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Mechanisms and regulation of protein synthesis in mitochondria. Nat Rev Mol Cell Biol 2021; 22:307-325. [PMID: 33594280 DOI: 10.1038/s41580-021-00332-2] [Citation(s) in RCA: 159] [Impact Index Per Article: 53.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/13/2021] [Indexed: 02/06/2023]
Abstract
Mitochondria are cellular organelles responsible for generation of chemical energy in the process called oxidative phosphorylation. They originate from a bacterial ancestor and maintain their own genome, which is expressed by designated, mitochondrial transcription and translation machineries that differ from those operating for nuclear gene expression. In particular, the mitochondrial protein synthesis machinery is structurally and functionally very different from that governing eukaryotic, cytosolic translation. Despite harbouring their own genetic information, mitochondria are far from being independent of the rest of the cell and, conversely, cellular fitness is closely linked to mitochondrial function. Mitochondria depend heavily on the import of nuclear-encoded proteins for gene expression and function, and hence engage in extensive inter-compartmental crosstalk to regulate their proteome. This connectivity allows mitochondria to adapt to changes in cellular conditions and also mediates responses to stress and mitochondrial dysfunction. With a focus on mammals and yeast, we review fundamental insights that have been made into the biogenesis, architecture and mechanisms of the mitochondrial translation apparatus in the past years owing to the emergence of numerous near-atomic structures and a considerable amount of biochemical work. Moreover, we discuss how cellular mitochondrial protein expression is regulated, including aspects of mRNA and tRNA maturation and stability, roles of auxiliary factors, such as translation regulators, that adapt mitochondrial translation rates, and the importance of inter-compartmental crosstalk with nuclear gene expression and cytosolic translation and how it enables integration of mitochondrial translation into the cellular context.
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Abstract
Mitochondria are essential organelles in eukaryotes. Most mitochondrial proteins are encoded by the nuclear genome and translated in the cytosol. Nuclear-encoded mitochondrial proteins need to be imported, processed, folded, and assembled into their functional states. To maintain protein homeostasis (proteostasis), mitochondria are equipped with a distinct set of quality control machineries. Deficiencies in such systems lead to mitochondrial dysfunction, which is a hallmark of aging and many human diseases, such as neurodegenerative diseases, cardiovascular diseases, and cancer. In this review, we discuss the unique challenges and solutions of proteostasis in mitochondria. The import machinery coordinates with mitochondrial proteases and chaperones to maintain the mitochondrial proteome. Moreover, mitochondrial proteostasis depends on cytosolic protein quality control mechanisms during crises. In turn, mitochondria facilitate cytosolic proteostasis. Increasing evidence suggests that enhancing mitochondrial proteostasis may hold therapeutic potential to protect against protein aggregation-associated cellular defects.
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Affiliation(s)
- Linhao Ruan
- Center for Cell Dynamics, Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA; , , , , ,
- Biochemistry, Cellular and Molecular Biology (BCMB) Graduate Program, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA
- Department of Chemical and Biomolecular Engineering, Whiting School of Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Yuhao Wang
- Center for Cell Dynamics, Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA; , , , , ,
- Biochemistry, Cellular and Molecular Biology (BCMB) Graduate Program, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA
- Department of Chemical and Biomolecular Engineering, Whiting School of Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Xi Zhang
- Center for Cell Dynamics, Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA; , , , , ,
- Department of Chemical and Biomolecular Engineering, Whiting School of Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Alexis Tomaszewski
- Center for Cell Dynamics, Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA; , , , , ,
- Biochemistry, Cellular and Molecular Biology (BCMB) Graduate Program, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA
- Department of Chemical and Biomolecular Engineering, Whiting School of Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Joshua T McNamara
- Center for Cell Dynamics, Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA; , , , , ,
- Biochemistry, Cellular and Molecular Biology (BCMB) Graduate Program, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA
- Department of Chemical and Biomolecular Engineering, Whiting School of Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Rong Li
- Center for Cell Dynamics, Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA; , , , , ,
- Department of Chemical and Biomolecular Engineering, Whiting School of Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
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3
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In Saccharomyces cerevisiae, withdrawal of the carbon source results in detachment of glycolytic enzymes from the cytoskeleton and in actin reorganization. Fungal Biol 2020; 124:15-23. [DOI: 10.1016/j.funbio.2019.10.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Revised: 09/20/2019] [Accepted: 10/09/2019] [Indexed: 11/19/2022]
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4
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Barros MH, McStay GP. Modular biogenesis of mitochondrial respiratory complexes. Mitochondrion 2019; 50:94-114. [PMID: 31669617 DOI: 10.1016/j.mito.2019.10.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 09/04/2019] [Accepted: 10/10/2019] [Indexed: 11/29/2022]
Abstract
Mitochondrial function relies on the activity of oxidative phosphorylation to synthesise ATP and generate an electrochemical gradient across the inner mitochondrial membrane. These coupled processes are mediated by five multi-subunit complexes that reside in this inner membrane. These complexes are the product of both nuclear and mitochondrial gene products. Defects in the function or assembly of these complexes can lead to mitochondrial diseases due to deficits in energy production and mitochondrial functions. Appropriate biogenesis and function are mediated by a complex number of assembly factors that promote maturation of specific complex subunits to form the active oxidative phosphorylation complex. The understanding of the biogenesis of each complex has been informed by studies in both simple eukaryotes such as Saccharomyces cerevisiae and human patients with mitochondrial diseases. These studies reveal each complex assembles through a pathway using specific subunits and assembly factors to form kinetically distinct but related assembly modules. The current understanding of these complexes has embraced the revolutions in genomics and proteomics to further our knowledge on the impact of mitochondrial biology in genetics, medicine, and evolution.
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Affiliation(s)
- Mario H Barros
- Departamento de Microbiologia - Instituto de Ciências Biomédicas, Universidade de São Paulo, Brazil.
| | - Gavin P McStay
- Department of Biological Sciences, Staffordshire University, Stoke-on-Trent, United Kingdom.
