Human Molecular Genetics Advance Access originally published online on July 25, 2007
Human Molecular Genetics 2007 16(20):2472-2481; doi:10.1093/hmg/ddm203
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The A3243G tRNALeu(UUR) mutation induces mitochondrial dysfunction and variable disease expression without dominant negative acting translational defects in complex IV subunits at UUR codons
1 Department of Molecular Cell Biology and 2 Biomolecular Mass Spectrometry Unit, Department of Parasitology, Leiden University Medical Centre, Post Zone S1-P, Einthovenweg 20, PO Box 9600, 2300RC Leiden, The Netherlands
* To whom correspondence should be addressed. Tel: +31 71 526 9263; Fax: +31 71 526 8270; E-mail: G.M.C.Janssen{at}lumc.nl
Received April 26, 2007; Revised June 1, 2007; Accepted July 22, 2007
Mutations in the mitochondrial tRNALeu(UUR) gene are associated with a large variety of human diseases through a largely undisclosed mechanism. The A3243G tRNALeu(UUR) mutation leads to reduction of mitochondrial DNA (mtDNA)-encoded proteins and oxidative phosphorylation activity even when the cells are competent in mitochondrial translation. These two aspects led to the suggestion that a dominant negative factor may underlie the diversity of disease expression. Here we test the hypothesis that A3243G tRNALeu(UUR) generates such a dominant negative gain-of-function defect through misincorporation of amino acids at UUR codons of mtDNA-encoded proteins. Using an anti-complex IV immunocapture technique and mass spectrometry, we show that the mtDNA-encoded cytochrome c oxidase I (COX I) and COX II exist exclusively with the correct amino acid sequences in A3243G cells in a misassembled complex IV. A dominant negative component therefore cannot account for disease phenotype, leaving tissue-specific accumulation by mtDNA segregation as the most likely cause of variable mitochondrial disease expression.
This paper is dedicated to the memory of the late Professor Wim Möller (1930–2005), a remarkable man, molecular biologist at Leiden University and pioneer of ribosome structure and function.
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors.