Double-Stranded Polydeoxyribonucleotides Containing 6-Thiodeoxyguanosine and 6-Thiodeoxyinosine. Poly[d(A-C) . d(T-s6G)], Poly[d(A-s6G) . d(T-C)] and Poly[d(A-C) . d(T-s6I)]

Abstract

Three new double-stranded polydeoxyribonucleotides containing the nucleoside analogs 6-thiodeoxyguanosine and 6-thiodeoxyinosine were synthesized enzymatically. Poly[d(A-C) · d(T-s6G)] and poly[d(A-s6G) · d(T-C)] were prepared by extensive synthesis with DNA polymerase from Micrococcus luteus, while the same enzyme from Escherichia coli failed in extensive polymerisation but brought about the synthesis of poly[d(T-s6G)] and poly[d(T-s6I)] by the repair mechanism using single-stranded poly[d(A-C)] template and a minute amount of d(T-G)n primer. The analog-containing DNAs were characterized by ultraviolet absorption and circular dichroism spectra as well as by their stability against thermal and alkaline denaturation. The substitution by 6-thiodeoxyguanosine or 6-thiodeoxyinosine for deoxyguanosine reduces the stability of the biopolymers considerably. Exchange of the analog-containing strand by singlestranded poly[d(T-G)] takes place rapidly even at ambient temperature.