Transfer RNA (tRNA) – a peek into the origin of life
‘Clover structure’ of Transfer RNA
Transfer RNA (tRNA) is ancient. It is the most direct intermediary between genes and proteins. Like many other RNAs (ribonucleic acids), tRNA aids in translating genes into the chains of amino acids that make up proteins. The fact that tRNA is so central to the task of building proteins probably means that it has been around for a long time.
Professor Gustavo Caetano-Anollés and Feng-Jie Sung of Univeristy of Illinois-Urbana Champaigne had a hunch that understanding the structural properties of tRNA would shed light on how organisms and viruses evolved.
All tRNAs assemble themselves into a shape that, if flattened, resembles a cloverleaf. The team began by looking for patterns in this cloverleaf structure, using detailed data from hundreds of molecules representing virusesand each of the three superkingdoms of life: archaea (microbes that can survive in boiling acid, near sulfurous ocean vents or in other extreme environments), bacteria and eukarya.
“Perhaps in evolution there are things that are so fundamental that they are kept, held onto, for millions or even billions of years,”Caetano-Anollés said. “Those are the fossils, the molecular fossils, that tell us about the past. Therefore, studying these molecules can address fundamental questions in biology and evolution”.
They conducted the same analysis on the tRNAs of each of the superkingdoms, to see how far these groupings diverged from the overall tree. This comparison allowed them to determine the order in which viruses and each of the superkingdoms diverged.
The new analysis supports an earlier study that suggested that the archaea were the first to arise as an evolutionarily distinguishable group. The research also indicated that viruses emerged not long after the archaea, with the superkingdoms eukarya and bacteria following much later – and in that order.
This finding may influence the ongoing debate over whether viruses existed prior to, or after, the emergence of living cells, Caetano-Anollés said.
Elaine Warburton www.geneticsandhealth.com
