Enzyme-free Regioselective Phosphorylation of Ribonucleosides is Promoted by Metal Ions

Abstract

Elucidating the pathway by which RNA efficiently emerged and persisted under prebiotic conditions remains a fundamental challenge in the origin-of-life research. The molecule capable of bridging the gap between prebiotic precursors (such as ribonucleosides and inorganic phosphate) and the spontaneous formation of an RNA chain within the thermodynamic barriers of a plausible early Earth environment still remains unclear. Here, we demonstrate that metal ions play a crucial role in promoting the regiospecific formation of 2′,3′-cyclic ribonucleotides, which are often considered as one of the competent components in RNA chain growth. By adding Ni2+ or Co2+ to a mixture of ribonucleoside, water-soluble inorganic phosphate, urea, ammonium formate and exposing it to wet-dry cycles, we observed a four-fold increase in the formation of 2′,3′-cyclic ribonucleotide compared to assay without metal ions. Dinucleotide formation was also detected in the same assay solution. The formation of the different regioisomers of mononucleotide was primarily confirmed by HPLC-based analysis, along with MALDI-ToF mass spectrometry and 31P-NMR spectroscopy. Our current finding could help in bridging the gap between how reactive RNA precursors could have formed and how those precursors eventually emerged as RNA chains needed for origin of life.