Gap-filling polymerase involved in repair of DNA double-strand breaks by non-homologous end joining (NHEJ). Participates in immunoglobulin (Ig) light chain gene rearrangement in V(D)J recombination. a 2'-deoxyribonucleoside 5'-triphosphate + DNA(n) = diphosphate + DNA(n+1) Expressed in a number of tissues. Abundant in thymus. DPOLM has a reduced ability to distinguish dNTP and rNTP as substrates, and elongates them on DNA primer strand with a similar efficiency. It is able to polymerize nucleotides on RNA primer strands. Belongs to the DNA polymerase type-X family.