Rolling-circle and strand-displacement mechanisms for non-enzymatic RNA replication at the time of the origin of life

• Main Authors: Higgs, P.G (Author), Tupper, A.S (Author)
• Format: Article
• Language: English
• Published: Academic Press 2021
• Subjects: catalysis; displacement; DNA replication; DNA Replication; enzyme activity; evolution; genetic recombination; Non-enzymatic template-directed replication; origin of life; Origin of Life; polymerase chain reaction; Recombination, Genetic; RNA; RNA viruses; RNA World; Rolling circle; Strand-displacement; Viroids
• Online Access: View Fulltext in Publisher

 It is likely that RNA replication began non-enzymatically, and that polymerases were later selected to speed up the process. We consider replication mechanisms in modern viruses and ask which of these is possible non-enzymatically, using mathematical models and experimental data found in the literature to estimate rates of RNA synthesis and replication. Replication via alternating plus and minus strands is found in some single-stranded RNA viruses. However, if this occurred non-enzymatically it would lead to double-stranded RNA that would not separate. With some form of environmental cycling, such as temperature, salinity, or pH cycling, double-stranded RNA can be melted to form single-stranded RNA, although re-annealing of existing strands would then occur much faster than synthesis of new strands. We show that re-annealing blocks this form of replication at a very low concentration of strands. Other kinds of viruses synthesize linear double strands from single strands and then make new single strands from double strands via strand-displacement. This does not require environmental cycling and is not blocked by re-annealing. However, under non-enzymatic conditions, if strand-displacement occurs from a linear template, we expect the incomplete new strand to be almost always displaced by the tail end of the old strand through toehold-mediated displacement. A third kind of replication in viruses and viroids is rolling-circle replication which occurs via strand-displacement on a circular template. Rolling-circle replication does not require environmental cycling and is not prevented by toehold-mediated displacement. Rolling-circle replication is therefore expected to occur non-enzymatically and is a likely starting point for the evolution of polymerase-catalysed replication. © 2021 The Author(s)