Abstract
It is still not clear how prebiotic replicators evolved towards the complexity found in present day organisms. Within the most realistic scenario for prebiotic evolution, known as the RNA world hypothesis, such complexity has arisen from replicators consisting solely of RNA. Within contemporary life, remarkably many RNAs are involved in modifying other RNAs. In hindsight, such RNA-RNA modification might have helped in alleviating the limits of complexity posed by the information threshold for RNA-only replicators. Here we study the possible role of such self-modification in early evolution, by modeling the evolution of protocells as evolving replicators, which have the opportunity to incorporate these mechanisms as a molecular tool. Evolution is studied towards a set of 25 arbitrary ‘functional’ structures, while avoiding all other (misfolded) structures, which are considered to be toxic and increase the death-rate of a protocell. The modeled protocells contain a genotype of different RNA-sequences while their phenotype is the ensemble of secondary structures they can potentially produce from these RNA-sequences. One of the secondary structures explicitly codes for a simple sequence-modification tool. This ‘RNA-adapter’ can block certain positions on other RNA-sequences through antisense base-pairing. The altered sequence can produce an alternative secondary structure, which may or may not be functional. We show that the modifying potential of interacting RNA-sequences enables these protocells to evolve high fitness under high mutation rates. Moreover, our model shows that because of toxicity of misfolded molecules, redundant coding impedes the evolution of self-modification machinery, in effect restraining the evolvability of coding structures. Hence, high mutation rates can actually promote the evolution of complex coding structures by reducing redundant coding. Protocells can successfully use RNA-adapters to modify their genotype-phenotype mapping in order to enhance the coding capacity of their genome and fit more information on smaller sized genomes.
Highlights
It has been generally accepted that replicators during the early stages of evolution, most likely formed an ‘RNA world’ [1,2], where life consisted primarily of self-replicating RNA-molecules with catalytic properties, so called ribozymes
The evolution of complexity is studied in protocells evolving towards a set of 25 pre-defined ‘functional’ secondary structures
Fitness given by a structure depends on the distance to the full secondary structure of the target
Summary
It has been generally accepted that replicators during the early stages of evolution, most likely formed an ‘RNA world’ [1,2], where life consisted primarily of self-replicating RNA-molecules with catalytic properties, so called ribozymes. RNA is considered to be extremely versatile and flexible due to the genotypephenotype mapping between genetic information and function based on the folded structure This results in properties advantageous for evolvability, such as a redundant mapping and neutrality [3,4,5], making RNA an ideal evolvable molecule [6], and : an appropriate model to study evolutionary processes in general [7,8]. Multiple proteins coded on a single gene), which is commonly used and allows for information to be stored much more economically, and a more varied proteome from a genome of limited size [13] Building on these observations, the current study will investigate the evolution of (early) replicators, when provided with the possibility to acquire a simple abstraction of a molecular tool for such self-modification of their genotypephenotype mapping
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
