Codon-specific translational defect caused by a wobble modification deficiency in mutant tRNA from a human mitochondrial disease

doi:10.1073/pnas.0405173101

Codon-specific translational defect caused by a wobble modification deficiency in mutant tRNA from a human mitochondrial disease

^*Department of Chemistry and Biotechnology, Graduate School of Engineering, and ^†Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan; ^§Department of Biochemistry and Cell Biology, Institute of Development and Aging Sciences, Graduate School of Medicine, Nippon Medical School, Kanagawa 211-8533, Japan; and ^¶Department of Obstetrics and Gynecology, Nippon Medical School, Sendagi, Bunkyo-ku, Tokyo 113-8603, Japan

Edited by Dieter Söll, Yale University, New Haven, CT, and approved September 5, 2004 (received for review July 17, 2004)

Abstract

Point mutations in the mitochondrial (mt) tRNA^Leu(UUR) gene are responsible for mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), a subgroup of mitochondrial encephalomyopathic diseases. We previously showed that mt tRNA^Leu(UUR) with an A3243G or T3271C mutation derived from patients with MELAS are deficient in a normal taurine-containing modification (τm⁵U; 5-taurinomethyluridine) at the anticodon wobble position. To examine decoding disorder of the mutant tRNA due to the wobble modification deficiency independent of the pathogenic point mutation itself, we used a molecular surgery technique to construct an mt tRNA^Leu(UUR) molecule lacking the taurine modification but without the pathogenic mutation. This “operated” mt tRNA^Leu(UUR) without the taurine modification showed severely reduced UUG translation but no decrease in UUA translation. We thus concluded that the UUG codon–specific translational defect of the mutant mt tRNAs^Leu(UUR) is the primary cause of MELAS at the molecular level. This result could explain the complex I deficiency observed clinically in MELAS.

Footnotes

↵ ** To whom correspondence should be addressed. E-mail: ts{at}chembio.t.u-tokyo.ac.jp.
↵ ‡ Present address: Medical Research Council, Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, United Kingdom.
↵ ∥ Present address: Biological Information Research Center, National Institute of Advanced Industrial Science and Technology, 2-41-6 Aomi, Koto-ku, Tokyo 135-0064, Japan.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: MELAS, mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes; MERRF, myoclonus epilepsy associated with ragged red fibers; np, nucleotide position; mt, mitochondrial; τm⁵U 5-taurinomethyluridine; τm⁵s²U, 5-taurinomethyl-2-thiouridine.