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Terminal Transferase (TdT)


Terminal transferase (TdT) is a template independent polymerase that catalyzes the addition of deoxynucleotides to the 3' hydroxyl terminus of DNA molecules. Protruding, recessed or blunt-ended double or single-stranded DNA molecules serve as a substrate for TdT. The 58.3 kDa enzyme does not have 5' or 3' exonuclease activity. The addition of Co2+ in the reaction makes tailing more efficient.

The enzyme is available in 500 and 2,500 unit sizes at a concentration of 20 U/µL. The enzyme is supplied with a 10× Reaction Buffer and 2.5 mM CoCl2.


  • Addition of homopolymer tails to the 3´ ends of DNA.
  • Labeling the 3´ ends of DNA with modified nucleotides (e.g., ddNTP, DIG-dUTP).
  • TUNEL asay (in situ localization of apoptosis).
  • TdT dependent PCR.

Product Specifications

  • Storage Buffer: 50 mM potassium phosphate (pH 6.4), 100 mM NaCl, 1 mM DTT, 0.1% Triton X-100, and 50% (v/v) glycerol.
  • Unit Definition: One unit is defined as the amount of enzyme catalyzing the incorporation of 1 nmol dATP into acid-insoluble material in a total reaction volume of 1 ml in 1 hour at 37°C using d(A)18 as a primer.
  • Unit Assay Conditions: 1X Reaction Buffer, 0.72 μM d(A)18, 0.2 mM dATP and 1.0 μCi [3H]- dATP in a 50 μl total reaction volume.

To Order

Buy Cat.No. Product Name Unit Price
E108-1 Terminal Transferase (TdT) 500 units $65
E108-2 Terminal Transferase (TdT) 2500 units $260


Protocol (PDF): E108