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Derbikova KS, Levitsky SA, Chicherin IV, Vinogradova EN, Kamenski PA. Activation of Yeast Mitochondrial Translation: Who Is in Charge? BIOCHEMISTRY (MOSCOW) 2018; 83:87-97. [DOI: 10.1134/s0006297918020013] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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6
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García-Guerrero AE, Camacho-Villasana Y, Zamudio-Ochoa A, Winge DR, Pérez-Martínez X. Cbp3 and Cbp6 are dispensable for synthesis regulation of cytochrome b in yeast mitochondria. J Biol Chem 2018; 293:5585-5599. [PMID: 29475949 DOI: 10.1074/jbc.ra117.000547] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Revised: 02/08/2018] [Indexed: 11/06/2022] Open
Abstract
Cytochrome b (Cytb) is the only mitochondrial encoded subunit from the bc1 complex. Cbp3 and Cbp6 are chaperones necessary for translation of the COB mRNA and Cytb hemylation. Here we demonstrate that their role in translation is dispensable in some laboratory strains, whereas their role in Cytb hemylation seems to be universally conserved. BY4742 yeast requires Cbp3 and Cbp6 for efficient COB mRNA translation, whereas the D273-10b strain synthesizes Cytb at wildtype levels in the absence of Cbp3 and Cbp6. Steady-state levels of Cytb are close to wildtype in mutant D273-10b cells, and Cytb forms non-functional, supercomplex-like species with cytochrome c oxidase, in which at least core 1, cytochrome c1, and Rieske iron-sulfur subunits are present. We demonstrated that Cbp3 interacts with the mitochondrial ribosome and with the COB mRNA in both BY4742 and D273-10b strains. The polymorphism(s) causing the differential function of Cbp3, Cbp6, and the assembly feedback regulation of Cytb synthesis is of nuclear origin rather than mitochondrial, and Smt1, a COB mRNA-binding protein, does not seem to be involved in the observed differential phenotype. Our results indicate that the essential role of Cbp3 and Cbp6 is to assist Cytb hemylation and demonstrate that in the absence of heme b, Cytb can form non-functional supercomplexes with cytochrome c oxidase. Our observations support that an additional protein or proteins are involved in Cytb synthesis in some yeast strains.
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Affiliation(s)
- Aldo E García-Guerrero
- From the Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Circuito Exterior s/n Ciudad Universitaria, Coyoacán, 04510 Mexico City, Mexico and
| | - Yolanda Camacho-Villasana
- From the Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Circuito Exterior s/n Ciudad Universitaria, Coyoacán, 04510 Mexico City, Mexico and
| | - Angélica Zamudio-Ochoa
- From the Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Circuito Exterior s/n Ciudad Universitaria, Coyoacán, 04510 Mexico City, Mexico and
| | - Dennis R Winge
- the Department of Medicine and Biochemistry, University of Utah Health Sciences Center, Salt Lake, Utah 84132
| | - Xochitl Pérez-Martínez
- From the Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Circuito Exterior s/n Ciudad Universitaria, Coyoacán, 04510 Mexico City, Mexico and
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Wang Y, Yan J, Zhang Q, Ma X, Zhang J, Su M, Wang X, Huang Y. The Schizosaccharomyces pombe PPR protein Ppr10 associates with a novel protein Mpa1 and acts as a mitochondrial translational activator. Nucleic Acids Res 2017; 45:3323-3340. [PMID: 28334955 PMCID: PMC5389468 DOI: 10.1093/nar/gkx127] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Accepted: 02/14/2017] [Indexed: 01/15/2023] Open
Abstract
The pentatricopeptide repeat (PPR) proteins characterized by tandem repeats of a degenerate 35-amino-acid motif function in all aspects of organellar RNA metabolism, many of which are essential for organellar gene expression. In this study, we report the characterization of a fission yeast Schizosaccharomyces pombe PPR protein, Ppr10 and a novel Ppr10-associated protein, designated Mpa1. The ppr10 deletion mutant exhibits growth defects in respiratory media, and is dramatically impaired for viability during the late-stationary phase. Deletion of ppr10 affects the accumulation of specific mitochondrial mRNAs. Furthermore, deletion of ppr10 severely impairs mitochondrial protein synthesis, suggesting that Ppr10 plays a general role in mitochondrial protein synthesis. Ppr10 interacts with Mpa1 in vivo and in vitro and the two proteins colocalize in the mitochondrial matrix. The ppr10 and mpa1 deletion mutants exhibit very similar phenotypes. One of Mpa1's functions is to maintain the normal protein level of Ppr10 protein by protecting it from degradation by the mitochondrial matrix protease Lon1. Our findings suggest that Ppr10 functions as a general mitochondrial translational activator, likely through interaction with mitochondrial mRNAs and mitochondrial translation initiation factor Mti2, and that Ppr10 requires Mpa1 association for stability and function.
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Affiliation(s)
- Yirong Wang
- Jiangsu Key Laboratory for Microbes and Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, China
| | - Jianhua Yan
- Jiangsu Key Laboratory for Microbes and Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, China
| | - Qingzhen Zhang
- Jiangsu Key Laboratory for Microbes and Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, China
| | - Xuting Ma
- Jiangsu Key Laboratory for Microbes and Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, China
| | - Juan Zhang
- Jiangsu Key Laboratory for Microbes and Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, China
| | - Minghui Su
- Jiangsu Key Laboratory for Microbes and Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, China
| | - Xiaojun Wang
- Jiangsu Key Laboratory for Microbes and Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, China
| | - Ying Huang
- Jiangsu Key Laboratory for Microbes and Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, China
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Su CH, Tzagoloff A. Cox16 protein is physically associated with Cox1p assembly intermediates and with cytochrome oxidase. J Biol Chem 2017; 292:16277-16283. [PMID: 28821616 DOI: 10.1074/jbc.m117.801811] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2017] [Revised: 08/16/2017] [Indexed: 11/06/2022] Open
Abstract
Mitochondrial cytochrome oxidase (COX) catalyzes the last step in the respiratory pathway. In the yeast Saccharomyces cerevisiae, this inner membrane complex is composed of 11 protein subunits. Expression of COX is assisted by some two dozen ancillary proteins that intercede at different stages of the assembly pathway. One such protein, Cox16p, encoded by COX16, was shown to be essential for the activity and assembly of COX. The function of Cox16p, however, has not been determined. We present evidence that Cox16p is present in Cox1p assembly intermediates and in COX. This is based on the finding that Cox16p, tagged with a dual polyhistidine and protein C tag, co-immunopurified with Cox1p assembly intermediates. The pulldown assays also indicated the presence of Cox16p in mature COX and in supercomplexes consisting of COX and the bc1 complex. From the Western signal strengths, Cox16p appears to be substoichiometric with Cox1p and Cox4p, which could indicate that Cox16p is only present in a fraction of COX. In conclusion, our results indicate that Cox16p is a constituent of several Cox1p assembly intermediates and of COX.
