Further, Polymerase λ has also been found to exhibit similar template-independent synthetic activity. Along with activity as a terminal transferase, it is known to also work in a more general template-dependent fashion. The similarities between TdT and polymerase μ suggest they are closely evolutionarily related. Uses Terminal transferase has applications in molecular biology. It can be used in RACE to add nucleotides that can then be used as a template for a primer in subsequent PCR. It can also be used to add nucleotides labeled with radioactive isotopes, for example in the TUNEL assay (Terminal deoxynucleotidyl transferase dUTP Nick End Labeling) for the demonstration of apoptosis (which is marked, in part, by fragmented DNA). It is also used in the immunofluorescence assay for the diagnosis of acute lymphoblastic leukemia. In immunohistochemistry and flow cytometry, antibodies to TdT can be used to demonstrate the presence of immature T and B cells and pluripotent hematopoietic stem cells, which possess the antigen, while mature lymphoid cells are always TdT-negative. While TdT-positive cells are found in small numbers in healthy lymph nodes and tonsils, the malignant cells of acute lymphoblastic leukemia are also TdT-positive, and the antibody can, therefore, be used as part of a panel to diagnose this disease and to distinguish it from, for example, small cell tumors of childhood. TdT has also seen recent application in the De Novo synthesis of oligonucleotides, with TdT-dNTP tethered analogs capable of primer extension by 1 nt at a time. In other words, the enzyme TdT has demonstrated the capability of making synthetic DNA by adding one letter at a time to a primer sequence. See also DNA DNA polymerase References Further reading External links EC 2.7.7