3 '-modified oligo(2 '-O-methylribonucleotides) as improved probes for hybridization with RNA

A series Of octa(2'-O-methylribonucleotides) with an additional 3'-terminal deoxynucleoside (T W, dA or dG) linked by the 3'-3' (inverted) bond was synthesized. The exceptional stability of these oligomers to a 3'-exonuclease (SVP) and nucleases in culture medium containing 10% heat-inactivated fetal calf serum was demonstrated. It was shown that the addition of the 3'-dangling inverted deoxynucleoside increases substantially the thermal stability of the duplexes of oligo(2'-O-methylribonucleotides) with complementary RNA and DNA in the case Of a relatively weak terminal A(m)U(T) pair and enhances the mismatch sensitivity.