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Affiliation(s)
- Chen-Hsien Su
- From the Department of Biological Sciences, Columbia University, New York, New York 10027
| | - Alexander Tzagoloff
- From the Department of Biological Sciences, Columbia University, New York, New York 10027
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Vázquez-Acevedo M, Rubalcava-Gracia D, González-Halphen D. In vitro import and assembly of the nucleus-encoded mitochondrial subunit III of cytochrome c oxidase (Cox3). Mitochondrion 2014; 19 Pt B:314-22. [PMID: 24561572 DOI: 10.1016/j.mito.2014.02.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Revised: 01/24/2014] [Accepted: 02/12/2014] [Indexed: 11/17/2022]
Abstract
The cox3 gene, encoding subunit III of cytochrome c oxidase (Cox3) is in mitochondrial genomes except in chlorophycean algae, where it is localized in the nucleus. Therefore, algae like Chlamydomonas reinhardtii, Polytomella sp. and Volvox carteri, synthesize the Cox3 polypeptide in the cytosol, import it into mitochondria, and integrate it into the cytochrome c oxidase complex. In this work, we followed the in vitro internalization of the Cox3 precursor by isolated, import-competent mitochondria of Polytomella sp. In this colorless alga, the precursor Cox3 protein is synthesized with a long, cleavable, N-terminal mitochondrial targeting sequence (MTS) of 98 residues. In an import time course, a transient Cox3 intermediate was identified, suggesting that the long MTS is processed more than once. The first processing step is sensitive to the metalo-protease inhibitor 1,10-ortophenantroline, suggesting that it is probably carried out by the matrix-located Mitochondrial Processing Protease. Cox3 is readily imported through an energy-dependent import pathway and integrated into the inner mitochondrial membrane, becoming resistant to carbonate extraction. Furthermore, the imported Cox3 protein was assembled into cytochrome c oxidase, as judged by the presence of a labeled band co-migrating with complex IV in Blue Native Electrophoresis. A model for the biogenesis of Cox3 in chlorophycean algae is proposed. This is the first time that the in vitro mitochondrial import of a cytosol-synthesized Cox3 subunit is described.
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Affiliation(s)
- Miriam Vázquez-Acevedo
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-243, México 04510, D.F., Mexico
| | - Diana Rubalcava-Gracia
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-243, México 04510, D.F., Mexico
| | - Diego González-Halphen
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-243, México 04510, D.F., Mexico.
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10
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Kuzmenko A, Atkinson GC, Levitskii S, Zenkin N, Tenson T, Hauryliuk V, Kamenski P. Mitochondrial translation initiation machinery: conservation and diversification. Biochimie 2013; 100:132-40. [PMID: 23954798 PMCID: PMC3978653 DOI: 10.1016/j.biochi.2013.07.024] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2013] [Accepted: 07/29/2013] [Indexed: 11/29/2022]
Abstract
The highly streamlined mitochondrial genome encodes almost exclusively a handful of transmembrane components of the respiratory chain complex. In order to ensure the correct assembly of the respiratory chain, the products of these genes must be produced in the correct stoichiometry and inserted into the membrane, posing a unique challenge to the mitochondrial translational system. In this review we describe the proteins orchestrating mitochondrial translation initiation: bacterial-like general initiation factors mIF2 and mIF3, as well as mitochondria-specific components – mRNA-specific translational activators and mRNA-nonspecific accessory initiation factors. We consider how the fast rate of evolution in these organelles has not only created a system that is divergent from that of its bacterial ancestors, but has led to a huge diversity in lineage specific mechanistic features of mitochondrial translation initiation among eukaryotes. Mitochondrially-encoded proteins are mostly respiratory chain components. The mitochondrial translation system is thus organized in a very specific way. Initiation involves mRNA-specific activators and bacteria-like initiation factors. We show that Saccharomyces cerevisiae Aim23p is a functional ortholog of bacterial IF3. We review the lineage specific features of mitochondrial translation initiation.
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Affiliation(s)
- Anton Kuzmenko
- University of Tartu, Institute of Technology, Nooruse 1, Tartu, Estonia; Molecular Biology Department, Faculty of Biology, M.V. Lomonosov Moscow State University, 1/12 Leninskie Gory, 119991 Moscow, Russia
| | - Gemma C Atkinson
- University of Tartu, Institute of Technology, Nooruse 1, Tartu, Estonia
| | - Sergey Levitskii
- Molecular Biology Department, Faculty of Biology, M.V. Lomonosov Moscow State University, 1/12 Leninskie Gory, 119991 Moscow, Russia
| | - Nikolay Zenkin
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4AX, United Kingdom
| | - Tanel Tenson
- University of Tartu, Institute of Technology, Nooruse 1, Tartu, Estonia
| | - Vasili Hauryliuk
- University of Tartu, Institute of Technology, Nooruse 1, Tartu, Estonia; Department of Molecular Biology, Umeå University, Umeå, Sweden; Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, Umeå, Sweden.
| | - Piotr Kamenski
- Molecular Biology Department, Faculty of Biology, M.V. Lomonosov Moscow State University, 1/12 Leninskie Gory, 119991 Moscow, Russia.
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Funes S, Westerburg H, Jaimes-Miranda F, Woellhaf MW, Aguilar-Lopez JL, Janßen L, Bonnefoy N, Kauff F, Herrmann JM. Partial suppression of Oxa1 mutants by mitochondria-targeted signal recognition particle provides insights into the evolution of the cotranslational insertion systems. FEBS J 2013. [PMID: 23198851 DOI: 10.1111/febs.12082] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The biogenesis of hydrophobic membrane proteins involves their cotranslational membrane integration in order to prevent their unproductive aggregation. In the cytosol of bacteria and eukaryotes, membrane targeting of ribosomes that synthesize membrane proteins is achieved by signal recognition particles (SRPs) and their cognate membrane-bound receptors. As is evident from the genomes of fully sequenced eukaryotes, mitochondria generally lack an SRP system. Instead, mitochondrial ribosomes are physically associated with the protein insertion machinery in the inner membrane. Accordingly, deletion of ribosome-binding sites on the Oxa1 insertase and the Mba1 ribosome receptor in yeast leads to severe defects in cotranslational protein insertion and results in respiration-deficient mutants. In this study, we expressed mitochondria-targeted versions of the bacterial SRP protein Ffh and its receptor FtsY in these yeast mutants. Interestingly, Ffh was found to bind to the large subunit of mitochondrial ribosomes, and could relieve, to some degree, the defect of these insertion mutants. Although FtsY could also bind to mitochondrial membranes, it did not improve membrane protein biogenesis in this strain, presumably because of its inability to interact with Ffh. Hence, mitochondrial ribosomes are still able to interact physically and functionally with the bacterial SRP system. Our observations are consistent with a model according to which the protein insertion system in mitochondria evolved in three steps. The loss of genes for hydrophilic polypeptides (step 1) allowed the development of ribosome-binding sites on membrane proteins (step 2), which finally made the existence of an SRP-mediated system dispensable (step 3).
