OLIGORIBONUCLEOTIDES CONTAINING 2',5'-PHOSPHODIESTER LINKAGES EXHIBIT BINDING SELECTIVITY FOR 3',5'-RNA OVER 3',5'-SSDNA

Oligoribonucleotides containing 2',5'-phosphodiester linkages have been synthesized on a solid support by the 'silyl-phosphoramidite' method. The stability of complexes formed between these oligonucleotides and complementary 3',5'-RNA strands have been studied using oligoadenylates and a variety of oligonucleotides of mixed base sequences including phosphorothioate backbones. In many cases, particularly for 2',5'-linked adenylates, the UV melting profiles are quite sharp and exhibit large hyperchromic changes. Substituting a few 3',5'-linkages with the 2',5'-linkage within an oligomer lowers the T(m) of the complex and the degree of destabilization depends on the neighboring residues and neighboring linkages. The 2',5'-linked oligoribonucleotides prepared in this study exhibited remarkable selectivity for complementary single stranded RNA over DNA. For example, in 0.01 M phosphate buffer - 0.10 M NaCl (pH 7.0), no association was observed between 2',5'-r(CCC UCU CCC UUC U) and its Watson - Crick DNA complement 3',5'-d(AGAAGGGAGAGGG). However. 2',5'-r(CCC UCU CCC UUC U) with its RNA complement 3',5'-r(AGAAGGGAGAGGG) forms a duplex which melts at 40-degrees-C. The decamer 2',5'-r(Ap)9A forms a complex with both poly dT and poly rU but the complex [2',5'-r(Ap)9A ]: [poly dT] is unstable (T(m), - 1-degrees-C) and is seen only at high salt concentrations. In view of their unnatural character and remarkable selectivity for single stranded RNA, 2',5'-oligo-RNAs and their derivatives may find use as selective inhibitors of viral mRNA translation. and as affinity ligands for the purification of cellular RNA.