title: Significance of stereochemistry of 3'-terminal phosphorothioate-modified primer in DNA polymerase-mediated chain extension.
abstract: Influence of stereochemistry of the 3'-terminal phosphorothioate (PS)-modified primers was studied in a single base extension (SBE) assay to evaluate any improvements in specificity. SBE reactions were catalyzed by members of the high fidelity Pfu family of DNA polymerases with (exo+) or without (exo-) 3' --> 5' exonucleolytic activity. The diastereomerically pure PS-labeled primers used in these studies were obtained either by the stereospecific chemical synthesis invented in our laboratory or by the more conventional ion-exchange chromatographic method for separation of a mixture of diastereomers (R(P) and S(P)). When the SBE reaction was performed in the presence of mispaired 2'-deoxyribonucleoside triphosphates (dNTPs), the "racemic" 3'-phosphorothioate primer mixture resulted in a lower level of 3' --> 5' exonuclease-mediated cleavage products in comparison to the SBE reactions carried out with the corresponding unmodified primer. When the diastereomerically pure RP 3'-phosphorothioate primer was examined, the results were largely the same as for the racemic 3'-phosphorothioate primer mixture. In contrast, a 3'-PS primer of S(P) configuration displayed significantly improved performance in the SBE reaction. This included the lack of 3' --> 5' proofreading products, less mispriming, and improved yield of incorporation of the correct nucleotide.
authors.affiliation: Department of Bioorganic Chemistry, Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Lodz, Poland. bnawrot@bio.cbmm.lodz.pl
authors.forename: Barbara
authors.initials: B
authors.lastname: Nawrot
authors.forename: Natasha
authors.initials: N
authors.lastname: Paul
authors.forename: Beata
authors.initials: B
authors.lastname: Rebowska
authors.forename: Wojciech J
authors.initials: WJ
authors.lastname: Stec