Terminal Deoxynucleotidyl Transferase
Encyclopedia
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-nucleotide
s to the V,D, and J
exon
s during antibody gene recombination enabling the phenomenon of junctional diversity
. In humans, terminal transferase is encoded by the DNTT gene
.
TdT is notably absent in fetal liver HSCs significantly impairing junctional diversity
in B-cells during the fetal period.
the addition of nucleotide
s 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.
. 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 labeled with radioactive isotope
s, 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
.
DNA polymerase
A DNA polymerase is an enzyme that helps catalyze in the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best known for their feedback role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....
expressed in immature, pre-B, pre-T lymphoid
Lymphoid
Lymphoid is a term used to describe lymph or the lymphatic system.In the context of lymphoid leukemia, it refers specifically to lymphocytes Lymphoid leukemias and lymphomas are now considered to be tumors of the same type of cell lineage. They are called "leukemia" when in the blood or marrow and...
cells, and acute lymphoblastic leukemia
Acute lymphoblastic leukemia
Acute lymphoblastic leukemia is a form of leukemia, or cancer of the white blood cells characterized by excess lymphoblasts.Malignant, immature white blood cells continuously multiply and are overproduced in the bone marrow. ALL causes damage and death by crowding out normal cells in the bone...
/lymphoma cells. TdT adds N-nucleotide
N-nucleotide
N-nucleotides, or nontemplated nucleotides are believed to exist only to create diversity at VJ junctions during lymphocyte development . The addition of these nucleotides is aided by an enzyme called Terminal deoxynucleotidyl transferase...
s to the V,D, and J
V(D)J recombination
VJ recombination, also known as somatic recombination, is a mechanism of genetic recombination in the early stages of immunoglobulin and T cell receptors production of the immune system...
exon
Exon
An exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule either after portions of a precursor RNA have been removed by cis-splicing or when two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA...
s during antibody gene recombination enabling the phenomenon of junctional diversity
Junctional diversity
Junctional diversity describes the DNA sequence variations introduced by the improper joining of gene segments during the process of VJ recombination...
. In humans, terminal transferase is encoded by the DNTT gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
.
TdT is notably absent in fetal liver HSCs significantly impairing junctional diversity
Junctional diversity
Junctional diversity describes the DNA sequence variations introduced by the improper joining of gene segments during the process of VJ recombination...
in B-cells during the fetal period.
Function
TdT catalysesCatalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
the addition of nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
s to the 3' terminus
DNA end
DNA end or sticky end refers to the properties of the end of a molecule of DNA or a recombinant DNA molecule. The concept is important in molecular biology, especially in cloning or when subcloning inserts DNA into vector DNA. All the terms can also be used in reference to RNA. The sticky ends or...
of a DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
molecule. Unlike most DNA polymerases it does not require a template. The preferred substrate of this enzyme is a 3'-overhang
DNA end
DNA end or sticky end refers to the properties of the end of a molecule of DNA or a recombinant DNA molecule. The concept is important in molecular biology, especially in cloning or when subcloning inserts DNA into vector DNA. All the terms can also be used in reference to RNA. The sticky ends or...
, but it can also add nucleotides to blunt or recessed 3' ends. Cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
is a necessary cofactor
Cofactor (biochemistry)
A cofactor is a non-protein chemical compound that is bound to a protein and is required for the protein's biological activity. These proteins are commonly enzymes, and cofactors can be considered "helper molecules" that assist in biochemical transformations....
, however the enzyme catalyzes reaction upon Mg and Mn administration in vitro.
Uses
Terminal transferase has applications in molecular biologyMolecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
. 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 labeled with radioactive isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
s, for example in the TUNEL assay
TUNEL assay
Terminal deoxynucleotidyl transferase dUTP nick end labeling is a method for detecting DNA fragmentation by labeling the terminal end of nucleic acids.- Method :...
(Terminal deoxynucleotidyl transferase dUTP Nick End Labeling) for the demonstration of apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
(which is marked, in part, by fragmented DNA).
Also used in the immunofluorescence assay for the diagnosis of acute lymphoblastic leukemia
Acute lymphoblastic leukemia
Acute lymphoblastic leukemia is a form of leukemia, or cancer of the white blood cells characterized by excess lymphoblasts.Malignant, immature white blood cells continuously multiply and are overproduced in the bone marrow. ALL causes damage and death by crowding out normal cells in the bone...
.