title: Promoting the formation of an active synthetase/tRNA complex by a nonspecific tRNA-binding domain.
abstract: Previous studies showed that valyl-tRNA synthetase of Saccharomyces cerevisiae contains an N-terminal polypeptide extension of 97 residues, which is absent from its bacterial relatives, but is conserved in its mammalian homologues. We showed herein that this appended domain and its human counterpart are both nonspecific tRNA-binding domains (K(d) approximately 0.5 microm). Deletion of the appended domain from the yeast enzyme severely impaired its tRNA binding, aminoacylation, and complementation activities. This N-domain-deleted yeast valyl-tRNA synthetase mutant could be rescued by fusion of the equivalent domain from its human homologue. Moreover, fusion of the N-domain of the yeast enzyme or its human counterpart to Escherichia coli glutaminyl-tRNA synthetase enabled the otherwise "inactive" prokaryotic enzyme to function as a yeast enzyme in vivo. Different from the native yeast enzyme, which showed different affinities toward mixed tRNA populations, the fusion enzyme exhibited similar binding affinities for all yeast tRNAs. These results not only underscore the significance of nonspecific tRNA binding in aminoacylation, but also provide insights into the mechanism of the formation of aminoacyl-tRNAs.
authors.affiliation: Department of Life Science, National Central University, Jung-li, 32001 Taiwan.
authors.forename: Chia-Pei
authors.initials: CP
authors.lastname: Chang
authors.forename: Grace
authors.initials: G
authors.lastname: Lin
authors.forename: Shun-Jia
authors.initials: SJ
authors.lastname: Chen
authors.forename: Wen-Chih
authors.initials: WC
authors.lastname: Chiu
authors.forename: Wen-Heng
authors.initials: WH
authors.lastname: Chen
authors.forename: Chien-Chia
authors.initials: CC
authors.lastname: Wang