Terminal Deoxyribonucleotidyl Transferase (EC 2.7.7.31)

Terminal deoxyribonucleotidyl transferase (TdT) (EC 2.7.7.3 1) catalyzes the addition of deoxynucleoside triphosphates to the 3′ ends of oligo-and polynucleotide primers. Different from all the other known DNA polymerases, TdT-catalyzed DNA synthesis is not template-directed. The reaction can be described as:

Only one dNTP is necessary for polymerization, although any dNTP (and derivatives thereof) or any combination of dNTPs will serve as substrate.