Nonenzymatic Template-Directed Primer Extension Using 2 '-3 ' Cyclic Nucleotides Under Wet-Dry Cycles

Abstract

RNA World Hypothesis is centred around the idea of a period in the early history of life’s origin, wherein nonenzymatic oligomerization and replication of RNA resulted in functional ribozymes. Previous studies in this endeavour have demonstrated template-directed primer extension using chemically modified nucleotides and primers. Nonetheless, similar studies that used non-activated nucleotides led to the formation of RNA only with abasic sites. In this study, we report template-directed primer extension with prebiotically relevant cyclic nucleotides, under dehydration-rehydration (DH-RH) cycles occurring at high temperature (90 °C) and alkaline conditions (pH 8). 2′–3′ cyclic nucleoside monophosphates (cNMP) resulted in primer extension, while 3′–5′ cNMP failed to do so. Intact extension of up to two nucleotide additions was observed with both canonical hydroxy-terminated (OH-primer) and activated amino-terminated (NH2-primer) primers. We demonstrate primer extension reactions using both purine and pyrimidine 2′–3′ cNMPs, with higher product yield observed during cAMP additions. Further, the presence of lipid was observed to significantly enhance the extended product in cCMP reactions. In all, our study provides a proof-of-concept for nonenzymatic primer extension of RNA, using intrinsically activated prebiotically relevant cyclic nucleotides as monomers.