Systematic analysis of enzymatic DNA polymerization using oligo-DNA templates and triphosphate analogs involving 2′,4′-bridged nucleosides

In order to systematically analyze the effects of nucleoside modification of sugar moieties in DNA polymerase reactions, we synthesized 16 modified templates containing 2′,4′-bridged nucleotides and three types of 2′,4′-bridged nucleoside-5′-triphospates with different bridging structures. Among the five types of thermostable DNA polymerases used, Taq, Phusion HF, Vent(exo-), KOD Dash and KOD(exo-), the KOD Dash and KOD(exo-) DNA polymerases could smoothly read through the modified templates containing 2′-O,4′-C-methylene-linked nucleotides at intervals of a few nucleotides, even at standard enzyme concentrations for 5 min. Although the Vent(exo-) DNA polymerase also read through these modified templates, kinetic study indicates that the KOD(exo-) DNA polymerase was found to be far superior to the Vent(exo-) DNA polymerase in accurate incorporation of nucleotides. When either of the DNA polymerase was used, the presence of 2′,4′-bridged nucleotides on a template strand substantially decreased the reaction rates of nucleotide incorporations. The modified templates containing sequences of seven successive 2′,4′-bridged nucleotides could not be completely transcribed by any of the DNA polymerases used; yields of longer elongated products decreased in the order of steric bulkiness of the modified sugars. Successive incorporation of 2′,4′-bridged nucleotides into extending strands using 2′,4′-bridged nucleoside-5′-triphospates was much more difficult. These data indicate that the sugar modification would have a greater effect on the polymerase reaction when it is adjacent to the elongation terminus than when it is on the template as well, as in base modification.