DNA-binding protein involved in single-strand DNA break repair, double-strand DNA break repair and base excision repair. Resolves abortive DNA ligation intermediates formed either at base excision sites, or when DNA ligases attempt to repair non-ligatable breaks induced by reactive oxygen species. Catalyzes the release of adenylate groups covalently linked to 5'-phosphate termini, resulting in the production of 5'-phosphate termini that can be efficiently rejoined (PubMed:16964241). Also able to hydrolyze adenosine 5'-monophosphoramidate (AMP-NH(2)) and diadenosine tetraphosphate (AppppA), but with lower catalytic activity (By similarity). Likewise, catalyzes the release of 3'-linked guanosine (DNAppG) and inosine (DNAppI) from DNA, but has higher specific activity with 5'-linked adenosine (AppDNA) (By similarity). a 5'-end adenosine-5'-diphospho-5'-(2'-deoxyribonucleoside)-DNA + H2O = a 5'-end 5'-monophospho-2'-deoxyribonucleoside-DNA + AMP + 2 H(+) a 5'-end adenosine-5'-diphospho-5'-ribonucleoside-2'-deoxyribonucleotide-DNA + H2O = a 5'-end 5'-monophospho-ribonucleoside-2'-deoxyribonucleotide-DNA + AMP + 2 H(+) a 3'-end 2'-deoxyribonucleotide-3'-diphospho-5'-guanosine-DNA + H2O = a 3'-end 2'-deoxyribonucleotide 3'-phosphate-DNA + GMP + 2 H(+) Interacts with single-strand break repair proteins XRCC1, XRCC4, ADPRT/PARP1 and p53/TP53. Interacts with NCL. Interacts (via FHA-like domain) with MDC1 (phosphorylated). Upon genotoxic stress, colocalizes with XRCC1 at sites of DNA damage. Colocalizes with MDC1 at sites of DNA double-strand breaks. Interaction with NCL is required for nucleolar localization (By similarity). Widely expressed. Expressed in heart, liver, kidney, spleen, lung, muscle, brain stem, spinal cord, cerebellum and brain. The histidine triad, also called HIT motif, forms part of the binding loop for the alpha-phosphate of purine mononucleotide. The FHA-like domain mediates interaction with NCL; XRCC1 and XRCC4. The HIT domain is required for enzymatic activity. The C2H2-type zinc finger mediates DNA-binding.