Origin and Evolution of RNA

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This research group tried to elucidate the mechanisms of generation and evolution of functional RNAs, and in particular those in the RNA World. For this purpose, (1) structures and functional mechanisms of the natural catalytic RNAs (ribozymes) and new functional RNAs created by the SELEX techniques were investigated, and (2) the evolutional processes of tRNAs and proteins involved in protein biosynthesis were studied at nolecular level in order to elucidate their origins.(1) The ribozyme mechanism of the M1 RNA of RNase P were elucidated by construction of a novel ribozyme that undergoes self cleavage. It was shown that the ligation reaction spontaneously occurs for RNA molecules with the terminal 2', 3'-cyclic phosphate groups. Several new functional RNAs were created by SELEX,and their roles in the RNA World were discussed.(2) The identity determinants of tRNAs from E.coli and yeast were nearly completely established, by biochemical and genetic methods. Many human genes for aminoacyl-tRNA synthetases were cloned. Thus, the origins of synthetases were classified as archaeal, eukaryotic, and bacterial. Furthermore, sme synthetase genes were indicated to have been horizontally transferred from one organism to another. Two functionally different modified nucleotides, archaeosine from archaea and queuosine from eukaryotes and eubacteria, were found unexpectedly to share the same biosynthetic mechanism of base exchange.