Terminal Transferase from calf thymus

Bovine terminal transferase (TdT) is a primer-dependent polymerase that catalyzes the addition of deoxynucleotides to the 3′-OH terminus of DNA molecules with the release of inorganic phosphate. TdT reacts preferentially with either single-stranded DNA molecules or double-stranded-DNA with 3′ overhangs, but procedures have been developed to label blunt ends or 3′-recessive ends. In a reaction mixture, the divalent ion (Co²⁺, Mn²⁺, Mg²⁺) will influence purine and pyrimidine polymerization rate. Activities of TdT are also affected by the bases (dATP, dCTP, dGTP and dTTP) present.

Suitable for:

• Addition of homopolymers to vectors, inserts and cDNA for cloning
• Labeling the 3′-end of double- and single-stranded DNA with non-radioactive or radioactive labels
• Carrying out in vitro mutagenesis by adding single nucleotides to DNA
• Use in TUNEL assays

Terminal transferase is supplied as a solution of 50 mM potassium phosphate (pH 7.4), 1 mM 2-mercaptoethanol and 50% glycerol (v/v).

One unit will incorporate 1 nanomole of dATP into acid-precipitable material in one hour at 37 °C using d(pT)₆ as primer.

Activity assay uses 200 mM potassium cacodylate, pH 7.2, 4 mM MgCl₂, 1 mM 2-mercaptoethanol, 1 mM ³H-dATP, 70 μM d(pT)₆, 37 °C.