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J. Biol. Chem., Vol. 279, Issue 31, 32151-32158, July 30, 2004

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Leucyl-tRNA Synthetase from the Hyperthermophilic Bacterium Aquifex aeolicus Recognizes Minihelices^*

Min-Gang Xu, Ming-Wei Zhao, and En-Duo Wang

From the State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, The Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China

Aminoacylation of the minihelix mimicking the amino acid acceptor arm of tRNA has been demonstrated in more than 10 aminoacyl-tRNA synthetase systems. Although Escherichia coli or Homo sapiens cytoplasmic leucyl-tRNA synthetase (LeuRS) is unable to charge the cognate minihelix or microhelix, we show here that minihelix^Leu is efficiently charged by Aquifex aeolicus synthetase, the only known heterodimeric LeuRS (-LeuRS). Aminoacylation of minihelices is strongly dependent on the presence of the A73 identity nucleotide and greatly stimulated by destabilization of the first base pair as reported for the E. coli isoleucyl-tRNA synthetase and methionyl-tRNA synthetase systems. In the E. coli LeuRS system, the anticodon of tRNA^Leu is not important for recognition by the synthetase. However, the addition of RNA helices that mimic the anticodon domain stimulates minihelix^Leu charging by -LeuRS, indicating possible domain-domain communication within -LeuRS. The leucine-specific domain of -LeuRS is responsible for minihelix recognition. To ensure accurate translation of the genetic code, LeuRS functions to hydrolyze misactivated amino acids (pretransfer editing) and misaminoacylated tRNA (posttransfer editing). In contrast to tRNA^Leu, minihelix^Leu is unable to induce posttransfer editing even upon the addition of the anticodon domain of tRNA. Therefore, the context of tRNA is crucial for the editing of mischarged products. However, the minihelix^Leu cannot be misaminoacylated, perhaps because of the tRNA-independent pretransfer editing activity of -LeuRS.

Received for publication, March 18, 2004 , and in revised form, May 10, 2004.

^* This work was funded by Natural Science Foundation of China Grants 30170224, 30270310, and 30330180; Chinese Academy of Sciences Grant KSCX-2-2-04; and Shanghai Committee of Science and Technology Grant 02DJ140567. 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.

To whom correspondence should be addressed. Tel.: 86-21-54921241; Fax: 86-21-54921011; E-mail: edwang{at}sibs.ac.cn.

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