This gene is a member of the DNA polymerase type-X family and encodes a template-independent DNA polymerase that catalyzes the addition of deoxynucleotides to the 3'-hydroxyl terminus of oligonucleotide primers. In vivo, the encoded protein is expressed in a restricted population of normal and malignant pre-B and pre-T lymphocytes during early differentiation, where it generates antigen receptor diversity by synthesizing non-germ line elements (N-regions) at the junctions of rearranged Ig heavy chain and T cell receptor gene segments. Alternatively spliced transcript variants encoding different isoforms of this gene have been described. [provided by RefSeq, Jul 2008],catalytic activity: Deoxynucleoside triphosphate + DNA(n) = diphosphate + DNA(n+1).,cofactor: Magnesium., disease:Very high levels of enzyme activity have been detected in certain acute leukemic cells.,function:Template-independent DNA polymerase which catalyzes the random addition of deoxynucleoside 5'-triphosphate to the 3'-end of a DNA initiator. One of the in vivo functions of this enzyme is the addition of nucleotides at the junction (N region) of rearranged Ig heavy chain and T-cell receptor gene segments during the maturation of B- and T-cells.,similarity:Belongs to the DNA polymerase type-X family.,similarity:Contains 1 BRCT domain.,subunit:Interacts with PRP19 and DNTTIP1. Forms a ternary complex with DNTTIP2 and core histone. Released from this complex by PCNA.