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Affiliation(s)
- Soledad Funes
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Ciudad Universitaria, Universidad Nacional Autónoma de México, Distrito Federal, Mexico.
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Abstract
Mammalian mitochondria contain their own genome that encodes mRNAs for thirteen essential subunits of the complexes performing oxidative phosphorylation as well as the RNA components (two rRNAs and 22 tRNAs) needed for their translation in mitochondria. All RNA species are produced from single polycistronic precursor RNAs, yet the relative concentrations of various RNAs differ significantly. This underscores the essential role of post-transcriptional mechanisms that control the maturation, stability and translation of mitochondrial RNAs. The present review provides a detailed summary on the role of RNA maturation in the regulation of mitochondrial gene expression, focusing mainly on messenger RNA polyadenylation and stability control. Furthermore, the role of mitochondrial ribosomal RNA stability, processing and modifications in the biogenesis of the mitochondrial ribosome is discussed.
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Soto IC, Fontanesi F, Liu J, Barrientos A. Biogenesis and assembly of eukaryotic cytochrome c oxidase catalytic core. BIOCHIMICA ET BIOPHYSICA ACTA 2012; 1817:883-97. [PMID: 21958598 PMCID: PMC3262112 DOI: 10.1016/j.bbabio.2011.09.005] [Citation(s) in RCA: 159] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2011] [Revised: 09/07/2011] [Accepted: 09/12/2011] [Indexed: 10/17/2022]
Abstract
Eukaryotic cytochrome c oxidase (COX) is the terminal enzyme of the mitochondrial respiratory chain. COX is a multimeric enzyme formed by subunits of dual genetic origin which assembly is intricate and highly regulated. The COX catalytic core is formed by three mitochondrial DNA encoded subunits, Cox1, Cox2 and Cox3, conserved in the bacterial enzyme. Their biogenesis requires the action of messenger-specific and subunit-specific factors which facilitate the synthesis, membrane insertion, maturation or assembly of the core subunits. The study of yeast strains and human cell lines from patients carrying mutations in structural subunits and COX assembly factors has been invaluable to identify these ancillary factors. Here we review the current state of knowledge of the biogenesis and assembly of the eukaryotic COX catalytic core and discuss the degree of conservation of the players and mechanisms operating from yeast to human. This article is part of a Special Issue entitled: Biogenesis/Assembly of Respiratory Enzyme Complexes.
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Affiliation(s)
- Ileana C. Soto
- Department of Biochemistry & Molecular Biology, University of Miami Miller School of Medicine. Miami, FL
| | - Flavia Fontanesi
- Department of Neurology. University of Miami Miller School of Medicine. Miami, FL
| | - Jingjing Liu
- Department of Biochemistry & Molecular Biology, University of Miami Miller School of Medicine. Miami, FL
| | - Antoni Barrientos
- Department of Biochemistry & Molecular Biology, University of Miami Miller School of Medicine. Miami, FL
- Department of Neurology. University of Miami Miller School of Medicine. Miami, FL
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Atkinson GC, Kuzmenko A, Kamenski P, Vysokikh MY, Lakunina V, Tankov S, Smirnova E, Soosaar A, Tenson T, Hauryliuk V. Evolutionary and genetic analyses of mitochondrial translation initiation factors identify the missing mitochondrial IF3 in S. cerevisiae. Nucleic Acids Res 2012; 40:6122-34. [PMID: 22457064 PMCID: PMC3401457 DOI: 10.1093/nar/gks272] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
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.
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Herrmann JM, Woellhaf MW, Bonnefoy N. Control of protein synthesis in yeast mitochondria: the concept of translational activators. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1833:286-94. [PMID: 22450032 DOI: 10.1016/j.bbamcr.2012.03.007] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2012] [Revised: 03/01/2012] [Accepted: 03/08/2012] [Indexed: 12/18/2022]
Abstract
Mitochondria contain their own genome which codes for a small number of proteins. Most mitochondrial translation products are part of the membrane-embedded reaction centers of the respiratory chain complexes. In the yeast Saccharomyces cerevisiae, the expression of these proteins is regulated by translational activators that bind mitochondrial mRNAs, in most cases to their 5'-untranslated regions, and each mitochondrial mRNA appears to have its own translational activator(s). Recent studies showed that these translational activators can be part of feedback control loops which only permit translation if the downstream assembly of nascent translation products can occur. In several cases, the accumulation of a non-assembled protein prevents further synthesis of this protein but not translation in general. These control loops prevent the synthesis of potentially harmful assembly intermediates of the reaction centers of mitochondrial enzymes. Since such regulatory feedback loops only work if translation occurs in the compartment in which the complexes of the respiratory chain are assembled, these control mechanisms require the presence of a translation machinery in mitochondria. This might explain why eukaryotic cells maintained DNA in mitochondria during the last two billion years of evolution. This review gives an overview of the mitochondrial translation system and summarizes the current knowledge on translational activators and their role in the regulation of mitochondrial protein synthesis. This article is part of a Special Issue entitled: Protein import and quality control in mitochondria and plastids.
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Affiliation(s)
- Johannes M Herrmann
- Cell Biology, Erwin-Schrödinger-Strasse 13, University of Kaiserslautern, 67663 Kaiserslautern, Germany.
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Kühl I, Fox TD, Bonnefoy N. Schizosaccharomyces pombe homologs of the Saccharomyces cerevisiae mitochondrial proteins Cbp6 and Mss51 function at a post-translational step of respiratory complex biogenesis. Mitochondrion 2012; 12:381-90. [PMID: 22349564 DOI: 10.1016/j.mito.2012.02.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2011] [Revised: 01/31/2012] [Accepted: 02/03/2012] [Indexed: 11/18/2022]
Abstract
Complexes III and IV of the mitochondrial respiratory chain contain a few key subunits encoded by the mitochondrial genome. In Saccharomyces cerevisiae, fifteen mRNA-specific translational activators control mitochondrial translation, of which five are conserved in Schizosaccharomyces pombe. These include homologs of Cbp3, Cbp6 and Mss51 that participate in translation and the post-translational steps leading to the assembly of respiratory complexes III and IV. In this study we show that in contrast to budding yeast, Cbp3, Cbp6 and Mss51 from S. pombe are not required for the translation of mitochondrial mRNAs, but fulfill post-translational functions, thus probably accounting for their conservation.
