Structure of RNA and RNP

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X-ray crystallography: By crystallography of RNA-protein complexes, structural details of their interactions and roles of RNA in activities were analyzed. We determined crystal structures of aminoacyl-tRNA synthetases, which are responsible for joining corresponding tRNAs and amino acids during translation. It revealed that tRNAs play positive roles in both aminoacylation and proofreading reactions by modulating protein structures. To analyze structural bases of pre-tRNA maturation, structural studies have been done on enzymes responsible for the pre-tRNA processing and modifications. The structure of tRNA complexed with ArcTGT revealed that the modification is achieved via a step including a transitional tRNA structure "λ form". We also determined the crystal structure of Vasa, an RNA helicase involved in the differentiation of germ cells, and elucidated structural basis of the RNA double strand resolution by a DEAD-box RNA helicase.NMR: (1) Solution structures of helix 6 stem-loop RNA of SRP RNA from human and Pyrococcus furiosus were determined and the difference in recognition by SRP19 was discussed. (2) Solution structure of SmpB from Thermus thermophilus HB8 was determined and the interaction between tmRNA and SmpB was analyzed. It was found that the structure of SmpB changed upon binding of tmRNA. (3) Solution structures of stem-loop RNAs derived from UnaL2 RNA were determined. The GNRNA motif in the penta loop was found to be required for the recognition by the LINE reverse transcriptase and the flexibility of the bulged stem was found to be important for the retrotransposition initiation reaction. (4) A classification system for RNA structures, CSNA, was developed and applied for RNA structure determination by NMR.