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.http://www.creative-enzymes.com/product/Native-Calf-Terminal-Transferase_1462.html