Poly(ADP-ribose) polymerase (EC 2.4.2.30) is a zinc-binding protein that specifically binds to a DNA strand break in a zinc-dependent manner. We describe here the cloning and expression in Escherichia coli of a cDNA fragment encoding the two putative zinc fingers (FI and FII) . Further, we demonstrated that zinc is essential for the binding of this fragment to DNA (6). These results are consistent with the presence of the duplicated motif (Cys-Xaa2-Cys-Xaa28_30-His-Xaa2-Cys)2 in the N-terminal part of the amino acid sequence of the enzyme (7-9), which may form two zinccoordinated "fingers" based on the structural motifs described for the Xenopus 5S rRNA transcription factor TFIIIA (10, 11) or steroid receptors (12)(13)(14)

The zinc‐finger DNA‐binding domain (DBD) of poly (ADP‐ribose) polymerase (PARP, EC 2.4.2.30) specifically recognizes DNA strand breaks induced by various DNA‐damaging agents in eukaryotes. This, in turn, triggers the synthesis of polymers of ADP‐ribose linked to nuclear proteins during DNA repair. The 46 kDa DBD of human PARP, and several derivatives thereof mutated in its first or second zinc‐finger, were overproduced in Escherichia coli, in CV‐1 monkey cells or in human fibroblasts to study their DNA‐binding properties, the trans‐dominant inhibition of resident PARP activity, and the consequences on DNA repair, respectively. A positive correlation was found between the in vitro DNA‐binding capacity of the recombinant DBD polypeptides and their inhibitory effect on PARP activity stimulated by the alkylating agent N‐methyl‐N′‐nitro‐N‐nitrosoguanidine (MNNG). Furthermore, overproduced wild‐type DBD blocked unscheduled DNA synthesis induced in living cells by MNNG treatment, but not that induced by UV irradiation. These results define a critical role for the second zinc‐finger of PARP for DNA single‐stranded break binding and furthermore underscore the importance for PARP to act as a critical regulatory component in the repair of DNA damage induced by alkylating agents.

Poly(ADP-ribose) polymerase (PARP) participates in the intricate network of systems developed by the eukaryotic cell to cope with the numerous environmental and endogenous genetoxic agents. Cloning of the PARP gene has allowed the development of genetic and molecular approaches to elucidate the structure and the function of this abundant and highly conserved enzyme. This article summarizes our present knowledge in this field.