Ironing Out the RNA World

Friday September 28 at 3.15 p.m.
Högbomsalen, level 3, Geovetenskapens hus
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by Professor Loren Williams

School of Chemistry and Biochemistry
Georgia Tech, Atlanta, Georgia 


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Ironing Out the RNA World

In RNA World models of the origin of life, RNA was the primary biopolymer of early genetics and catalysis. RNA-based life inhabited an ancient earth described by geologists as rich in soluble iron and lacking in free oxygen. Anoxia persisted for around a billion years before photosynthesis began producing substantial free oxygen. We believe that the catalytic competence of ancient RNAs may have been greater on the early earth than in extant conditions. The ‘great oxidation’ led to depletion of soluble iron from the biosphere. We hypothesize that RNA used Fe2+ as a cofactor when iron was benign and abundant, and experienced metal substitution during the great oxidation, whereby Mg2+ replaced Fe2+. Our hypothesis is supported by our experimental observations that (i) RNA folding is conserved between complexes with Fe2+ and Mg2+ and (ii) at least some ribozymes are more active in the presence of Fe2+ than Mg2+. We observe that reversing the putative RNA substitution, by removing Mg2+ and adding back Fe2+, in an anoxic environment, expands the catalytic repertoire of RNA. Fe2+ confers on RNA a previously uncharacterized ability, to catalyze electron transfer. Catalysis is specific, in that it is dependent on the type of RNA. The 23S rRNA, one of the most ancient RNAs in biology, is found to be the most efficient electron transfer ribozyme among the RNAs studied.

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