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Affiliation(s)
- Inge Kühl
- Centre de Génétique Moléculaire du CNRS, UPR 3404, FRC3115, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
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17
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Hoppins S, Collins SR, Cassidy-Stone A, Hummel E, Devay RM, Lackner LL, Westermann B, Schuldiner M, Weissman JS, Nunnari J. A mitochondrial-focused genetic interaction map reveals a scaffold-like complex required for inner membrane organization in mitochondria. ACTA ACUST UNITED AC 2011; 195:323-40. [PMID: 21987634 PMCID: PMC3198156 DOI: 10.1083/jcb.201107053] [Citation(s) in RCA: 346] [Impact Index Per Article: 26.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Statement MITO-MAP, a high-density genetic interaction map in budding yeast, identifies a mitochondrial inner membrane–associated complex that promotes normal mitochondrial membrane organization and morphology. To broadly explore mitochondrial structure and function as well as the communication of mitochondria with other cellular pathways, we constructed a quantitative, high-density genetic interaction map (the MITO-MAP) in Saccharomyces cerevisiae. The MITO-MAP provides a comprehensive view of mitochondrial function including insights into the activity of uncharacterized mitochondrial proteins and the functional connection between mitochondria and the ER. The MITO-MAP also reveals a large inner membrane–associated complex, which we term MitOS for mitochondrial organizing structure, comprised of Fcj1/Mitofilin, a conserved inner membrane protein, and five additional components. MitOS physically and functionally interacts with both outer and inner membrane components and localizes to extended structures that wrap around the inner membrane. We show that MitOS acts in concert with ATP synthase dimers to organize the inner membrane and promote normal mitochondrial morphology. We propose that MitOS acts as a conserved mitochondrial skeletal structure that differentiates regions of the inner membrane to establish the normal internal architecture of mitochondria.
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Affiliation(s)
- Suzanne Hoppins
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, USA
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18
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Gruschke S, Kehrein K, Römpler K, Gröne K, Israel L, Imhof A, Herrmann JM, Ott M. Cbp3-Cbp6 interacts with the yeast mitochondrial ribosomal tunnel exit and promotes cytochrome b synthesis and assembly. ACTA ACUST UNITED AC 2011; 193:1101-14. [PMID: 21670217 PMCID: PMC3115798 DOI: 10.1083/jcb.201103132] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
A complex specifically required for the biogenesis of the respiratory chain component cytochrome b binds to the tunnel exit of yeast mitochondrial ribosomes to coordinate protein synthesis and assembly. Mitochondria contain their own genetic system to express a small number of hydrophobic polypeptides, including cytochrome b, an essential subunit of the bc1 complex of the respiratory chain. In this paper, we show in yeast that Cbp3, a bc1 complex assembly factor, and Cbp6, a regulator of cytochrome b translation, form a complex that associates with the polypeptide tunnel exit of mitochondrial ribosomes and that exhibits two important functions in the biogenesis of cytochrome b. On the one hand, the interaction of Cbp3 and Cbp6 with mitochondrial ribosomes is necessary for efficient translation of cytochrome b transcript. On the other hand, the Cbp3–Cbp6 complex interacts directly with newly synthesized cytochrome b in an assembly intermediate that is not ribosome bound and that contains the assembly factor Cbp4. Our results suggest that synthesis of cytochrome b occurs preferentially on those ribosomes that have the Cbp3–Cbp6 complex bound to their tunnel exit, an arrangement that may ensure tight coordination of cytochrome b synthesis and assembly.
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Affiliation(s)
- Steffi Gruschke
- Abteilung Membranbiogenese and 2 Abteilung Membranbiogenese Zellbiologie, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
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19
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Graef M, Nunnari J. Mitochondria regulate autophagy by conserved signalling pathways. EMBO J 2011; 30:2101-14. [PMID: 21468027 DOI: 10.1038/emboj.2011.104] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2010] [Accepted: 03/16/2011] [Indexed: 11/10/2022] Open
Abstract
Autophagy is a conserved degradative process that is crucial for cellular homeostasis and cellular quality control via the selective removal of subcellular structures such as mitochondria. We demonstrate that a regulatory link exists between mitochondrial function and autophagy in Saccharomyces cerevisiae. During amino-acid starvation, the autophagic response consists of two independent regulatory arms-autophagy gene induction and autophagic flux-and our analysis indicates that mitochondrial respiratory deficiency severely compromises both. We show that the evolutionarily conserved protein kinases Atg1, target of rapamycin kinase complex I, and protein kinase A (PKA) regulate autophagic flux, whereas autophagy gene induction depends solely on PKA. Within this regulatory network, mitochondrial respiratory deficiency suppresses autophagic flux, autophagy gene induction, and recruitment of the Atg1-Atg13 kinase complex to the pre-autophagosomal structure by stimulating PKA activity. Our findings indicate an interrelation of two common risk factors-mitochondrial dysfunction and autophagy inhibition-for ageing, cancerogenesis, and neurodegeneration.
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Affiliation(s)
- Martin Graef
- Department of Molecular and Cellular Biology, Davis University of California, Davis, CA, USA
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20
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Ott M, Herrmann JM. Co-translational membrane insertion of mitochondrially encoded proteins. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1803:767-75. [PMID: 19962410 DOI: 10.1016/j.bbamcr.2009.11.010] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2009] [Revised: 11/18/2009] [Accepted: 11/25/2009] [Indexed: 11/29/2022]
Abstract
The components of the mitochondrial proteome represent a mosaic of dual genetic origin: while most mitochondrial proteins are encoded by nuclear genes and imported into the organelle following synthesis in the cytosol, a small number of proteins is encoded by the mitochondrial genome. Though small in number, mitochondrial translation products are vital for cellular functionality as these proteins represent the core subunits of the respiratory chain and the ATPase which produce the vast majority of the cellular ATP. Mitochondrial translation products are almost exclusively highly hydrophobic polypeptides which are inserted into the inner membrane in the course of their synthesis. The machinery that mediates membrane insertion in mitochondria is deduced from that of their bacterial ancestors and hence shows profound similarities to the insertion machinery of prokaryotes. However, the specialization on the production of a very small set of translation products drove a severe reduction in the complexity of this system. The insertase Oxa1 forms the central component of the insertion machinery. Oxa1 directly binds to mitochondrial ribosomes and, together with the inner membrane protein Mba1, aligns the polypeptide exit tunnel of the ribosome with the insertion site at the inner membrane. The specific hallmarks and the critical components of this machinery are discussed in this review article.
