Nonenzymatic recombination of RNA by means of transesterification

High-Fidelity RNA Copying via 2',3'-Cyclic Phosphate Ligation

Templated ligation offers an efficient approach to replicate long strands in an RNA world. The 2',3'-cyclic phosphate (>P) is a prebiotically available activation that also forms during RNA hydrolysis. Using gel electrophoresis and high-performance liquid chromatography, we found that the templated ligation of RNA with >P proceeds in simple low-salt aqueous solutions with 1 mM MgCl2 under alkaline pH ranging from 9 to 11 and temperatures from -20 to 25 °C. No additional catalysts were required. In contrast to previous reports, we found an increase in the number of canonical linkages to 50%. The reaction proceeds in a sequence-specific manner, with an experimentally determined ligation fidelity of 82% at the 3' end and 91% at the 5' end of the ligation site. With splinted oligomers, five ligations created a 96-mer strand, demonstrating a pathway for the ribozyme assembly. Due to the low salt requirements, the ligation conditions will be compatible with strand separation. Templated ligation mediated by 2',3'-cyclic phosphate in alkaline conditions therefore offers a performant replication and elongation reaction for RNA on early Earth.

From formamide to RNA, the path is tenuous but continuous

Reactions of formamide (NH2COH) in the presence of catalysts of both terrestrial and meteoritic origin yield, in plausible and variegated conditions, a large panel of precursors of (pre)genetic and (pre)metabolic interest. Formamide chemistry potentially satisfies all of the steps from the very initial precursors to RNA. Water chemistry enters the scene in RNA non-enzymatic synthesis and recombination.

A model for the origin of life through rearrangements among prebiotic phosphodiester polymers

This model proposes that the origin of life on Earth occurred as a result of a process of alteration of the chemical composition of prebiotic macromolecules. The stability of organic compounds assembled into polymers generally exceeded the stability of the same compounds as free monomers. This difference in stability stimulated accumulation of prebiotic macromolecules. The prebiotic circulation of matter included constant formation and decomposition of polymers. Spontaneous chemical reactions between macromolecules with phosphodiester backbones resulted in a non-Darwinian selection for chemical stability, while formation of strong structures provided an advantage in the struggle for stability. Intermolecular structures between nucleotide-containing polymers were further stabilized by occasional acquisition of complementary nucleotides. Less stable macromolecules provided the source of nucleotides. This process resulted first in the enrichment of nucleotide content in prebiotic polymers, and subsequently in the accumulation of complementary oligonucleotides. Finally, the role of complementary copy molecules changed from the stabilization of the original templates to the de novo production of template-like molecules. I associate this stage with the origin of life in the form of cell-free molecular colonies. Original life acquired ready-to-use substrates from constantly forming prebiotic polymers. Metabolism started to develop when life began to consume more substrates than the prebiotic cycling produced. The developing utilization of non-polymeric compounds stimulated the formation of the first membrane-enveloped cells that held small soluble molecules. Cells "digested" the nucleotide-containing prebiotic macromolecules to nucleotide monomers and switched the mode of replication to the polymerization of nucleotide triphosphates.