Poly-ADP-ribosyltransferase that mediates poly-ADP-ribosylation of proteins and plays a key role in DNA repair (PubMed:17177976, PubMed:18055453, PubMed:18172500, PubMed:19344625, PubMed:19661379, PubMed:20388712, PubMed:21680843, PubMed:22582261, PubMed:23230272, PubMed:25043379, PubMed:26344098, PubMed:26626479, PubMed:26626480, PubMed:30104678, PubMed:31796734, PubMed:32028527, PubMed:32241924, PubMed:32358582, PubMed:33186521, PubMed:34465625, PubMed:34737271). Mediates glutamate, aspartate, serine, histidine 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:19764761, PubMed:25043379, PubMed:28190768, PubMed:29954836, PubMed:35393539, PubMed:7852410, PubMed:9315851). Serine ADP-ribosylation of proteins constitutes the primary form of ADP-ribosylation of proteins in response to DNA damage (PubMed:33186521, PubMed:34874266).

Specificity for the different amino acids is conferred by interacting factors, such as HPF1 and NMNAT1 (PubMed:28190768, PubMed:29954836, PubMed:32028527, PubMed:33186521, PubMed:33589610, PubMed:34625544, PubMed:34874266). Following interaction with HPF1, catalyzes serine ADP-ribosylation of target proteins; HPF1 confers serine specificity by completing the PARP1 active site (PubMed:28190768, PubMed:29954836, PubMed:32028527, PubMed:33186521, PubMed:33589610, PubMed:34625544, PubMed:34874266). Also catalyzes tyrosine ADP-ribosylation of target proteins following interaction with HPF1 (PubMed:29954836, PubMed:30257210).

Following interaction with NMNAT1, catalyzes glutamate and aspartate ADP-ribosylation of target proteins; NMNAT1 confers glutamate and aspartate specificity (By similarity). 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 (H2BS6ADPr and H3S10ADPr), 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, PubMed:34465625, PubMed:34874266). HPF1 initiates serine ADP-ribosylation but restricts the polymerase activity of PARP1 in order to limit the length of poly-ADP-ribose chains (PubMed:33683197, PubMed:34732825, PubMed:34795260).

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-ribosylation of a number of proteins, including itself, APLF, CHFR, RPA1 and NFAT5 (PubMed:17396150, PubMed:19764761, PubMed:24906880, PubMed:34049076). 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). PARP1-mediated DNA repair in neurons plays a role in sleep: senses DNA damage in neurons and promotes sleep, facilitating efficient DNA repair (By similarity).

In addition to DNA repair, also involved in other processes, such as transcription regulation, programmed cell death, membrane repair, adipogenesis and innate immunity (PubMed:15607977, PubMed:17177976, PubMed:19344625, PubMed:27256882, PubMed:32315358, PubMed:32844745, PubMed:35124853, PubMed:35393539, PubMed:35460603). Acts as a repressor of transcription: binds to nucleosomes and modulates chromatin structure in a manner similar to histone H1, thereby altering RNA polymerase II (PubMed:15607977, PubMed:22464733). Acts both as a positive and negative regulator of transcription elongation, depending on the context (PubMed:27256882, PubMed:35393539).

Acts as a positive regulator of transcription elongation by mediating poly-ADP-ribosylation of NELFE, preventing RNA-binding activity of NELFE and relieving transcription pausing (PubMed:27256882). Acts as a negative regulator of transcription elongation in response to DNA damage by catalyzing poly-ADP-ribosylation of CCNT1, disrupting the phase separation activity of CCNT1 and subsequent activation of CDK9 (PubMed:35393539). Involved in replication fork progression following interaction with CARM1: mediates poly-ADP-ribosylation at replication forks, slowing fork progression (PubMed:33412112).

