3'-riboguanosine (3-rG)(2'-5' linked), and the other three 3-ribonucleotide (2,5-linked) modifications are used to substitute 2-5 phosphodiester linkages for the usual 3-5 phosphodiester linkages at some or all positions of an oligonucleotide. Oligonucleotides containing all, or primarily, 2,5-phosphodiester linkages selectively bind to complementary single-stranded 3,5-RNA over comparable 3,5-DNA (1). Presumably this selectively is a consequence of the 2,5-linkages destabilizing duplexes formed with 3,5-DNA more than those formed with 3,5-RNA, leading to 25-RNA:3,5-DNA duplexes having much lower Tm than the corresponding 25-RNA:3,5-RNA duplexes. This property means that RNA oligos containing such linkages could be useful in anti-sense applications, as ssRNA-specific probes, or as ligands for affinity purification of cellular RNA.
1. Giannaris, P.A.; Damha, M.J. Oligoribonucleotides containing 2,5-phosphodiester linkages exhibit binding selectivity for 3,5-RNA over 3,5-ssDNA. Nucleic Acids Res (1993), 21: 4742-4749.