Phenylalanyl-tRNA synthetase editing defects result in efficient mistranslation of phenylalanine codons as tyrosine
Abstract
Translational quality control is monitored at several steps, including substrate selection by aminoacyl-tRNA synthetases (aaRSs), and discrimination of aminoacyl-tRNAs by elongation factor Tu (EF-Tu) and the ribosome. Phenylalanyl-tRNA synthetase (PheRS) misactivates Tyr but is able to correct the mistake using a proofreading activity named editing. Previously we found that overproduction of editing-defective PheRS resulted in Tyr incorporation at Phe-encoded positions in vivo, although the misreading efficiency could not be estimated. This raised the question as to whether or not EF-Tu and the ribosome provide further proofreading mechanisms to prevent mistranslation of Phe codons by Tyr. Here we show that, after evading editing by PheRS, Tyr-tRNAPhe is recognized by EF-Tu as efficiently as the cognate Phe-tRNAPhe. Kinetic decoding studies using full-length Tyr-tRNAPhe and Phe-tRNAPhe, as well as a poly(U)-directed polyTyr/polyPhe synthesis assay, indicate that the ribosome lacks discrimination between Tyr-tRNAPhe and Phe-tRNAPhe. Taken together, these data suggest that PheRS editing is the major proofreading step that prevents infiltration of Tyr into Phe codons during translation.
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Footnotes
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Reprint requests to: Michael Ibba, Department of Microbiology, The Ohio State University, 484 West 12th Avenue, Columbus, OH 43210-1292, USA; e-mail: ibba.1{at}osu.edu; fax: 614-292-8120.
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Article published online ahead of print. Article and publication date are at http://www.rnajournal.org/cgi/doi/10.1261/rna.684107.
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- Received June 18, 2007.
- Accepted July 25, 2007.
- Copyright © 2007 RNA Society
