Molecular Evolution of RNA modification enzymes and RNA recognition mechanism

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In this project, we have obtained many findings in the RNA modification field.Main findings are as follows.(1) Construction of in vitro RNA modification system under high temperaturesWe have clarified roles of thermophilic-bacteria specific polyamines against the RNA modification machinery.(2) Clarifications of RNA recognition mechanisms of RNA modification enzymesWe have reported that Aquifex aeolicus TrmD [tRNA (m1 G37) methyltransferase] has a unique RNA recognition mechanism.The enzyme methylates tRNA molecules possessing not only G36G37 sequence but also A36G37 sequence. Furthermore, the enzyme methylates micro-helix RNA possessing A36G37 sequence. These results showed that A. aeolicus TrmD has a broad substarte specificity in comparison with other TrmD proteins.We have reported that eukaryote tRNA (m7G46) methyltransferase [Trm8/Trm82 complex] recognizes the D-arm structure in tRNA, demonstrating that eukaryote enzyme has a strict RNA recognition mechanism as compared to bacterial enzymes.(3) Clarifications of relationship between protein structure and RNA recognition mechanismWe performed site-directed mutagenesis study against basic amino acid residues conserved in TrmH [tRNA (Gm18) methyltransferases]. We could distinguish residues required in the first tRNA binding process and residues required in the progress of the catalytic cycles.