Evolutionary basis of converting a bacterial tRNA synthetase into a yeast cytoplasmic or mitochondrial enzyme.
Previous studies showed that cytoplasmic and mitochondrial forms of yeast valyl-tRNA synthetase (ValRS) are specified by the VAS1 gene through alternative initiation of translation. Sequence comparison suggests that the yeast cytoplasmic (or mature mitochondrial) ValRS contains an N-terminal appendage that acts in cis as a nonspecific tRNA-binding domain (TRBD) and is absent from its bacterial relatives. We show here that Escherichia coli ValRS can substitute for the mitochondrial and cytoplasmic functions of VAS1 by fusion of a mitochondrial targeting signal and a TRBD, respectively. In addition, the bacterial ValRS gene can be converted into a dual functional yeast gene encoding both cytoplasmic and mitochondrial activities by fusion of a DNA sequence specifying both the mitochondrial targeting signal and TRBD. In vitro assays suggested that fusion of a nonspecific TRBD to the bacterial enzyme significantly enhanced its yeast tRNA-binding and aminoacylation activities. These results not only underscore the necessity of retaining a TRBD for functioning of a tRNA synthetase in yeast cytoplasm, but also provide insights into the evolution of tRNA synthetase genes.
Chiu
Wen-Chih
WC
Department of Life Science, National Central University, Jung-li 32001, Taiwan.
Chang
Chia-Pei
CP
Wang
Chien-Chia
CC
D003593:Cytoplasm / Q000201:enzymology* / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D008928:Mitochondria / Q000201:enzymology* / Q000235:genetics; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D010442:Peptide Chain Initiation, Translational / Q000502:physiology; D021382:Protein Sorting Signals / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014637:Valine-tRNA Ligase / Q000235:genetics / Q000378:metabolism*
D029968:Escherichia coli Proteins; D024101:Mitochondrial Proteins; D021382:Protein Sorting Signals; D029701:Saccharomyces cerevisiae Proteins; D014637:Valine-tRNA Ligase