There is strong crystallographic evidence that the 23S rRNA is the only catalytic entity in the peptidyl transferase center. Various mechanisms for the catalysis of peptidyl transfer have been proposed. Recently, attention has been given to the idea that the 23S rRNA simply acts to position the tRNA for spontaneous peptidyl transfer and that chemical catalysis may play only a secondary role. Conserved nucleotides U2585 and U2506 are thought to be involved in positioning the 3’ ends of A- and P-site substrates based on the crystallographic evidence, and because mutagenesis at these sites severely impairs peptide bond formation. In this study, pure populations of ribosomes with either U2585A or U2506G mutations in the 23S rRNA were analyzed to test the hypothesis that substitutions at nucleotides U2585 and U2506 in the peptidyl transferase center impair peptide bond formation by altering the position of the 3’ end of P-site tRNA relative to the 23S rRNA. Pure populations of mutant or wild-type ribosomes were obtained by an affinity tagging system and probed with 32P-labeled [2N3A76]tRNAPhe to determine how the 3’ end of tRNA interacts with the ribosomal proteins and 23S RNA at the peptidyl transferase center. Some of the data for the ribosomes with a G at position 2506 are consistent with a model suggested by Schmeing and coworkers in which nucleotide U2506 breaks from its original wobble base pair with nucleotide G2583 during A-site tRNA binding and swings towards the 3’ end of P-site tRNA, while nucleotide U2585 simultaneously moves away from the 3’ end of P-site tRNA.

京都大学 / 新制・課程博士 / 博士(医学) / 甲第24794号 / 医博第4986号 / 新制||医||1066(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 寺田 智祐, 教授 武藤 学, 教授 上杉 志成 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

The global market for waterborne coatings will continue to grow because alternative solventborne coatings emit environmentally hazardous volatile organic compounds (VOCs). However, most waterborne coatings are softer than solventborne crosslinked thermoset coatings because they feature thermoplastic polymer dispersions. To overcome these challenges, in this thesis we suggest a novel crosslinkable aqueous dispersion system that incorporates epoxy and amine particles into poly(methyl methacrylate) (PMMA); the particles will react when water (the solvent) evaporates, offering a potential one-component (1K) reactive system. Emulsion polymerization was used to synthesize the particles with the help of surfactants. Epoxy and amine particles were successfully incorporated during the synthesis of PMMA and formed a two-component (2K) aqueous dispersion. In this process, a non-ionic surfactant, Triton X405 (TX405), was used to prevent interactions with the amine particles. Nuclear magnetic resonance (NMR) was used to determine the actual incorporation ratios of epoxy and amine and we found an epoxy incorporation plateau. Dynamic light scattering (DLS) was used to determine the particle size distributions and a uniform distribution was observed. The pendulum test and the pencil test were used for coating hardness, which surpassed currently marketed waterborne coatings. The resulting aqueous dispersions could be cured under facile conditions, i.e., in air and at low temperatures. An increase in Tg was observed after crosslinking. Different mechanical properties were observed when the coatings were cured at different temperatures, 25°C, 70°C, and 100°C. These results suggest that we have successfully formed crosslinked coatings that contain our epoxy and amine incorporated particles, with mechanical properties comparable to the traditional solventborne coatings.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.