Probable presence of an ubiquitous cryptic mitochondrial gene on the antisense strand of the cytochrome oxidase I gene
1 LATP, CNRS-UMR 6632, IFR 48 Infectiopôle, Evolution biologique et modélisation, case 5, Université de Provence, Place Victor Hugo, 13331 Marseille cedex 3, France
2 Departamento de Ingeniería Genética, CINVESTAV, Irapuato Km 9.6 Libramiento Norte Carr. Irapuato-León 36821 Irapuato Gto, México
3 Biovays SAS, Université de Provence, 3, place Victor Hugo, 13331 Marseille cedex 3, France
4 INRA, UMR1163 de Biotechnologie des Champignons Filamenteux, IFR86-BAIM. Aix-Marseille Universités, ESIL, 163 avenue de Luminy, CP 925, 13288 Marseille Cedex 09, France
5 Aix-Marseille Univ, UMR1163 BCF, 163 avenue de Luminy, CP925, 13288 Marseille Cedex 09, France
6 National Collections of Natural History, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel
7 Department of Life Sciences, Ben Gurion University, 84105 Beer Sheva, Israel
Biology Direct 2011, 6:56 doi:10.1186/1745-6150-6-56Published: 24 October 2011
Mitochondria mediate most of the energy production that occurs in the majority of eukaryotic organisms. These subcellular organelles contain a genome that differs from the nuclear genome and is referred to as mitochondrial DNA (mtDNA). Despite a disparity in gene content, all mtDNAs encode at least two components of the mitochondrial electron transport chain, including cytochrome c oxidase I (Cox1).
Presentation of the hypothesis
A positionally conserved ORF has been found on the complementary strand of the cox1 genes of both eukaryotic mitochondria (protist, plant, fungal and animal) and alpha-proteobacteria. This putative gene has been named gau for gene antisense ubiquitous in mtDNAs. The length of the deduced protein is approximately 100 amino acids. In vertebrates, several stop codons have been found in the mt gau region, and potentially functional gau regions have been found in nuclear genomes. However, a recent bioinformatics study showed that several hypothetical overlapping mt genes could be predicted, including gau; this involves the possible import of the cytosolic AGR tRNA into the mitochondria and/or the expression of mt antisense tRNAs with anticodons recognizing AGR codons according to an alternative genetic code that is induced by the presence of suppressor tRNAs. Despite an evolutionary distance of at least 1.5 to 2.0 billion years, the deduced Gau proteins share some conserved amino acid signatures and structure, which suggests a possible conserved function. Moreover, BLAST analysis identified rare, sense-oriented ESTs with poly(A) tails that include the entire gau region. Immunohistochemical analyses using an anti-Gau monoclonal antibody revealed strict co-localization of Gau proteins and a mitochondrial marker.
Testing the hypothesis
This hypothesis could be tested by purifying the gau gene product and determining its sequence. Cell biological experiments are needed to determine the physiological role of this protein.
Implications of the hypothesis
Studies of the gau ORF will shed light on the origin of novel genes and their functions in organelles and could also have medical implications for human diseases that are caused by mitochondrial dysfunction. Moreover, this strengthens evidence for mitochondrial genes coded according to an overlapping genetic code.