Fig. 1. Loss-of-function of PARP-1 following proteolysis by caspase 3. Native () and proteolysed () PARP-1 were compared for their poly(ADP-ribosyl)ation activity in the presence of saturating concentration of co-enzymic DNA over a period of 5 minutes. The activity of native PARP-1 was also measured in the absence of DNA (). Poly(ADP-ribose) synthesis was carried out until maximal level of product could be obtained for both the cleaved and intact enzyme in order to maximize the potential re-association of the apoptotic fragments. This approach was successfully used for the reconstitution of PARP-1 activity following limited proteolysis with papain (Kameshita et al., 1986). Assays were performed in triplicate and the s.d. for each time point is shown.