Bridging the prebiotic and RNA worlds: Prebiotic RNA synthesis on clay

Progress towards the laboratory demonstration of the steps in the prebiotic origin of the RNA world is reviewed. Montmorillonite clay catalyzes the fo rmation of RNAs containing 6-14 monomer units from the activated mononucleo tides of A, C, G, I and U. The RNAs formed have 3', 5'- and 2', 5'-links, p yrophosphate links and have both linear and cyclic chains. The purine oligo nucleotides have more 3', 5'- links while the pyrimidine nucleotides have m ore 2', 5'-linkages. Template-directed synthesis on the heterogeneous oligo (C)s formed on montmorillonite yields the corresponding oligo(a)s. The dime r fraction formed in the reaction of a binary mixture of a purine and pyrim idine nucleotide shows sequence selectivity with about a 20 fold excess of the 5'-purine-pyrimidine dimer over that of the 5'-pyrimidine-purine dimer. RNAs as long as 50 mers are formed by the elongation of a decamer bound to montmorillonite by the daily addition of activated monomer to it over a 14 -day time period.