Low-fidelity DNA polymerase with a helicase activity that promotes microhomology-mediated end-joining (MMEJ), an alternative non-homologous end-joining (NHEJ) machinery required to repair double-strand breaks in DNA during mitosis (        ). MMEJ is an error-prone repair pathway that produces deletions of sequences from the strand being repaired and promotes genomic rearrangements, such as telomere fusions, some of them leading to cellular transformation (   ). MMEJ is required during mitosis to repair persistent double-strand breaks that originate in S-phase (, ). Although error-prone, MMEJ protects against chromosomal instability and tumorigenesis (By similarity). The polymerase acts by binding directly the 2 ends of resected double-strand breaks, allowing microhomologous sequences in the overhangs to form base pairs ( , ). It then extends each strand from the base-paired region using the opposing overhang as a template ( , ). Requires partially resected DNA containing 2 to 6 base pairs of microhomology to perform MMEJ ( , ). The polymerase lacks proofreading activity and is highly promiscuous: unlike most polymerases, promotes extension of ssDNA and partial ssDNA (pssDNA) substrates ( ). When the ends of a break do not contain terminal microhomology must identify embedded complementary sequences through a scanning step . Also shows endonuclease activity, which is required to trim the 3' ends before synthesis can occur, thereby preventing non-paired tails . Also acts as a DNA helicase, promoting dissociation of the replication protein A complex (RPA/RP-A), composed of RPA1, RPA2 and RPA3, from resected double-strand breaks to allow their annealing and subsequent joining by MMEJ . Removal of RPA/RP-A complex proteins prevents RAD51 accumulation at resected ends, thereby inhibiting homology-recombination repair (HR) pathway (, ). Also shows RNA-directed DNA polymerase activity to mediate DNA repair in vitro; however this activity needs additional evidence in vivo . May also have lyase activity . Involved in somatic hypermutation of immunoglobulin genes, a process that requires the activity of DNA polymerases to ultimately introduce mutations at both A/T and C/G base pairs (By similarity). POLQ-mediated end joining activity is involved in random integration of exogenous DNA hampers .
Subcellular locations: Nucleus, Chromosome
Enriched in chromatin in response to ultaviolet (UV) light (, ). Binds to chromatin during early G1 . Recruited to DNA damage sites, such as double-stranded breaks (DSBs), following interaction with TOPBP1 and RHNO1 (, ).
Highly expressed in testis.