Poly-ADP-ribose chains generated by PARP1 also play a role in poly-ADP-ribose-dependent cell death, a process named parthanatos (By similarity). Also acts as a negative regulator of the cGAS-STING pathway (PubMed:32315358, PubMed:32844745, PubMed:35460603). Acts by mediating poly-ADP-ribosylation of CGAS: PARP1 translocates into the cytosol following phosphorylation by PRKDC and catalyzes poly-ADP-ribosylation and inactivation of CGAS (PubMed:35460603).

Acts as a negative regulator of adipogenesis: catalyzes poly-ADP-ribosylation of histone H2B on 'Glu-35' (H2BE35ADPr) following interaction with NMNAT1, inhibiting phosphorylation of H2B at 'Ser-36' (H2BS36ph), thereby blocking expression of pro-adipogenetic genes (By similarity). 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)

Homodimer; PARP-type zinc-fingers from separate PARP1 molecules form a dimer module that specifically recognizes DNA strand breaks (PubMed:22683995). Heterodimer; heterodimerizes with PARP2 (By similarity). Interacts (via the PARP catalytic domain) with HPF1 (PubMed:27067600, PubMed:28190768, PubMed:29954836, PubMed:32028527, PubMed:33589610).

Interacts with NMNAT1 (By similarity). Interacts with nucleosomes; with a preference for nucleosomes containing H2A.X (PubMed:15607977, PubMed:31848352). 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 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).

Interacts (when auto-poly-ADP-ribosylated) with XRCC1; leading to inhibit PARP1 ADP-ribosyltransferase activity (PubMed:34102106, PubMed:34811483). Interacts with SPINDOC; promoting PARP1 ADP-ribosyltransferase activity (PubMed:34737271). Interacts with BANF1; leading to inhibit PARP1 ADP-ribosyltransferase activity in response to oxidative DNA damage (PubMed:31796734).

Interacts (when sumoylated and ubiquitinated) with VCP/p97; leading to its extraction from chromatin (PubMed:35013556). Interacts with YARS1; Interacts with PACMP micropeptide; interaction (PubMed:25533949). Interacts with PACMP micropeptide; Interacts with PACMP micropeptide; interaction (PubMed:35219381).

Interacts (when poly-ADP-ribosylated) with isoform 1 of MACROH2A1; MACROH2A1 specifically binds to poly-ADP-ribose chains and inhibits PARP1 activity, limiting the consumption of nuclear NAD(+) (By similarity). Interacts with CARM1; promoting recruitment to replication forks (PubMed:33412112). Interacts with RECQL (PubMed:35025765).

Interacts with ZNF32; the interaction reshapes ZNF432 interacting proteins (PubMed:37823600). Interacts with TPRN; TPRN interacts with a number of DNA damage response proteins, is recruited to sites of DNA damage and may play a role in DNA damage repair (PubMed:23213405)

Interacts (when auto-poly-ADP-ribosylated) with AIFM1

(Microbial infection) Interacts with human herpesvirus 8 (KSHV) protein RTA/ORF50; this interaction negatively regulates RTA/ORF50 transactivation activity

The two PARP-type zinc-fingers (also named Zn1 and Zn2) specifically recognize DNA strand breaks: PARP-type zinc-finger 1 binds PARP-type zinc-finger 2 from a separate PARP1 molecule to form a dimeric module that specifically recognizes DNA strand breaks

The PADR1-type (also named Zn3) zinc-finger mediates an interdomain contact and is required for the ability of PARP1 to regulate chromatin structure

The BRCT domain is able to bind intact DNA without activating the poly-ADP-ribosyltransferase activity (PubMed:34919819). The BRCT domain mediates DNA intrastrand transfer (named 'monkey-bar mechanism') that allows rapid movements of PARP1 through the nucleus (PubMed:34919819)

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

The PARP alpha-helical domain (also named HD region) prevents effective NAD(+)-binding in absence of activation signal (PubMed:26626479, PubMed:26626480). Binding to damaged DNA unfolds the PARP alpha-helical domain, relieving autoinhibition (PubMed:26626479, PubMed:26626480)