Terminal deoxynucleotidyl transferase

Terminal deoxynucleotidyl transferase (TdT), also known as DNA nucleotidylexotransferase (DNTT) or 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 V,D, and J exons during antibody gene recombination, enabling the phenomenon of junctional diversity. In humans, terminal transferase is encoded by the DNTT gene.

TdT is absent in fetal liver HSCs, significantly impairing junctional diversity in B-cells during the fetal period.

Function

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 3'-overhang, but it can also add nucleotides to blunt or recessed 3' ends. Cobalt is a necessary cofactor, however the enzyme catalyzes reaction upon Mg and Mn administration in vitro.

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

TDT

TDT may refer to:

TDT (TV station)

Tasmanian Digital Television (TDT, callsign TDT-11) is a digital television station in Tasmania, Australia. It is jointly owned by the WIN Corporation and Southern Cross Austereo, and largely managed by WIN Television.

Introduction

In Australia, the major capital cities, and a majority of the regional areas, are served by three commercial broadcasters. However, some less populated areas are only granted two licenses (and until the early 2000s, one in some cases). This is because the Australian Broadcasting Authority (ABA) believes that there is not enough advertising revenue in some areas to keep three broadcasters afloat.

In 2002, WIN Television, who had a Nine Network affiliation in Tasmania, and Southern Cross Broadcasting, who held dual Seven and Ten Network affiliations, lodged a joint application under the Broadcasting Services Act (1992) to establish a third commercial broadcaster in Tasmania. The application, by TasTV Pty Ltd (not to be confused with the former name of WIN Television in Tasmania) was successful.