DNA polymerase theta (POLQ) is a ~289 kDa protein. 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. The polymerase acts by binding directly the 2 ends of resected double-strand breaks, allowing microhomologous sequences in the overhangs to form base pairs. 1. Seki, M. et al. (2003) Nucleic acids research 31, 6117-26. PMID: 145762982. Arana, ME. et al. (2008) Nucleic acids research 36, 3847-56. PMID: 185030843. Yoon, JH. et al. (2014) The Journal of biological chemistry 289, 13177-85. PMID: 246485165. Kent, T. et al. (2015) Nature structural & molecular biology 22, 230-7. PMID: 256433236. Zahn, KE. et al. (2015) Nature structural & molecular biology 22, 304-11. PMID: 257752677. Newman, JA. et al. (2015) Structure (London, England : 1993) 23, 2319-2330. PMID: 266362569. Kent, T. et al. (2016) Nucleic acids research 44, 9381-9392. PMID: 2759125210. Wang, Z. et al. (2019) The Journal of biological chemistry 294, 3909-3919. PMID: 30655289 | 