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Affiliation(s)
- Martin Ott
- Cell Biology, University of Kaiserslautern, 67663 Kaiserslautern, Germany
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21
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Perez-Martinez X, Butler CA, Shingu-Vazquez M, Fox TD. Dual functions of Mss51 couple synthesis of Cox1 to assembly of cytochrome c oxidase in Saccharomyces cerevisiae mitochondria. Mol Biol Cell 2009; 20:4371-80. [PMID: 19710419 DOI: 10.1091/mbc.e09-06-0522] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Functional interactions of the translational activator Mss51 with both the mitochondrially encoded COX1 mRNA 5'-untranslated region and with newly synthesized unassembled Cox1 protein suggest that it has a key role in coupling Cox1 synthesis with assembly of cytochrome c oxidase. Mss51 is present at levels that are near rate limiting for expression of a reporter gene inserted at COX1 in mitochondrial DNA, and a substantial fraction of Mss51 is associated with Cox1 protein in assembly intermediates. Thus, sequestration of Mss51 in assembly intermediates could limit Cox1 synthesis in wild type, and account for the reduced Cox1 synthesis caused by most yeast mutations that block assembly. Mss51 does not stably interact with newly synthesized Cox1 in a mutant lacking Cox14, suggesting that the failure of nuclear cox14 mutants to decrease Cox1 synthesis, despite their inability to assemble cytochrome c oxidase, is due to a failure to sequester Mss51. The physical interaction between Mss51 and Cox14 is dependent upon Cox1 synthesis, indicating dynamic assembly of early cytochrome c oxidase intermediates nucleated by Cox1. Regulation of COX1 mRNA translation by Mss51 seems to be an example of a homeostatic mechanism in which a positive effector of gene expression interacts with the product it regulates in a posttranslational assembly process.
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Affiliation(s)
- Xochitl Perez-Martinez
- Departamento de Bioquímica, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México D.F. 04510, México
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22
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Zeng X, Hourset A, Tzagoloff A. The Saccharomyces cerevisiae ATP22 gene codes for the mitochondrial ATPase subunit 6-specific translation factor. Genetics 2006; 175:55-63. [PMID: 17110482 PMCID: PMC1775023 DOI: 10.1534/genetics.106.065821] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mutations in the Saccharomyces cerevisiae ATP22 gene were previously shown to block assembly of the F0 component of the mitochondrial proton-translocating ATPase. Further inquiries into the function of Atp22p have revealed that it is essential for translation of subunit 6 of the mitochondrial ATPase. The mutant phenotype can be partially rescued by the presence in the same cell of wild-type mitochondrial DNA and a rho- deletion genome in which the 5'-UTR, first exon, and first intron of COX1 are fused to the fourth codon of ATP6. The COX1/ATP6 gene is transcribed and processed to the mature mRNA by splicing of the COX1 intron from the precursor. The hybrid protein translated from the novel mRNA is proteolytically cleaved at the normal site between residues 10 and 11 of the subunit 6 precursor, causing the release of the polypeptide encoded by the COX1 exon. The ability of the rho- suppressor genome to express subunit 6 in an atp22 null mutant constitutes strong evidence that translation of subunit 6 depends on the interaction of Atp22p with the 5'-UTR of the ATP6 mRNA.
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Affiliation(s)
- Xiaomei Zeng
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA
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23
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Fontanesi F, Soto IC, Horn D, Barrientos A. Assembly of mitochondrial cytochrome c-oxidase, a complicated and highly regulated cellular process. Am J Physiol Cell Physiol 2006; 291:C1129-47. [PMID: 16760263 DOI: 10.1152/ajpcell.00233.2006] [Citation(s) in RCA: 190] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cytochrome c-oxidase (COX), the terminal enzyme of the mitochondrial respiratory chain, plays a key role in the regulation of aerobic production of energy. Biogenesis of eukaryotic COX involves the coordinated action of two genomes. Three mitochondrial DNA-encoded subunits form the catalytic core of the enzyme, which contains metal prosthetic groups. Another 10 subunits encoded in the nuclear DNA act as a protective shield surrounding the core. COX biogenesis requires the assistance of >20 additional nuclear-encoded factors acting at all levels of the process. Expression of the mitochondrial-encoded subunits, expression and import of the nuclear-encoded subunits, insertion of the structural subunits into the mitochondrial inner membrane, addition of prosthetic groups, assembly of the holoenzyme, further maturation to form a dimer, and additional assembly into supercomplexes are all tightly regulated processes in a nuclear-mitochondrial-coordinated fashion. Such regulation ensures the building of a highly efficient machine able to catalyze the safe transfer of electrons from cytochrome c to molecular oxygen and ultimately facilitate the aerobic production of ATP. In this review, we will focus on describing and analyzing the present knowledge about the different regulatory checkpoints in COX assembly and the dynamic relationships between the different factors involved in the process. We have used information mostly obtained from the suitable yeast model, but also from bacterial and animal systems, by means of large-scale genetic, molecular biology, and physiological approaches and by integrating information concerning individual elements into a cellular system network.
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Affiliation(s)
- Flavia Fontanesi
- Departments of Neurology, The John T. Macdonald Foundation Center for Medical Genetics, University of Miami Miller School of Medicine, Miami, Florida 33136, USA
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24
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Ott M, Prestele M, Bauerschmitt H, Funes S, Bonnefoy N, Herrmann JM. Mba1, a membrane-associated ribosome receptor in mitochondria. EMBO J 2006; 25:1603-10. [PMID: 16601683 PMCID: PMC1440829 DOI: 10.1038/sj.emboj.7601070] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2006] [Accepted: 03/09/2006] [Indexed: 11/09/2022] Open
Abstract
The genome of mitochondria encodes a small number of very hydrophobic polypeptides that are inserted into the inner membrane in a cotranslational reaction. The molecular process by which mitochondrial ribosomes are recruited to the membrane is poorly understood. Here, we show that the inner membrane protein Mba1 binds to the large subunit of mitochondrial ribosomes. It thereby cooperates with the C-terminal ribosome-binding domain of Oxa1, which is a central component of the insertion machinery of the inner membrane. In the absence of both Mba1 and the C-terminus of Oxa1, mitochondrial translation products fail to be properly inserted into the inner membrane and serve as substrates of the matrix chaperone Hsp70. We propose that Mba1 functions as a ribosome receptor that cooperates with Oxa1 in the positioning of the ribosome exit site to the insertion machinery of the inner membrane.
