RESUMO
The mitochondrial oxidative phosphorylation system comprises complexes assembled from subunits derived from mitochondrial and nuclear gene expression. Both genetic systems are coordinated by feedback loops, which control the synthesis of specific mitochondrial encoded subunits. Here, we studied how this occurs in the case of cytochrome b, a key subunit of mitochondrial complex III. Our data suggest the presence of a molecular rheostat consisting of two translational activators, Cbp3-Cbp6 and Cbs1, which operates at the mitoribosomal tunnel exit to connect translational output with assembly efficiency. When Cbp3-Cbp6 is engaged in assembly of cytochrome b, Cbs1 binds to the tunnel exit to sequester the cytochrome b-encoding mRNA, repressing its translation. After mediating complex III assembly, binding of Cbp3-Cbp6 to the tunnel exit replaces Cbs1 and the bound mRNA to permit cytochrome b synthesis. Collectively, the data indicate the molecular wiring of a feedback loop to regulate synthesis of a mitochondrial encoded protein.
Assuntos
Regulação da Expressão Gênica , Mitocôndrias/genética , Proteínas Mitocondriais/metabolismo , Biossíntese de Proteínas , Proteínas de Saccharomyces cerevisiae/metabolismo , Citocromos b/biossíntese , Citocromos b/genética , Proteínas de Membrana/metabolismo , Mitocôndrias/metabolismo , Proteínas Mitocondriais/genética , Chaperonas Moleculares/metabolismo , RNA Mensageiro/análise , Proteínas de Ligação a RNA/genética , Proteínas de Ligação a RNA/metabolismo , Ribossomos/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Transativadores/metabolismoRESUMO
Mitochondrial gene expression in Saccharomyces cerevisiae is responsible for the production of highly hydrophobic subunits of the oxidative phosphorylation system. Membrane insertion occurs cotranslationally on membrane-bound mitochondrial ribosomes. Here, by employing a systematic mass spectrometry-based approach, we discovered the previously uncharacterized membrane protein Mrx15 that interacts via a soluble C-terminal domain with the large ribosomal subunit. Mrx15 contacts mitochondrial translation products during their synthesis and plays, together with the ribosome receptor Mba1, an overlapping role in cotranslational protein insertion. Taken together, our data reveal how these ribosome receptors organize membrane protein biogenesis in mitochondria.
Assuntos
Proteínas de Membrana/metabolismo , Mitocôndrias/metabolismo , Proteínas Mitocondriais/metabolismo , Biossíntese de Proteínas , Receptores Citoplasmáticos e Nucleares/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/metabolismo , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Epistasia Genética , Deleção de Genes , Espectrometria de Massas , Membranas Mitocondriais/metabolismo , Peptídeos/metabolismo , Ligação Proteica , Subunidades Ribossômicas/metabolismo , Saccharomyces cerevisiae/genéticaAssuntos
Proteínas Fúngicas/biossíntese , Mitocôndrias/metabolismo , Proteínas Mitocondriais/biossíntese , Ribossomos Mitocondriais/metabolismo , Complexos Multiproteicos/biossíntese , Leveduras/metabolismo , DNA Fúngico/genética , DNA Fúngico/metabolismo , DNA Mitocondrial/genética , DNA Mitocondrial/metabolismo , Proteínas Fúngicas/genética , Regulação Fúngica da Expressão Gênica , Mitocôndrias/genética , Proteínas Mitocondriais/genética , Complexos Multiproteicos/genética , Processamento Pós-Transcricional do RNA , RNA Fúngico/genética , RNA Fúngico/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Transcrição Gênica , Leveduras/genéticaRESUMO
Mitochondria contain their own genetic system that provides subunits of the complexes driving oxidative phosphorylation. A quarter of the mitochondrial proteome participates in gene expression, but how all these factors are orchestrated and spatially organized is currently unknown. Here, we established a method to purify and analyze native and intact complexes of mitochondrial ribosomes. Quantitative mass spectrometry revealed extensive interactions of ribosomes with factors involved in all the steps of posttranscriptional gene expression. These interactions result in large expressosome-like assemblies that we termed mitochondrial organization of gene expression (MIOREX) complexes. Superresolution microscopy revealed that most MIOREX complexes are evenly distributed throughout the mitochondrial network, whereas a subset is present as nucleoid-MIOREX complexes that unite the whole spectrum of organellar gene expression. Our work therefore provides a conceptual framework for the spatial organization of mitochondrial protein synthesis that likely developed to facilitate gene expression in the organelle.
