Nucleic acid-like structures. II. Polynucleotide analogues as possible primitive precursors of nucleic acids.

Activated derivatives of purine-containing deoxynucleoside- diphosphates spontaneously oligomerize to produce pyrophosphate- linked oligodeoxynucleotide analogues. These analogues are of potential interest as models of primitive, polynucleotide precursors. The efficiency of oligomerization (ImpdGpIm and ImpdApIm much greater than ImpdIpIm) appears to reflect a combination of stacking forces and the specific geometric orientations of the stacked units. Under favorable conditions, chain lengths greater than 20 have been obtained for oligomers containing pdGp in the absence of a template. In the presence of a complementary template, the activated derivatives of pdGp and pdAp oligomerize much more extensively. An acyclo-analogue of G has also been shown to undergo template-directed oligomerization on pol (C). These observations suggest the possibility that primitive information transfer might have evolved in much simpler systems and that this function was taken over by polynucleotides at a later stage in evolution.