[A new terminator of DNA biosynthesis--possible conformation analog of the substrate in a DNA-synthesizing complex]

2',3'-Dideoxy-2',3'-dehydrothymidine 5'-triphosphate (dddTTP) reveals the termination substrate properties in the DNA synthesis catalyzed by E. coli polymerase I (Klenow fragment), rat liver DNA polymerase beta, calf thymus terminal deoxynucleotidyl transferase, and reverse transcriptase of avian myeloblastosis virus but does not affect calf thymus DNA polymerase alpha. For DNA polymerase I, dddTTP by an order of magnitude is more effective than any known termination substrate. It is supposed that dddTTP models the conformational state of the substrate's carbohydrate moiety in the complex DNA polymerase + template-primer.