A system of two polymerases--a model for the origin of life.
What was the first living molecule--RNA or protein? This question embodies the major disagreement in studies on the origin of life. The fact that in contemporary cells RNA polymerase is a protein and peptidyl transferase consists of RNA suggests the existence of a mutual catalytic dependence between these two kinds of biopolymers. I suggest that this dependence is a 'frozen accident', a remnant from the first living system. This system is proposed to be a combination of an RNA molecule capable of catalyzing amino acid polymerization and the resulting protein functioning as an RNA-dependent RNA polymerase. The specificity of the protein synthesis is thought to be achieved by the composition of the surrounding medium and the specificity of the RNA synthesis--by Watson-Crick base pairing. Despite its apparent simplicity, the system possesses a great potential to evolve into a primitive ribosome and further to life, as it is seen today. This model provides a possible explanation for the origin of the interaction between nucleic acids and protein. Based on the suggested system, I propose a new definition of life as a system of nucleic acid and protein polymerases with a constant supply of monomers, energy and protection.
Kunin
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Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel.
D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D019143:Evolution, Molecular; D008957:Models, Genetic; D000069497:Origin of Life; D011506:Proteins / Q000235:genetics*; D012313:RNA / Q000235:genetics*; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism
D011506:Proteins; D012313:RNA; D012324:RNA-Dependent RNA Polymerase; D012321:DNA-Directed RNA Polymerases