We report on the formation of novel RNA molecules in a recombination-like, nonenzymatic reaction proceeding in the complex of partially complementary RNA-oligonucleotides under very simple conditions. Analysis of the isolated products demonstrated that at least 5% of the formed linkages are of the (natural) 3',5'-phosphodiester type. We suggest that similar reactions could contribute to the development of the 'RNA world', but could also proceed in vivo within variously structured RNA or RNA complexes containing loops, bulges, or dangling ends, providing an emergence of novel RNA sequences.

Abstract. The nonenzymatic template-directed ligation of oligonucleotides containing 2 ,3 -cyclic phosphate was investigated in the presence of divalent cations. Ligation of the oligonucleotides readily occurred in the presence of Mg 2+ , Mn 2+ , Co 2+ , Zn 2+ , Pb 2+ . Efficacy of the metal ion catalysts inversely correlated with pKa values of the metal-bound water molecules. The intermolecular transesterification reaction yielded at least 95% of 2 ,5 -phosphodiester bonds independently on the nature of the metal ion. Relatively high reaction yields (up to 15%) suggest, that RNA fragmentation to oligonucleotides with 2 ,3 -cyclic phosphates, followed by reactions of those oligonucleotides could provide a source of new RNA molecules under prebiotic conditions.