Multiple Forms of Nuclear Deoxyribonuclease in Rat Thymocytes

Abstract

Three distinct endonucleases (DNase α, β and γ) were isolated from rat thymocyte nuclei. These three DNases differed in chromatographic behaviors and in apparent molecular masses. The cognate form of acidic DNases α and β did not require divalent cations for their activities, whereas DNase γ was a neutral endonuclease that required both Ca2+ and Mg2+ for full activity and was inhibited by Zn2+. These enzymes digested HeLa S3 cell nuclear chromatin to the nucleosomal fragments characteristic of apoptosis. Interestingly, apoptotic rat thymocyte nuclei induced by γ-ray irradiation or glucocorticoid retained considerable activity of DNase γ, whereas their activities of DNases α and β were markedly reduced. These results indicate that in rat thymocytes DNase γ is involved in DNA fragmentation during apoptosis.