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posted 03. November 2006 16:47
Evolution Based on Design-by-Contract: Origin of Life through an abiotic double-stranded RNA world
by Albert D.G. de Roos
Abstract: It is generally believed that life first evolved from ssRNA (ssRNA) that both stored genetic information and catalyzed the reactions required for self-replication. By modeling early genome evolution on the engineering paradigm design-by-contract, an alternative scenario is presented in which life started with the appearance of double-stranded RNA (dsRNA) as an informational storage molecule while catalytic single-stranded RNA was derived from this dsRNA template later in evolution. Double-stranded RNA can be formed abiotically by hybridization of oligoribonucleotides that are subsequently non-enzymatically ligated into a double-stranded chain. Thermal cycling driven by the diurnal temperature cycles can replicate this dsRNA when strands of dsRNA separate and later rehybridize with oligonucleotides that are subsequently ligated to reform dsRNA. Temperature-dependent partial replication of specific regions of dsRNA can produce the first template-based generation of catalytic ssRNA, similar to the developmental gene transcription process. Thus, the dsRNA-first scenario can be implemented by gradual processes based on abiotic ligation of oligonucleotides and hybridization of complementary nucleotides. Further transition from a dsRNA to a dsDNA world can be based on minor mutations in template and substrate recognition sites of an existing RNA polymerase. Therefore, by defining evolution as an expanding system of functionalities in which existing interfaces remain intact, the ‘dsRNA first’ hypothesis provides a relatively simple gradual evolutionary scenario for the origin of Life.
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