NAM9 nuclear suppressor of mitochondrial ochre mutations in Saccharomyces cerevisiae codes for a protein homologous to S4 ribosomal proteins from chloroplasts, bacteria, and eucaryotes.

Boguta, Magdalena; Dmochowska, Aleksandra; Borsuk, P; Wrobel, K; Gargouri, A; Lazowska, J; Słonimski, Piotr P.; Szcześniak, Barbara; Kruszewska, A

doi:10.1128/mcb.12.1.402

Cited by 30 publications

(30 citation statements)

References 28 publications

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“…One suppressor mutation changes a single nucleotide in the highly conserved '530 loop' of 15S mitoribosomal RNA [63]. The second mutation affects the mitochondrial homolog, NAM9, of E. coli ribosomal protein $4 [62]. The effect of both nonsense suppressor mutations could be eliminated by overproduction ofmRF-1 (antisuppression [35,64]).…”

Section: Terminationmentioning

confidence: 99%

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Protein synthesis in mitochondria

Pel

Grivell

1994

Mol Biol Rep

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Section: Terminationmentioning

confidence: 99%

“…In this respect it may also be significant that mRF-1 is more similar to E. coli RF-1 than RF-2 [66]. Several mutants suppressing mitochondrial nonsense mutations have been isolated in yeast [58][59][60][61][62]. For two of these mutants, the component affected by the second-site suppressor mutation has been identified.…”

Section: Terminationmentioning

confidence: 99%

Protein synthesis in mitochondria

Pel

Grivell

1994

Mol Biol Rep

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“…One dominant suppressor, NAM9 -1 (8), and 10 recessive suppressors (9) were identified. The cloning of the NAM9 -1 gene identified a structural component of the mitochondrial ribosome homologous to the S4 ribosomal protein from bacteria and eukaryotes that controls translation fidelity (8,10). Here we show that all of the remaining recessive nuclear suppressors are mutations in a gene specifying the mitochondrial translation termination factor mRF1 (11).…”

mentioning

confidence: 99%

Mutations in the Yeast MRF1 Gene Encoding Mitochondrial Release Factor Inhibit Translation on Mitochondrial Ribosomes

Towpik

Chacińska

Cieśla

et al. 2004

Journal of Biological Chemistry

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Although the control of mitochondrial translation in the yeast Saccharomyces cerevisiae has been studied extensively, the mechanism of termination remains obscure. Ten mutations isolated in a genetic screen for read-through of premature stop codons in mitochondrial genes were localized in the chromosomal gene encoding the mitochondrial release factor mRF1. The mrf1-13 and mrf1-780 mutant genes, in contrast to other alleles, caused a non-respiratory phenotype that correlated with decreased expression of mitochondrial genes as well as a reporter ARG8 m gene inserted into mitochondrial DNA. The steady-state levels of several mitochondrially encoded proteins, but not their mRNAs, were dramatically decreased in mrf1-13 and mrf1-780 cells. Structural models of mRF1 were constructed, allowing localization of residues substituted in the mrf1 mutants and offering an insight into the possible mechanism by which these mutations change the mitochondrial translation termination fidelity. Inhibition of mitochondrial translation in mrf1-13 and mrf1-780 correlated with the three-dimensional localization of the mutated residues close to the PST motif presumably involved in the recognition of stop codons in mitochondrial mRNA.The mitochondrial genetic system of the yeast Saccharomyces cerevisiae has been a subject of intensive studies. Seven genes in the yeast mitochondrial DNA (mtDNA) 1 encode integral membrane proteins that are assembled together with subunits encoded in the nuclear DNA into multimeric respiratory complexes. Maintenance and expression of mtDNA require approximately 200 proteins encoded in the nuclear DNA and imported to mitochondria from the cytosol (1, 2). Among them are mitochondrial ribosomal proteins, general translation factors, and translational activators. Current analysis of the proteome of yeast mitochondria allowed for identification of 65 mitoribosomal proteins (2); however, only ϳ60% of these have recognizable homology with bacterial ribosomal proteins (3). Multiple mitoribosome-specific proteins in yeast and mammals demonstrate the considerable divergence of mitochondrial ribosomes from their prokaryotic ancestors (4, 5). The mechanisms that control mitochondrial translation are difficult to study because no in vitro system for the expression of translation products encoded in mtDNA has yet been established. In contrast to the biochemical difficulties, the yeast S. cerevisiae, being a facultative anaerobe, offers distinct advantages for mitochondrial genetic studies. Several hundred point mutations or small deletions called mit Ϫ have been genetically mapped and assigned to genes in mtDNA. We have long been involved in a search for suppressors of mit Ϫ mutants that act at the level of mitochondrial translation. Analogous suppressor approach applied to chromosomal mutants allowed identification of proteins responsible for translation fidelity in the yeast cytosolic system. Ribosomal proteins from the decoding center of the ribosome and translation termination factors represented two classes of prote...

