title: Evolutionary and genetic analyses of mitochondrial translation initiation factors identify the missing mitochondrial IF3 in S. cerevisiae.
abstract: Mitochondrial translation is essentially bacteria-like, reflecting the bacterial endosymbiotic ancestry of the eukaryotic organelle. However, unlike the translation system of its bacterial ancestors, mitochondrial translation is limited to just a few mRNAs, mainly coding for components of the respiratory complex. The classical bacterial initiation factors (IFs) IF1, IF2 and IF3 are universal in bacteria, but only IF2 is universal in mitochondria (mIF2). We analyse the distribution of mitochondrial translation initiation factors and their sequence features, given two well-propagated claims: first, a sequence insertion in mitochondrial IF2 (mIF2) compensates for the universal lack of IF1 in mitochondria, and secondly, no homologue of mitochondrial IF3 (mIF3) is identifiable in Saccharomyces cerevisiae. Our comparative sequence analysis shows that, in fact, the mIF2 insertion is highly variable and restricted in length and primary sequence conservation to vertebrates, while phylogenetic and in vivo complementation analyses reveal that an uncharacterized S. cerevisiae mitochondrial protein currently named Aim23p is a bona fide evolutionary and functional orthologue of mIF3. Our results highlight the lineage-specific nature of mitochondrial translation and emphasise that comparative analyses among diverse taxa are essential for understanding whether generalizations from model organisms can be made across eukaryotes.
authors.affiliation: University of Tartu, Institute of Technology, Tartu, Estonia. gemma.atkinson@ut.ee
authors.forename: Gemma C
authors.initials: GC
authors.lastname: Atkinson
authors.forename: Anton
authors.initials: A
authors.lastname: Kuzmenko
authors.forename: Piotr
authors.initials: P
authors.lastname: Kamenski
authors.forename: Mikhail Y
authors.initials: MY
authors.lastname: Vysokikh
authors.forename: Valentina
authors.initials: V
authors.lastname: Lakunina
authors.forename: Stoyan
authors.initials: S
authors.lastname: Tankov
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Smirnova
authors.forename: Aksel
authors.initials: A
authors.lastname: Soosaar
authors.forename: Tanel
authors.initials: T
authors.lastname: Tenson
authors.forename: Vasili
authors.initials: V
authors.lastname: Hauryliuk
mesh_terms: D000595:Amino Acid Sequence; D017124:Conserved Sequence; D015852:Eukaryotic Initiation Factor-2 / Q000737:chemistry / Q000145:classification / Q000235:genetics; D039621:Eukaryotic Initiation Factor-3 / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D005816:Genetic Complementation Test; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D016415:Sequence Alignment
chemical_list: D015852:Eukaryotic Initiation Factor-2; D039621:Eukaryotic Initiation Factor-3; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins