Poly(ADP-ribose) polymerases covalently modify strand break termini in DNA fragments in vitro

Abstract

Poly(ADP-ribose) polymerases (PARPs/ARTDs) use nicotinamide adenine dinucleotide (NAD+) to catalyse the synthesis of a long branched poly(ADPribose) polymer (PAR) attached to the acceptor amino acid residues of nuclear proteins. PARPs act on single- and double-stranded DNA breaks by recruiting DNA repair factors. Here, in in vitro biochemical experiments, we found that the mammalian PARP1 and PARP2 proteins can directly ADP-ribosylate the termini of DNA oligonucleotides. PARP1 preferentially catalysed covalent attachment of ADP-ribose units to the ends of recessed DNA duplexes containing 3 -cordycepin, 5 - and 3 - phosphate and also to 5 -phosphate of a singlestranded oligonucleotide. PARP2 preferentially ADPribosylated the nicked/gapped DNA duplexes containing 5 -phosphate at the double-stranded termini. PAR glycohydrolase (PARG) restored native DNA structure by hydrolysing PAR-DNA adducts generated by PARP1 and PARP2. Biochemical and mass spectrometry analyses of the adducts suggested that PARPs utilise DNA termini as an alternative to 2 -hydroxyl of ADP-ribose and protein acceptor residues to catalyse PAR chain initiation either via the 2 ,1 -O-glycosidic ribose-ribose bond or via phosphodiester bond formation between C1 of ADPribose and the phosphate of a terminal deoxyribonucleotide. This new type of post-replicative modification of DNA provides novel insights into the molecular mechanisms underlying biological phenomena of ADP-ribosylation mediated by PARPs.