Terminal deoxynucleotidyl transferase

Terminal Deoxynucleotidyl Transferase, also known as TdT and terminal transferase, is a specialized DNA polymerase expressed in immature, pre-B, pre-T lymphoid cells, and acute lymphoblastic leukemia/lymphoma cells. TdT adds N-nucleotides to the variable, diversity, and joining exons during antibody gene recombination.

TdT catalyses the addition of nucleotides to the 3' terminus of a DNA molecule. Unlike most DNA polymerases it does not require a template. The preferred substrate of this enzyme is a proturbing 3' overhang, but it can also add nucleotides to blunt or recessed 3' ends. Cobalt is a necessary cofactor.

Terminal transferase has applications in molecular biology. It can be used in RACE to add nucleotides which can then be used as a template for a primer in subsequent PCR. It can also be used to add nucleotides labelled with radioactive isotopes.

Also used in the immunofluorescence assay for the diagnosis of acute lymphoblastic leukemia.

It is the main enzym used in TUNEL assay (Terminal deoxynucleotidyl transferase dUTP Nick End Labeling) for the demonstration of apoptosis.