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“…Wild-type Nam9p is a basic protein of 486 amino acids; in the mutant Nam9-1p, serine 82 is changed to leucine. The N-terminal domain of Nam9p reveals strong homology to the class of S4 ribosomal proteins from prokaryotes and eukaryotes (2)(3)(4). In Escherichia coli, S4 plays a key role in ribosome assembly and influences translational fidelity.…”

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confidence: 99%

Prion-Dependent Switching between Respiratory Competence and Deficiency in the Yeast nam9-1Mutant

Chacińska

Boguta

Krzewska

et al. 2000

Molecular and Cellular Biology

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Nam9p is a protein of the mitochondrial ribosome. The respiration-deficient Saccharomyces cerevisiae strain MB43-nam9-1 expresses Nam9-1p containing the point mutation S82L. Respiratory deficiency correlates with a decrease in the steady level of some mitochondrially encoded proteins and the complete lack of mitochondrially encoded cytochrome oxidase subunit 2 (Cox2). De novo synthesis of Cox2 in MB43-nam9-1 is unaffected, indicating that newly synthesized Cox2 is rapidly degraded. ] ochre mutation cox2-V25 and was subsequently shown to suppress other ochre mutations in different mitochondrial genes. Wild-type Nam9p is a basic protein of 486 amino acids; in the mutant Nam9-1p, serine 82 is changed to leucine. The N-terminal domain of Nam9p reveals strong homology to the class of S4 ribosomal proteins from prokaryotes and eukaryotes (2-4). In Escherichia coli, S4 plays a key role in ribosome assembly and influences translational fidelity. Nam9p contains an additional C-terminal domain that shows no obvious homology with any known protein. Disruption of NAM9 perturbs mitochondrial DNA integrity and causes respiratory deficiency (4). Some mutations cause temperature-dependent loss of mitochondrial 15S rRNA (2). The combined properties indicate that Nam9p is a component of the mitochondrial ribosome and that Nam9-1p acts as a nonsense suppressor, suggesting that it is involved in ensuring translational fidelity (2, 4). (For a review about mitochondrial ribosomal proteins, see reference 30.) Here we present direct evidence that both Nam9p and Nam9-1p are stably bound to the small subunit of the mitochondrial ribosome.The Saccharomyces cerevisiae strain MB43-nam9-1 expressing Nam9-1p fails to grow at 37°C and shows a delay of growth at 30°C on nonfermentable substrates. We show that the inability of the strain to respire at 30°C correlates with the lack of mitochondrially encoded cytochrome oxidase subunit 2 (Cox2) at steady-state level, whereas there is only moderate reduction of mitochondrially encoded Cox3, apocytochrome b (Cob), and Atp6, a subunit of the F 0 F 1 ATPase. Although Nam9p is involved in mitochondrial translation, the mutant Nam9-1p does not interfere with the translation of Cox2 but rather with a subsequent step, most likely related to stability or assembly. These findings place NAM9 in a group of nuclear genes that exert a posttranscriptional effect on the accumulation of specific mitochondrially encoded subunits of the cytochrome c oxidase complex (5, 31, 50, 56; for a review, see references 24 and 32).We reasoned that a screen for multicopy suppressors restoring normal respiration of the nam9-1 strain might reveal novel components of the mitochondrial translation machinery involved in either the fidelity of translation, the stability, and/or the assembly of Cox2. Unexpectedly we identified HSP104 as a strong multicopy suppressor of nam9-1. The cytosolic chaperone Hsp104 is not essential for the life of yeast but is induced during different conditions related to stress (45,46,59,63

show abstract

NAM9 nuclear suppressor of mitochondrial ochre mutations in Saccharomyces cerevisiae codes for a protein homologous to S4 ribosomal proteins from chloroplasts, bacteria, and eucaryotes.

Cited by 30 publications

References 28 publications

Protein synthesis in mitochondria

Protein synthesis in mitochondria

Mutations in the Yeast MRF1 Gene Encoding Mitochondrial Release Factor Inhibit Translation on Mitochondrial Ribosomes

Prion-Dependent Switching between Respiratory Competence and Deficiency in the Yeast nam9-1Mutant

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