POLY(ADP-RIBOSE) POLYMERASE NULL MOUSE CELLS SYNTHESIZE ADP-RIBOSE POLYMERS

Poly(ADP-ribose) polymerase (PARP) (EC 2.4.2.30), the only enzyme know n to synthesize ADP-ribose polymers from NAD(+), is activated in respo nse to DNA strand breaks and functions in the maintenance of genomic i ntegrity. Mice homozygous for a disrupted gene encoding PARP are viabl e but have severe sensitivity to gamma-radiation and alkylating agents . We demonstrate here that both 3T3 and primary embryo cells derived f rom PARP(-/-) mice synthesized ADP-ribose polymers following treatment with the DNA-damaging agent, N-methyl-N'-nitro-N-nitrosoguanidine, de spite the fact that no PARP protein was detected in these cells. ADP-r ibose polymers isolated from PARP(-/-) cells were indistinguishable fr om that of PARP(+/+) cells by several criteria. First, they bound to a boronate resin selective for ADP-ribose polymers. Second, treatment o f polymers with snake venom phosphodiesterase and alkaline phosphatase yielded ribosyladenosine, a nucleoside diagnostic for the unique ribo syl-ribosyl linkages of ADP-ribose polymers. Third, they were digested by treatment with recombinant poly(ADP-ribose) glycohydrolase, an enz yme highly specific for ADP-ribose polymers, Collectively, these data demonstrate that ADP-ribose polymers are formed in PARP(-/-) cells in a DNA damage-dependent manner. Because the PARP gene has been disrupte d, these results suggest the presence of a previously unreported activ ity capable of synthesizing ADP-ribose polymers in PARP(-/-) cells.