Terminal Transferase and Leukemia

Terminal deoxynucleotidyl transferase (TdT) is an enzyme that catalyzes the elongation of preformed oligomeric or polymeric DNA chains by adding deoxyribonucleoside monophosphates to the 3′-OH ends of these chains.1 It was discovered independently by Bollum and his colleagues2 , 3 and by Krakow et al.4 Two features of TdT make it a unique and interesting enzyme. The first is that, unlike any other DNA-synthesizing enzyme (DNA polymerase), it does not use nucleic acid templates for instruction. Consequently, it has no apparent biologic role in DNA replication or repair. Secondly, in a survey of many tissues, Chang showed that appreciable levels of TdT . . .