ABSTRACT
Poly(ADP-ribosyl)ation of various DNA-binding proteins constitutes one of the earliest nuclear events triggered by DNA strand breakage associated with DNA repair, DNA replication, and cell death.1-5 This post-translational modification utilizes nuclear nicotinamide adenine dinucleotide (NAD) as a substrate and is catalyzed by an expanding poly(ADP-ribose) polymerase (PARP) gene family, which now includes PARP-1, PARP-2, and PARP-3.6,7 PARP-1 (E. C. 2.4.2.30) is activated by binding to double-or single-strand DNA breaks via its two zinc fingers8,9 and undergoes extensive autopoly(ADP-ribosyl)ation in a central automodification domain through an ester linkage between poly(ADP-ribose) (PAR) homopolymers and glutamic acid
residues in this domain.8,10 PARP-2, PARP-3, and other PARP homologues account for the residual PARP activity in PARP-1-deficient cells.6,7,11 Each PARP-1 molecule has 18 to 28 automodification sites;12 and PAR chains of up to 200 residues are covalently bound mainly to PARP-1 and to other nuclear acceptor proteins. Poly(ADPribosyl)ation of nuclear proteins in response to DNA strand breakage is transient in intact cells and is restricted mostly to the potential targets located adjacent to DNA breaks.13 The half-life of PAR is only 1 to 2 min as a result of its rapid degradation by PAR glycohydrolase.14 The nuclear protein substrates of PARP-1 include histones, DNA topo I and II,15,16 DNA pol α and δ, proliferating cell nuclear antigen (PCNA), and approximately 15 components of the DNA synthesome,16 Ca2+-Mg2+-dependent endonucleases,17 as well as an increasing number of transcription factors such as p53,18,19 TFIIF, TEF-1, TBP, YY1, SP-1, and CREB.20,21 Poly(ADP-ribosyl)ation of DNA pol α and δ 22,23 and topo I and II15,24,25 modulates their activities; in most instances, such modification inhibits enzyme activity, presumably as a result of a marked decrease in affinity of the proteins for DNA caused by electrostatic repulsion between the negatively charged DNA and PAR.
