Repair polymerase. Involved in gap-filling in DNA nonhomologous end joining (NHEJ) required for double-strand break repair. Seems to conduct DNA synthesis in a stepwise distributive fashion rather than in a processive fashion as for other DNA polymerases. Preferentially acts upon short gaps formed by the alignment of linear duplexes with complementary single-strand ends. Required for filling gaps that need removal of a 5'- or 3'-terminal mismatch, however lacks nuclease activities. a 2'-deoxyribonucleoside 5'-triphosphate + DNA(n) = diphosphate + DNA(n+1) Stimulated by the interaction with the DNL4-LIF1 complex. Interacts with DNL4 subunit of the DNL4-LIF1 complex. During meiosis. Belongs to the DNA polymerase type-X family.