Published online 19 August 2005
Article |
A unique tRNA recognition mechanism of Caenorhabditis elegans mitochondrial EF-Tu2
1Department of Integrated Bioscience, Graduate School of Frontier Science, The University of Tokyo 5-1-5 Kashiwanoha, Kashiwa, 277-8562, Japan 2Department of Bioscience and Biotechnology, Okayama University 3-1-1 Tsushimanaka, Okayama 700-8530, Japan 3Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo 7-3-1, Hongo, Bunkyo-ku, Tokyo, Japan
*To whom correspondence should be addressed. Tel: +81 86 251 8220; Fax: +81 86 251 8219; Email: ohtsuk{at}cc.okayama-u.ac.jp
Received May 25, 2005. Revised August 4, 2005. Accepted August 4, 2005.
Nematode mitochondria expresses two types of extremely truncated tRNAs that are specifically recognized by two distinct elongation factor Tu (EF-Tu) species named EF-Tu1 and EF-Tu2. This is unlike the canonical EF-Tu molecule that participates in the standard protein biosynthesis systems, which basically recognizes all elongator tRNAs. EF-Tu2 specifically recognizes Ser-tRNASer that lacks a D arm but has a short T arm. Our previous study led us to speculate the lack of the D arm may be essential for the tRNA recognition of EF-Tu2. However, here, we showed that the EF-Tu2 can bind to D arm-bearing Ser-tRNAs, in which the DT arm interaction was weakened by the mutations. The ethylnitrosourea-modification interference assay showed that EF-Tu2 is unique, in that it interacts with the phosphate groups on the T stem on the side that is opposite to where canonical EF-Tu binds. The hydrolysis protection assay using several EF-Tu2 mutants then strongly suggests that seven C-terminal amino acid residues of EF-Tu2 are essential for its aminoacyl-tRNA-binding activity. Our results indicate that the formation of the nematode mitochondrial (mt) EF-Tu2/GTP/aminoacyl-tRNA ternary complex is probably supported by a unique interaction between the C-terminal extension of EF-Tu2 and the tRNA.
Present address: Kimitsuna Watanabe, Biological Information Research Center, National Institute of Advanced Industrial Science and Technology, 2-41-6 Aomi, Koto-ku, Tokyo 135-0064, Japan