Terminal deoxynucleotidyl transferase enzyme: Homopolymers

Terminal deoxynucleotidyl transferase (TdT), catalyzes the incorporations of nucleotides at the end of 3’OH of single strand / double strand DNA without using template.
The calf thymus glands are an abundant source for TdT and immature B and T cells do contain TDT
TdT is truly a monomeric protein with a mw of 58,000 to 60,000 kDa
TDT consist of two to three splice variants in murine, human and bovine etc
One of the variant has 3 ‘ to 5’ exonuclease activity
TdT plays a crucial role in the evolution and adaptation of the vertebrate immune system
For polymerization of nucleotides, it requires initiator complex at least three nucleotides long with 5’ free phosphate and 3’OH for extension.
TDT requires divalent cataions for catalysis but it can use four different ion Mg2+,Mn2+ Zn2+ and Co2+.
It has been used in synthesis of second strand cDNA
To label the primer 3’ end with highly radio active nucleotides
And used in the preparation of biotinylated or fluoresceinated probes for blotting techniques
TDT used in tunnel assay for detection of apoptotic cells

[@vijjumahankali4297]

Tdt does not require template strand so it is called template independent polymerase ... sir does this involve in exonuclease activity

[@Dr.DNA-Primer]

One of the variant of Mammalian TDT have 3'to 5' exonuclease activity