Nuclease involved in single-strand and double-strand DNA break repair. Recruited to sites of DNA damage through interaction with poly(ADP-ribose), a polymeric post-translational modification synthesized transiently at sites of chromosomal damage to accelerate DNA strand break repair reactions. Displays apurinic-apyrimidinic (AP) endonuclease and 3'-5' exonuclease activities in vitro. Also able to introduce nicks at hydroxyuracil and other types of pyrimidine base damage. Together with PARP3, promotes the retention of the LIG4-XRCC4 complex on chromatin and accelerate DNA ligation during non-homologous end-joining (NHEJ). Interacts with LIG4. Interacts with PARP1. Interacts with XRCC4. Interacts (via KBM motif) with XRCC5 and XRCC6; promoting recruitment to DNA damage sites. Interacts with XRCC1. Localizes to DNA damage sites. Accumulates at single-strand breaks and double-strand breaks via the PBZ-type zinc fingers. The PBZ-type zinc fingers (also named CYR) mediate non-covalent poly(ADP-ribose)-binding. Poly(ADP-ribose)-binding is dependent on the presence of zinc and promotes its recruitment to DNA damage sites. The KBM (Ku-binding motif) mediates interaction with XRCC5/Ku80 and XRCC6/Ku70 and recruitment to DNA damage sites. The FHA-like domain mediates interaction with XRCC1 and XRCC4. Poly-ADP-ribosylated. In addition to binding non covalently poly(ADP-ribose) via its PBZ-type zinc fingers, the protein is also covalently poly-ADP-ribosylated by PARP1. Phosphorylated in an ATM-dependent manner upon double-strand DNA break. Belongs to the APLF family.