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Affiliation(s)
- Martin Ott
- Institut für Physiologische Chemie, Universität München, München, Germany
| | - Martin Prestele
- Institut für Physiologische Chemie, Universität München, München, Germany
| | - Heike Bauerschmitt
- Institut für Physiologische Chemie, Universität München, München, Germany
| | - Soledad Funes
- Institut für Physiologische Chemie, Universität München, München, Germany
| | | | - Johannes M Herrmann
- Institut für Physiologische Chemie, Universität München, München, Germany
- Institut für Physiologische Chemie, Universität München, Butenandtstrasse 5, München 81377, Germany. Tel.: +49 89 2180 77122; Fax: +49 89 2180 77093; E-mail:
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25
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Barros MH, Myers AM, Van Driesche S, Tzagoloff A. COX24 codes for a mitochondrial protein required for processing of the COX1 transcript. J Biol Chem 2005; 281:3743-51. [PMID: 16339141 DOI: 10.1074/jbc.m510778200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In most strains of Saccharomyces cerevisiae the mitochondrial gene COX1, for subunit 1 of cytochrome oxidase, contains multiple exons and introns. Processing of COX1 primary transcript requires accessory proteins factors, some of which are encoded by nuclear genes and others by reading frames residing in some of the introns of the COX1 and COB genes. Here we show that the low molecular weight protein product of open reading frame YLR204W, for which we propose the name COX24, is also involved in processing of COX1 RNA intermediates. The growth defect of cox24 mutants is partially rescued in strains harboring mitochondrial DNA lacking introns. Northern blot analyses of mitochondrial transcripts indicate cox24 null mutants to be blocked in processing of introns aI2 and aI3. The dependence of intron aI3 excision on Cox24p is also supported by the growth properties of the cox24 mutant harboring mitochondrial DNA with different intron compositions. The intermediate phenotype of the cox24 mutant in the background of intronless mitochondrial DNA, however, suggests that in addition to its role in splicing of the COX1 pre-mRNA, Cox24p still has another function. Based on the analysis of a cox14-cox24 double mutant, we propose that the other function of Cox24p is related to translation of the COX1 mRNA.
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Affiliation(s)
- Mario H Barros
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA
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26
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Kleidon J, Plesofsky N, Brambl R. Transcripts and transcript-binding proteins in mitochondria of Neurospora crassa. Mitochondrion 2005; 2:345-60. [PMID: 16120332 DOI: 10.1016/s1567-7249(03)00002-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2002] [Revised: 10/25/2002] [Accepted: 12/16/2002] [Indexed: 10/27/2022]
Abstract
We analyzed expression elements of three disparate groups of mitochondrial genes in Neurospora crassa, apocytochrome b (COB), cytochrome c oxidase 1 (COX1), and the clustered ATP8-ATP6-mtATP9-COX2. To identify promoter sequences we employed the published N. crassa consensus sequence for COB and rRNA genes, and we found closely related sequences within the 5'-regions of both COX1 and the ATP8-COX2 transcriptional units. We determined that the mature COX1 RNA includes two flanking unassigned reading frame (URF) sequences, but the 3'-flanking ND1 is not included in the COX1 mRNA. The ATP8-ATP6-mtATP9-COX2 polycistronic transcript does not include an adjacent 5'-URF sequence. Primer extension analysis showed one likely 5'-end for the COX1 transcript, which is 73 nucleotides downstream of the consensus promoter sequence and is the first nucleotide 3' of the sequence for the tRNA(cys). Primer extension analysis and S1 nuclease mapping of the ATP8-COX2 RNA showed that the 5'-end for this transcript is the first nucleotide 3' of the consensus promoter sequence. We performed gel-shift experiments to detect proteins in mitochondria that bind to transcripts as possible regulatory proteins. The 5'-untranslated region (UTR) RNAs of COB, COX1, and ATP8-COX2 appear to bind both unique proteins and an overlapping group of two to four proteins of approximately 155-45 M(r). We successively deleted regions of the RNA 5'-UTRs to identify sequences that bound these proteins. Similar predicted stem-loop secondary structures were detected in the protein-binding regions of all three UTRs.
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Affiliation(s)
- Jill Kleidon
- Department of Plant Biology and Plant Molecular Genetics Institute, The University of Minnesota, 220 BioSciences Center, 1445 Gortner Avenue, Saint Paul, MN 55108, USA
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27
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Khalimonchuk O, Rödel G. Biogenesis of cytochrome c oxidase. Mitochondrion 2005; 5:363-88. [PMID: 16199211 DOI: 10.1016/j.mito.2005.08.002] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2005] [Accepted: 08/10/2005] [Indexed: 11/20/2022]
Abstract
Cytochrome c oxidase (COX), the terminal enzyme of electron transport chains in some prokaryotes and in mitochondria, has been characterized in detail over many years. Recently, a number of new data on structural and functional aspects as well as on COX biogenesis emerged. COX biogenesis includes a variety of steps starting from translation to the formation of the mature complex. Each step involves a set of specific factors that assist translation of subunits, their translocation across membranes, insertion of essential cofactors, assembly and final maturation of the enzyme. In this review, we focus on the organization and biogenesis of COX.
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Affiliation(s)
- Oleh Khalimonchuk
- Institut für Genetik, Technische Universität Dresden, 01062 Dresden, Germany
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28
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Herrmann JM, Funes S. Biogenesis of cytochrome oxidase—Sophisticated assembly lines in the mitochondrial inner membrane. Gene 2005; 354:43-52. [PMID: 15905047 DOI: 10.1016/j.gene.2005.03.017] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2005] [Revised: 02/02/2005] [Accepted: 03/23/2005] [Indexed: 11/18/2022]
Abstract
Biogenesis of the cytochrome oxidase complex in the mitochondrial inner membrane depends on the concerted action of a variety of proteins. Recent studies shed light on this biological assembly process revealing an astonishingly complex procedure by which the different subunits of the enzymes are put together and the required cofactors are supplied. In this review we present a hypothetical model for the assembly process of cytochrome oxidase based on the current knowledge of the functions of specific assembly factors. According to this model the two largest subunits of the complex are first equipped with their respective cofactors on independent assembly lines. Prior to their assembly with the residual subunits that complete the whole complex, these two subcomplexes remain bound to substrate-specific chaperones. We propose that these chaperones, Mss51 for subunit 1 and Cox20 for subunit 2, control the coordinate assembly process to prevent potentially harmful redox reactions of unassembled or misassembled subunits.
