Minimal requirements for molecular information transfer.

The information transfer properties of nucleic acids are largely due to the properties of the bases themselves, for which it would appear evolution has selected a highly favorable set of molecules. In aqueous solution, it is possible that this task can only be carried out efficiently by heterocyclic, condensed-ring structures fairly similar to the purines and pyrimidines. Alterations in backbone structure, however, whether in the mode of linkage or in the nature of the sugar residue, are much less critical. Such alternatives could have played a role in the emergence of life on Earth and should be considered likely in extraterrestrial environments. The possible existence of low-efficiency, information transfer systems based on other structures entirely (proteins, clay minerals, etc), remains an interesting speculation for which no evidence is presently available.