Heteropolynucleotides as templates for non-enzymatic polymerizations.

We have studied a number of condensation reactions involving ImpU, ImpT, ImpC, ImpA, ImpG, ImpUgG and ImpCpA as activated nucleotide donors and a variety of homo- and hetero-polynucleotides as templates. We did not not obtain any evidence of a template effect with ImpU and ImpT, but observed some condensation of ImpC with GpG on appropriate templates. ImpA and ImpG take part in a number of more or less efficient template-directed reactions, as do ImpUpG and ImpCpA. Our results suggest that, on the primitive Earth, pyrimidine nucleotides could most easily have been incorporated into polymers as constituents of short oligomers, which contained one or more purine nucleotide. The linkage of the product depends strongly on the nature of the substrates; the percentage of the natural 3'-5'-linkage was, in some cases, less than 10% and, in others, as high as 70%. Wobble-pairing was often very effective in promoting condensations, suggesting that transition mutations would have been very frequent in prebiotic polynucleotide replication.