(2′-5′)-Oligo-3′-Deoxynucleotides: Selective Binding to Single-Stranded RNA but Not DNA

Oligodeoxynucleotides with (2'-5') internucleotide linkages have been synthesized on a solid support via standard cyanoethyl phosphoramidite chemistry. This simple change in the oligonucleotide bond connectivity led to unique properties. UV melting temperature experiments indicate that the (2'-5')-oligo-3'-deoxyadenylates, (2'-5')-3'-dA8 and (2'-5')-3'-dA8(s) phosphorothioate, hybridize selectively to single-stranded RNA but not DNA. The complex (2'-5')-3'-dA8:poly (U) (Tm = 32 degrees C) was nearly as stable as the natural (3'-5')-2'-dA8 and poly (U) (Tm = 33 degrees C) in 130 mM NaCl, and 10 mM phosphate buffer (pH 7.5). However, no association was observed upon mixing (2'-5')-3'-dA8 and poly (dT). The (2'-5') linkages also confer greater resistance to exo- and endonucleolytic degradation compared with (3'-5')-linked oligomers. The rate of degradation of (2'-5')-3'-dA8 was almost four times less than that of (3'-5')-2'-dA8 in cell culture medium containing 10% heat-inactivated fetal calf serum. An increase in stability for (2'-5')-3'-dA8 against endonuclease activity was observed in both cytoplasmic and nuclear extracts. The nucleic acid selectivity of (2'-5')-oligo-3'-deoxynucleotides may represent an important design feature to improve the efficacy of antisense oligonucleotides.