Poly-ADP-ribosyltransferase that mediates poly-ADP-ribosylation of proteins and plays a key role in DNA repair (PubMed:17177976, PubMed:18172500, PubMed:19344625, PubMed:19661379, PubMed:21680843, PubMed:23230272, PubMed:25043379, PubMed:33186521, PubMed:32028527, PubMed:26344098). Mediates glutamate, aspartate, serine or tyrosine ADP-ribosylation of proteins: the ADP-D-ribosyl group of NAD(+) is transferred to the acceptor carboxyl group of target residues and further ADP-ribosyl groups are transferred to the 2'-position of the terminal adenosine moiety, building up a polymer with an average chain length of 20-30 units (PubMed:7852410, PubMed:9315851, PubMed:19764761, PubMed:25043379, PubMed:28190768, PubMed:29954836). Serine ADP-ribosylation of proteins constitutes the primary form of ADP-ribosylation of proteins in response to DNA damage (PubMed:33186521). Mainly mediates glutamate and aspartate ADP-ribosylation of target proteins in absence of HPF1 (PubMed:19764761, PubMed:25043379). Following interaction with HPF1, catalyzes serine ADP-ribosylation of target proteins; HPF1 conferring serine specificity by completing the PARP1 active site (PubMed:28190768, PubMed:29954836, PubMed:33186521, PubMed:32028527). Also catalyzes tyrosine ADP-ribosylation of target proteins following interaction with HPF1 (PubMed:30257210, PubMed:29954836). PARP1 initiates the repair of DNA breaks: recognizes and binds DNA breaks within chromatin and recruits HPF1, licensing serine ADP-ribosylation of target proteins, such as histones, thereby promoting decompaction of chromatin and the recruitment of repair factors leading to the reparation of DNA strand breaks (PubMed:17177976, PubMed:18172500, PubMed:19344625, PubMed:19661379, PubMed:23230272, PubMed:27067600). In addition to base excision repair (BER) pathway, also involved in double-strand breaks (DSBs) repair: together with TIMELESS, accumulates at DNA damage sites and promotes homologous recombination repair by mediating poly-ADP-ribosylation (PubMed:26344098, PubMed:30356214). Mediates the poly(ADP-ribosyl)ation of a number of proteins, including itself, APLF and CHFR (PubMed:17396150, PubMed:19764761). In addition to proteins, also able to ADP-ribosylate DNA: catalyzes ADP-ribosylation of DNA strand break termini containing terminal phosphates and a 2'-OH group in single- and double-stranded DNA, respectively (PubMed:27471034). Required for PARP9 and DTX3L recruitment to DNA damage sites (PubMed:23230272). PARP1-dependent PARP9-DTX3L-mediated ubiquitination promotes the rapid and specific recruitment of 53BP1/TP53BP1, UIMC1/RAP80, and BRCA1 to DNA damage sites (PubMed:23230272). Acts as a regulator of transcription: positively regulates the transcription of MTUS1 and negatively regulates the transcription of MTUS2/TIP150 (PubMed:19344625). Plays a role in the positive regulation of IFNG transcription in T-helper 1 cells as part of an IFNG promoter-binding complex with TXK and EEF1A1 (PubMed:17177976). Involved in the synthesis of ATP in the nucleus, together with NMNAT1, PARG and NUDT5 (PubMed:27257257). Nuclear ATP generation is required for extensive chromatin remodeling events that are energy-consuming (PubMed:27257257). NAD(+) + (ADP-D-ribosyl)n-acceptor = nicotinamide + (ADP-D-ribosyl)n+1-acceptor + H(+). L-seryl-[protein] + NAD(+) = H(+) + nicotinamide + O-(ADP-D-ribosyl)-L-seryl-[protein] L-aspartyl-[protein] + NAD(+) = 4-O-(ADP-D-ribosyl)-L-aspartyl-[protein] + nicotinamide L-glutamyl-[protein] + NAD(+) = 5-O-(ADP-D-ribosyl)-L-glutamyl-[protein] + nicotinamide L-tyrosyl-[protein] + NAD(+) = H(+) + nicotinamide + O-(ADP-D-ribosyl)-L-tyrosyl-[protein] kcat is 390 sec(-1) for NAD(+). Homo- and heterodimer with PARP2. Interacts with APTX (PubMed:15044383). Component of a base excision repair (BER) complex, containing at least XRCC1, PARP1, PARP2, POLB and LRIG3 (By similarity). Interacts with SRY (PubMed:16904257). The SWAP complex consists of NPM1, NCL, PARP1 and SWAP70 (By similarity). Interacts with TIAM2 (By similarity). Interacts with PARP3; leading to activate PARP1 in absence of DNA (PubMed:20064938). Interacts (when poly-ADP-ribosylated) with CHD1L (via macro domain) (PubMed:19661379, PubMed:29220653). Interacts with the DNA polymerase alpha catalytic subunit POLA1; this interaction functions as part of the control of replication fork progression (PubMed:9518481). Interacts with EEF1A1 and TXK (PubMed:17177976). Interacts with RNF4 (PubMed:19779455). Interacts with RNF146 (PubMed:21799911). Interacts with ZNF423 (PubMed:22863007). Interacts with APLF (PubMed:17396150). Interacts with SNAI1 (via zinc fingers); the interaction requires SNAI1 to be poly-ADP-ribosylated and non-phosphorylated (active) by GSK3B (PubMed:21577210). Interacts (when poly-ADP-ribosylated) with PARP9 (PubMed:23230272). Interacts with NR4A3; activates PARP1 by improving acetylation of PARP1 and suppressing the interaction between PARP1 and SIRT1 (By similarity). Interacts (via catalytic domain) with PUM3; the interaction inhibits the poly-ADP-ribosylation activity of PARP1 and the degradation of PARP1 by CASP3 following genotoxic stress (PubMed:21266351). Interacts (via the PARP catalytic domain) with HPF1 (PubMed:27067600, PubMed:28190768, PubMed:29954836, PubMed:32028527). Interacts with ZNF365 (PubMed:23966166). Interacts with RRP1B (PubMed:19710015). Interacts with TIMELESS; the interaction is direct (PubMed:26344098). Interacts with CGAS; leading to impede the formation of the PARP1-TIMELESS complex (PubMed:30356214). Interacts with KHDC3L, the interaction is increased following the formation of DNA double-strand breaks (PubMed:31609975). Localizes to sites of DNA damage. The N-terminal disordered region does not act as a key DNA-binding domain. The WGR and PARP catalytic domains function together to recruit PARP1 to sites of DNA breaks. The N-terminal disordered region is only required for activation on specific types of DNA damage. The WGR domain bridges two nucleosomes, with the broken DNA aligned in a position suitable for ligation. The bridging induces structural changes in PARP1 that signal the recognition of a DNA break to the catalytic domain of PARP1, promoting HPF1 recruitment and subsequent activation of PARP1, licensing serine ADP-ribosylation of target proteins. Poly-ADP-ribosylated on glutamate and aspartate residues by autocatalysis (PubMed:19764761). Poly-ADP-ribosylated by PARP2; poly-ADP-ribosylation mediates the recruitment of CHD1L to DNA damage sites (PubMed:19661379). ADP-ribosylated on serine by autocatalysis; serine ADP-ribosylation takes place following interaction with HPF1 (PubMed:28190768). Auto poly-ADP-ribosylated on serine residues, leading to dissociation of the PARP1-HPF1 complex from chromatin (By similarity). Mono-ADP-ribosylated at Lys-521 by SIRT6 in response to oxidative stress, promoting recruitment to double-strand breaks (DSBs) sites (PubMed:21680843, PubMed:22753495, PubMed:27568560). Phosphorylated by PRKDC (PubMed:10467406). Phosphorylated by TXK (PubMed:17177976). S-nitrosylated, leading to inhibit transcription regulation activity. Belongs to the ARTD/PARP family. Catalysis - Issue 235 of April 2021