Abstract
This study evaluates the role of the N-terminal extension from yeast aspartyl-tRNA synthetase in tRNA aspartylation. The presence of an RNA-binding motif in this extension, conserved in eukaryotic class IIb aminoacyl-tRNA synthetases, provides nonspecific tRNA binding properties to this enzyme. Here, it is assumed that the additional contacts the 70 amino acid-long appendix of aspartyl-tRNA synthetase makes with tRNA could be important in expression of aspartate identity in yeast. Using in vitro transcripts mutated at identity positions, it is demonstrated that the extension grants better aminoacylation efficiency but reduced specificity to the synthetase, increasing considerably the risk of noncognate tRNA mischarging. Yeast tRNA(Glu(UUC)) and tRNA(Asn(GUU)) were identified as the most easily mischarged tRNA species. Both have a G at the discriminator position, and their anticodon differs only by one change from the GUC aspartate anticodon.
Highlights
Aminoacylation of tRNA is a key step during translation of genetic information
This study evaluates the role of the N-terminal extension from yeast aspartyl-tRNA synthetase in tRNA aspartylation
As seen in the crystal structure of yeast AspRS complexed with tRNAAsp [15], and in that recently solved of the free enzyme truncated of its first 70 amino acids [16], only the core of the enzyme is required for tRNA aspartylation
Summary
Decrease in aminoacylation specificity, thereby favoring aspartylation of noncognate tRNAs. This has functional implications for the specific expression of aspartate identity in vivo
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