentation is observed only in -transfected cells after the . Furthermore, is revealed to be located at the perinuclear region in living cells, and to translocate into the during . Our results demonstrate that , , , and have similar but unique activities, and that among family , is capable of producing apoptotic DNA fragmentation in mammalian cells.

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