Polynucleotide : adenosine glycosidase activity of saporin-L1: effect on various forms of mammalian DNA

Saporin-L1 from the leaves of Saponaria officinalis belongs to a group of p lant polynucleotide:adenosine glycosidases, known as ribosome-inactivating proteins due to their property of depurinating the major rRNA. Previous exp eriments indicated that saporin-L1 and other ribosome-inactivating proteins depurinate also DNA [Barbieri et al. (1994) Nature 372, 324; and (1996) Bi ochem. J. 319, 507-513]. Here we describe the effects of highly purified nu clease-free saporin-L1 on mammalian nuclear and mitochondrial DNA. Saporin- L1 had less activity on mitochondrial DNA than on nuclear DNA. A low, altho ugh significant, depurination of both chromatin and whole nuclei was observ ed. Mitochondrial nucleic acids are heavily depurinated in intact mitochond ria, although the contribute of mtDNA to the deadenylation events is not kn own. The kinetic constants for several substrates were determined. (C) 2000 Elsevier Science B.V. All rights reserved.