Terminal deoxynucleotidyl transferase. catalysis of DNA (oligodeoxynucleotide) phosphorylation.

The phosphorylation and phosphonylation of the 3'-hydroxyl of oligodeoxynucleotide 3'-termini (oligodeoxynucleotidyl kinase activity) catalyzed by calf thymus terminal deoxynucleotidyl transferase (TDT) are discussed. Palpha and Palpha, Pgamma-substituted modified triphosphates serve as low-molecular weight substrates in this reaction to give oligodeoxynucleotides with a 3'-phosphorylated or phosphonylated hydroxyl. The reaction is specific for TDT, and it is not catalyzed by avian myeloblastosis virus reverse transcriptase. The phosphate or phosphonate donor activities of modified triphosphates depend on their structure and increase with hydrophobicity. Several modified triphosphates demonstrated very high substrate activity, in some cases, up to one order of magnitude higher than that for dTTP. It has also been shown that TDT catalyzes primer extension with dinucleoside 5',5'-tetraphosphates as substrates.