G/C-modified oligodeoxynucleotides with selective complementarity: synthesis and hybridization properties.

Modified oligodeoxyribonucleotides (ODNs) that have unique hybridization properties were designed and synthesized for the first time. These ODNs, called selective binding complementary ODNs (SBC ODNs), are unable to form stable hybrids with each other, yet are able to form stable, sequence specific hybrids with complementary unmodified strands of nucleic acid. To make SBC ODNs, deoxyguanosine (dG) and deoxycytidine (dC) were substituted with deoxyinosine (dI) and 3-(2'-deoxy-beta-D-ribofuranosyl)pyrrolo-[2,3-d]-pyrimidine-2-(3H)-one (dP), respectively. The hybridization properties of several otherwise identical complementary ODNs containing one or both of these nucleoside analogs were studied by both UV monitored thermal denaturation and non-denaturing PAGE. The data showed that while dI and dP did form base pairs with dC and dG, respectively, dI did not form a stable base pair with dP. A self-complementary ODN uniformly substituted with dI and dP acquired single-stranded character and was able to strand invade the end of a duplex DNA better than an unsubstituted ODN. This observation implies that SBC ODNs should effectively hybridize to hairpins present in single-stranded DNA or RNA.