Poly(ADP-ribose) polymerase 1 regulates activity of DNA polymerase beta in long patch base excision repair.

Poly(ADP-ribose)polymerase 1 (PARP1), functioning as DNA nick-sensor, interacts with base excision repair (BER) DNA intermediates containing single-strand breaks. When bound to DNA breaks, PARP1 catalyzes synthesis of poly(ADP-ribose) covalently attached to itself and some nuclear proteins. Autopoly(ADP-ribosyl)ation of PARP1 facilitates its dissociation from DNA breaks and is considered as a factor regulating DNA repair. In the study, using system reconstituted from purified BER proteins, bovine testis nuclear extract and model BER DNA intermediates, we examined the influence of PARP1 and its autopoly(ADP-ribosyl)ation on DNA polymerase beta (Pol beta)-mediated long patch (LP) BER DNA synthesis that is accomplished through a cooperation between Pol beta and apurinic/apyrimidinic endonuclease1 (APE1) or flap endonuclease 1 (FEN1) and gap-filling activity of Pol beta. PARP1 upon interaction with nicked LP BER DNA intermediated, formed after gap-filling, was shown to suppress the subsequent steps in LP pathway. PARP1 interferes with APE1-dependent stimulation of DNA synthesis by Pol beta via strand-displacement mechanism. PARP1 also represses Pol beta/FEN1-mediated LP BER DNA synthesis via a "gap translation" mechanism inhibiting FEN1 activity on the nicked DNA intermediate. Poly(ADP-ribosyl)ation of PARP1 abolishes its inhibitory influence on LP BER DNA synthesis catalyzed by Pol beta both via APE1-mediated strand-displacement and FEN1-mediated "gap translation" mechanism. Thus PARP1 may act as a negative regulator of Pol beta activity in LP BER pathway and poly(ADP-ribosyl)ation of PARP1 seems to play a critical role in enablement of Pol beta-mediated DNA synthesis in this process. In contrast, interaction of PARP1 with one nucleotide gapped DNA mimicking the intermediate of short patch (SP) BER slightly inhibits the gap-filling activity of Pol beta and the overall efficiency of SP BER is practically unaffected by PARP1. Thus, PARP1 differentially influences DNA synthesis in SP- and LP BER pathways.