3'-rG (2'-5' linked)

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 2’5’-RNA:3’,5’-DNA duplexes having much lower Tm than the corresponding 2’5’-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.