The Role of Sugar-backbone Heterogeneity and Chimeras in the Simultaneous Emergence of RNA and DNA

Hypotheses of the origins of RNA and DNA are generally centered on the prebiotic synthesis of a pristine system (pre-RNA or RNA), which gives rise to its descendent. However, a lack of specificity in the synthesis of genetic polymers would likely result in chimeric sequences; the roles and fate of such sequences are unknown. Here we show that chimeras, exemplified by mixed TNA-RNA and RNA-DNA oligonucleotides, preferentially bind to, and act as templates for, homogeneous TNA-, RNA- and DNA-ligands. The chimeric-templates can act as a catalyst, mediating the ligation of oligomers to give homogenous-backbone sequences, and the regeneration of the chimeric templates potentiates a scenario for possible cross-catalytic cycle with amplification. This process provides a proof-of-principle demonstration of a heterogeneity-to-homogeneity scenario while giving credence to the idea that DNA could appear concurrently with RNA instead of being its later descendent.