NAD serves as a substrate for the ADP-ribosylation of proteins. In addition to the poly ADP-ribosylation of histones and other nuclear proteins by the poly (ADP-ribose) polymerase (PARP) family, mono-ADP-ribosylation reactions are catalyzed by bacterial toxins. Interestingly, the capacity is shared by pierisin-1, a peptide isolated from the late larval and early pupal stages of cabbage butterfly (Pieris rapae), which shows potent apoptogenic activity against mammalian cells. Pierisin-1 was purified as 100 kDa protein and a cDNA was cloned and in vitro synthesis achieved in a rabbit reticulocyte lysate system. Purified pierisin-1 caused 50% growth inhibition of cultured HeLa cells at only 0.043 ng/ml. The protein features an N-terminal domain with an ADP-ribosylating sequence and a C-terminal domain with binding capacity to Gb3 and Gb4 on cell surfaces, and apoptogenic activity was found to be lost on replacement of glutamic acid 165 by glutamine. Pierisin-1 ADP-ribosylated DNA but not proteins with NAD as the substrate, indicating unique ADP-ribosyltransferase activity, and transfer of ADP-ribosyl moiety to 2-amino-group of deoxyguanosine could be confirmed. Forced expression of bcl-2 in cells suppressed apoptosis caused by pierisin-1, Cytochrome c release and activation of caspases 9 and 3 were evident. At low concentration of pierisin-1 not causing apoptosis, mutations leading to G→C transversions were induced in cultured mammalian cells. The distribution of pierisin is limited to genus Pieris butterflies and mRNA and pierisin activity demonstrate peaks during the late larval and early pupal stages. The physiological function of pierisin for cabbage butterflies remains to be unveiled. A carcinostatic activity has been demonstrated in vivo.