Hydroxyl radical, generated by reduction of hydrogen peroxide by Fe (II)-EDTA, was used to investigate the higher-order structure of yeast tRNATyr and its chimeric mutants in aqueous solution. Exposure of free tRNATyr to this reagent gave cleavage patterns consistent with the three-dimensional structure of yeast tRNAPhe established by X-ray crystallography. This probing method was applied to detect the base-mismatches in the anticodon stem region of a chimeric tRNATyr mutant, which was constructed by ligating the 5′-half fragment of T. utilis tRNATyr and the 3′-half fragment of baker's yeast tRNATyr with T4 RNA ligase. The result of this analysis clearly showed that this probing method is sensitive enough to detect even a minute variation of the secondary structure of RNA molecules.
The coding properties of 5-methoxyuridine in the wobble position of threonine and valine tRNAs from Bacillus subtilis were investigated by the technique of aminoacyl-tRNA binding to ribosomes. 5-Methoxyuridine is recognized by A, G, and fairly well by U of the third letter of colons like uridine-5-oxyacetic acid in some tRNAs from Escherichia coli.
To study the evolution of the tRNA recognition mechanism, we constructed variants of baker's yeast tRNAThr transcripts using an in vitro transcription system and compared the recognition elements of yeast tRNAThr with those of Escherichia coli tRNAThr. In yeast tRNAThr, the second and third positions of the anticodon, G35U36, are major recognition sites, whereas the discriminator base A73 is not involved in aminoacylation. These are the same as in E. coli tRNAThr. These findings indicate the similarity of the recognition system by the cognate threonyl-tRNA synthetase functions in E. coli and yeast.
The Cu-Si alloy has been proposed as a new matrix material for filamentary Nb-Ti wires in AC use. The Cu-Si alloy shows appropriate mechanical and electrical properties. The addition of Si to the Cu matrix prevents the formation of intermetallic compounds around the Nb-Ti filaments, Ultrafine multifilamentary Nb-Ti/Cu-3.5wt%Si composite wires have been successfully fabricated. The wires show excellent performances with respect to AC loss and critical current density.
Recent studies on the fabrication of Bi (Pb)-2223 high-Tc oxides are described. Ag-sheathed tapes have been made by a powder-in-tube technique using the diffusion reaction between a high melting point and a low melting point components. Critical current density of the tape has reached 4.2×104A/cm2 at 77K and OT. The preparation of Ag-sheathed multilayered tapes are being performed through a new route.