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Title: Yeast mitochondrial threonyl-tRNA synthetase recognizes tRNA isoacceptors by distinct mechanisms and promotes CUN codon reassignment

Aminoacyl-tRNA synthetases (aaRSs) ensure faithful translation of mRNA into protein by coupling an amino acid to a set of tRNAs with conserved anticodon sequences. Here, we show that in mitochondria of Saccharomyces cerevisiae, a single aaRS (MST1) recognizes and aminoacylates two natural tRNAs that contain anticodon loops of different size and sequence. Besides a regular ?? with a threonine (Thr) anticodon, MST1 also recognizes an unusual ??, which contains an enlarged anticodon loop and an anticodon triplet that reassigns the CUN codons from leucine to threonine. Our data show that MST1 recognizes the anticodon loop in both tRNAs, but employs distinct recognition mechanisms. The size but not the sequence of the anticodon loop is critical for ?? recognition, whereas the anticodon sequence is essential for aminoacylation of ??. The crystal structure of MST1 reveals that, while lacking the N-terminal editing domain, the enzyme closely resembles the bacterial threonyl-tRNA synthetase (ThrRS). A detailed structural comparison with Escherichia coli ThrRS, which is unable to aminoacylate ??, reveals differences in the anticodon-binding domain that probably allow recognition of the distinct anticodon loops. Finally, our mutational and modeling analyses identify the structural elements in MST1 (e.g., helix {alpha}11) that define tRNA selectivity. Thus, MTS1more » exemplifies that a single aaRS can recognize completely divergent anticodon loops of natural isoacceptor tRNAs and that in doing so it facilitates the reassignment of the genetic code in yeast mitochondria.« less
Authors:
; ; ; ; ;  [1] ;  [2]
  1. (Yale)
  2. (
Publication Date:
OSTI Identifier:
1036321
Resource Type:
Journal Article
Resource Relation:
Journal Name: Proc. Natl. Acad. Sci. USA; Journal Volume: 109; Journal Issue: (9) ; 02, 2012
Research Org:
Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
Sponsoring Org:
OTHERNIGMS
Country of Publication:
United States
Language:
ENGLISH
Subject:
59 BASIC BIOLOGICAL SCIENCES; 60 APPLIED LIFE SCIENCES; AMINO ACIDS; CODONS; CRYSTAL STRUCTURE; ENZYMES; ESCHERICHIA COLI; GENETICS; LEUCINE; LIGASES; MITOCHONDRIA; PROTEINS; SACCHAROMYCES CEREVISIAE; SIMULATION; SYNTHESIS; THREONINE; TRIPLETS; YEASTS