Self-condensation of activated dinucleotides on polynucleotide templates with alternating sequences.

We have prepared substantial quantities of the alternating polymers poly(U-G) and poly(C-A) and have used them as templates for the self-condensation of ImpApC, ImpCpA, ImpGpU and ImpG. We find that the condensation of ImpGpU and ImpUpG on poly(C-A) is efficient, the condensation of ImpCpA on poly(U-G) is moderately efficient, while the condensation of ImpApC on poly(U-C) proceeds poorly. In many cases, the product is predominantly 3'-5'-linked. These reactions demonstrate unequivocally, for the first time, that template-directed reactions occur in double-helical structures. Furthermore, they describe for the first time a pair of reactions in which each of two complementary polymers facilitates the synthesis of the other. The prebiotic significance of these findings is discussed.