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J. Biol. Chem., Vol. 281, Issue 44, 33217-33225, November 3, 2006

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A Viable Amino Acid Editing Activity in the Leucyl-tRNA Synthetase CP1-splicing Domain Is Not Required in the Yeast Mitochondria^*

From the Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-3732

Aminoacyl-tRNA synthetases are a family of enzymes that are responsible for translating the genetic code in the first step of protein synthesis. Some aminoacyl-tRNA synthetases have editing activities to clear their mistakes and enhance fidelity. Leucyl-tRNA synthetases have a hydrolytic active site that resides in a discrete amino acid editing domain called CP1. Mutational analysis within yeast mitochondrial leucyl-tRNA synthetase showed that the enzyme has maintained an editing active site that is competent for post-transfer editing of mischarged tRNA similar to other leucyl-tRNA synthetases. These mutations that altered or abolished leucyl-tRNA synthetase editing were introduced into complementation assays. Cell viability and mitochondrial function were largely unaffected in the presence of high levels of non-leucine amino acids. In contrast, these editing-defective mutations limited cell viability in Escherichia coli. It is possible that the yeast mitochondria have evolved to tolerate lower levels of fidelity in protein synthesis or have developed alternate mechanisms to enhance discrimination of leucine from non-cognate amino acids that can be misactivated by leucyl-tRNA synthetase.

Received for publication, August 3, 2006 , and in revised form, September 5, 2006.

^* This work was supported in part by National Institutes of Health Grants GM63107 and GM63789 and the Robert A. Welch Foundation (E-1404). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. of Biochemistry, University of Illinois at Urbana-Champaign, 419 Roger Adams Laboratory, Box B-4, 600 S. Mathews Ave., Urbana, IL 61801-3732. Tel.: 217-244-2405; Fax: 217-244-5858; E-mail: martinis{at}life.uiuc.edu.

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