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TerminalDeoxynucleotidylTransferase(TdT)catalyzestheincorporationofsingledeoxynucleotidesintothe3"-OHterminusofsingle-ordouble-strandedDNA,makingitaneffectiveagentin3"endlabelingapplicationssuchasTerminaldUTPnickendlabeling(TUNEL).TerminalDeoxynucleotidylTransferase(TdT)requiresanoligodeoxynucleotideofatleastthreebasesasaprimer,butisnottemplate-dependent.