Natural Homolog of tRNA Synthetase Editing Domain Rescues Conditional Lethality Caused by Mistranslation

• Published in: The Journal of biological chemistry Vol. 283; no. 44; pp. 30073 - 30078
• Main Authors: Chong, Yeeting E., Yang, Xiang-Lei, Schimmel, Paul
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 31.10.2008; American Society for Biochemistry and Molecular Biology
• Subjects: Alanine - chemistry; Amino Acid Sequence; Amino Acyl-tRNA Synthetases - metabolism; Aminoacylation; Catalysis; Genetic Complementation Test; Lysine - chemistry; Models, Biological; Molecular Basis of Cell and Developmental Biology; Molecular Sequence Data; Protein Biosynthesis; Protein Structure, Tertiary; RNA, Transfer - metabolism; Sequence Homology, Amino Acid; Serine - chemistry; Transgenes
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M805943200

AlaXp is a widely distributed (from bacteria to humans) genome-encoded homolog of the editing domain of alanyl-tRNA synthetases. Editing repairs the confusion of serine and glycine for alanine through clearance of mischarged (with Ser or Gly) tRNAAla. Because genome-encoded fragments of editing domains of other synthetases are scarce, the AlaXp redundancy of the editing domain of alanyl-tRNA synthetase is thought to reflect an unusual sensitivity of cells to mistranslation at codons for Ala. Indeed, a small defect in the editing activity of alanyl-tRNA synthetase is causally linked to neurodegeneration in the mouse. Although limited earlier studies demonstrated that AlaXp deacylated mischarged tRNAAlain vitro, the significance of this activity in vivo has not been clear. Here we describe a bacterial system specifically designed to investigate activity of AlaXp in vivo. Serine toxicity, experienced by a strain harboring an editing-defective alanyl-tRNA synthetase, was rescued by an AlaXp-encoding transgene. Rescue was dependent on amino acid residues in AlaXp that are needed for its in vitro catalytic activity. Thus, the editing activity per se of AlaXp was essential for suppressing mistranslation. The results support the idea that the unique widespread distribution of AlaXp arises from the singular difficulties, for translation, poised by alanine.