Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06517, USA.

Accurately aminoacylated tRNAs are an a priori requirement for translation of the genetic code. They are synthesized by the aminoacyl-tRNA synthetases which select both the correct amino acid and tRNA from a total of more than 400 possible combinations. Genetic, biochemical and structural studies have begun to reveal the mechanisms by which this specificity is achieved by Escherichia coli glutaminyl-tRNA synthetase (GlnRS). Sequence-specific interactions between GlnRS and tRNAGln determine both the accuracy of tRNA selection and the efficiency of aminoacylation. Thus, amino acid recognition is tRNA-dependent. Consequently, while a non-cognate tRNA may be recognized by GlnRS, the resulting tRNA:enzyme complex displanys a considerably reduced affinity for glutamine compared to wild-type. A more detailed investigation has also shown that perturbation of any of the protein-RNA interactions between GlnRS and tRNAGln results in considerable changes in glutamine affinity and suggests that the complex may function as a transient ribonucleoprotein. One major point of contact which mediates tRNA-dependent amino acid recognition in this complex appears to be between the 3'-end of the tRNA and three glutanime-contacting residues in the active site.

A comparable situation also exists in tryptophanyl-tRNA synthetase, which has been used to dissect the catalytic mechanism of tRNA-dependent amino acid recognition. Through the use of pre-steady-state kinetics, tRNA identity has been shown to significantly effect the energy required for the formation of the transition state for tRNA charging. This mechanism now provides a ready explanation as to why the majority of tRNA mischarging events, including those originally described over twenty five years ago for GlnRS, impair cellular viability only to a limited degree.

　このページの先頭

　この号の目次

　交流会・シンポジウムの記録のページ

　ホームページ