RNA evolution conjectured from tRNA and riboswitches

The structures of tRNAs and riboswitches comprise distinct domains. A tRNA molecule is L-shaped, and each arm may reflect its evolution. The amino acid-nonspecific minihelix domain may have emerged before the amino acid- specific anticodon-containing domain was acquired. The glycine riboswitch of Bacillus subtilis functions in a "glycine- independent" manner in the presence of polyethylene glycol or ethylene glycol. The effect is dependent only on the existence of a terminator stem within the expression platform of the riboswitch and is indepen- dent of the aptamer domain. Similar to the hypothesis that explains the evolution of tRNA function, the specificity of riboswitch functional domains may have increased during evolution. Collectively, these views provide new perspectives on the evolution of RNA.