Involved in DNA single-strand break repair by mediating the assembly of DNA break repair protein complexes. Probably during DNA repair, negatively regulates ADP-ribose levels by modulating ADP-ribosyltransferase PARP1 activity. Homodimer. Interacts with polynucleotide kinase (PNK), DNA polymerase-beta (POLB) and DNA ligase III (LIG3). Interacts with APTX and APLF. Interacts with APEX1; the interaction is induced by SIRT1 and increases with the acetylated form of APEX1. Moves from the nucleoli to the global nuclear chromatin upon DNA damage. Expressed in fibroblasts, retinal pigmented epithelial cells and lymphoblastoid cells (at protein level). Phosphorylation of Ser-371 causes dimer dissociation. Phosphorylation by CK2 promotes interaction with APTX and APLF. Sumoylated. Carriers of the polymorphic Gln-399 allele may be at greater risk for tobacco- and age-related DNA damage. The disease is caused by variants affecting the gene represented in this entry.