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Affiliation(s)
- Johannes M Herrmann
- Institute of Physiological Chemistry, Butenandtstrasse 5, 81377 München, University of Munich, Germany.
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29
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Demlow CM, Fox TD. Activity of mitochondrially synthesized reporter proteins is lower than that of imported proteins and is increased by lowering cAMP in glucose-grown Saccharomyces cerevisiae cells. Genetics 2004; 165:961-74. [PMID: 14668357 PMCID: PMC1462836 DOI: 10.1093/genetics/165.3.961] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
We selected for increased phenotypic expression of a synthetic cox2::arg8m-G66S reporter gene inserted into Saccharomyces cerevisiae mtDNA in place of COX2. Recessive mutations in ras2 and cyr1, as well as elevated dosage of PDE2, allowed cox2::arg8m-G66S to support Arg prototrophy. Each of these genetic alterations should decrease cellular cAMP levels. The resulting signal was transduced through redundant action of the three cAMP-dependent protein kinases, TPK1, TPK2, and TPK3. ras2 had little or no effect on the level of wild-type Arg8p encoded by cox2::ARG8m, but did increase Arg8p activity, as judged by growth phenotype. ras2 also caused increased fluorescence in cells carrying the synthetic cox3::GFPm reporter in mtDNA, but had little effect on the steady-state level of GFP polypeptide detected immunologically. Thus, decreased cAMP levels did not affect the synthesis of mitochondrially coded protein reporters in glucose-grown cells, but rather elevated activities in the matrix that promote efficient folding. Furthermore, we show that when Arg8p is synthesized in the cytoplasm and imported into mitochondria, it has greater activity than when it is synthesized in the matrix. Thus, mitochondrially synthesized proteins may not have the same access to matrix chaperones as cytoplasmically synthesized proteins emerging from the import apparatus.
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Affiliation(s)
- Christina M Demlow
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853, USA
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30
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Bullerwell CE, Forget L, Lang BF. Evolution of monoblepharidalean fungi based on complete mitochondrial genome sequences. Nucleic Acids Res 2003; 31:1614-23. [PMID: 12626702 PMCID: PMC152866 DOI: 10.1093/nar/gkg264] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
We have determined the complete mitochondrial DNA (mtDNA) sequences of three chytridiomycete fungi, Monoblepharella15, Harpochytrium94 and Harpochytrium105. Our phylogenetic analysis based on concatenated mitochondrial protein sequences confirms the placement of Mono blepharella15 together with Harpochytrium spp. and Hyaloraphidium curvatum within the taxonomic order Monoblepharidales, with overwhelming support. These four mtDNA sequences encode the standard fungal mitochondrial gene complement and, like certain other chytridiomycete fungi, encode a reduced complement of 7-9 tRNAs, some of which require 5'-tRNA editing to be functional. Highly conserved sequence elements were identified upstream of almost all protein-coding genes in the mtDNAs of Monoblepharella15 and both Harpochytrium species. Finally, a guanosine residue is conserved upstream of the predicted ATG or GTG start codons of almost every protein-coding gene in these genomes. The appearance of this G residue correlates with the presence of a non-canonical cytosine residue at position 37 in the anticodon loop of the mitochondrial initiator tRNAs. Based on the unorthodox features in these four genomes, we propose that a 4 bp interaction between the CAUC anticodon of these tRNAs and GAUG/GGUG codons is involved in translation initiation in monoblepharidalean mitochondria. Intriguingly, a similar interaction may also be involved in mitochondrial translation initiation in the sea anemone Metridium senile.
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Affiliation(s)
- C E Bullerwell
- Program in Evolutionary Biology, Canadian Institute for Advanced Research, Département de Biochimie, Université de Montréal, 2900 Boulevard Edouard-Montpetit, Montréal, Québec H3T 1J4, Canada
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31
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Evolution of the Fungi and their Mitochondrial Genomes. ACTA ACUST UNITED AC 2003. [DOI: 10.1016/s1874-5334(03)80010-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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32
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Naithani S, Saracco SA, Butler CA, Fox TD. Interactions among COX1, COX2, and COX3 mRNA-specific translational activator proteins on the inner surface of the mitochondrial inner membrane of Saccharomyces cerevisiae. Mol Biol Cell 2003; 14:324-33. [PMID: 12529447 PMCID: PMC140248 DOI: 10.1091/mbc.e02-08-0490] [Citation(s) in RCA: 121] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2002] [Accepted: 09/20/2002] [Indexed: 11/11/2022] Open
Abstract
The core of the cytochrome c oxidase complex is composed of its three largest subunits, Cox1p, Cox2p, and Cox3p, which are encoded in mitochondrial DNA of Saccharomyces cerevisiae and inserted into the inner membrane from the inside. Mitochondrial translation of the COX1, COX2, and COX3 mRNAs is activated mRNA specifically by the nuclearly coded proteins Pet309p, Pet111p, and the concerted action of Pet54p, Pet122p, and Pet494p, respectively. Because the translational activators recognize sites in the 5'-untranslated leaders of these mRNAs and because untranslated mRNA sequences contain information for targeting their protein products, the activators are likely to play a role in localizing translation. Herein, we report physical associations among the mRNA-specific translational activator proteins, located on the matrix side of the inner membrane. These interactions, detected by coimmune precipitation and by two-hybrid experiments, suggest that the translational activator proteins could be organized on the surface of the inner membrane such that synthesis of Cox1p, Cox2p, and Cox3p would be colocalized in a way that facilitates assembly of the core of the cytochrome c oxidase complex. In addition, we found interactions between Nam1p/Mtf2p and the translational activators, suggesting an organized delivery of mitochondrial mRNAs to the translation system.
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Affiliation(s)
- Sushma Naithani
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703, USA
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33
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Green-Willms NS, Butler CA, Dunstan HM, Fox TD. Pet111p, an inner membrane-bound translational activator that limits expression of the Saccharomyces cerevisiae mitochondrial gene COX2. J Biol Chem 2001; 276:6392-7. [PMID: 11106667 DOI: 10.1074/jbc.m009856200] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The protein specified by the Saccharomyces cerevisiae nuclear gene PET111 specifically activates translation of the mitochondrially coded mRNA for cytochrome c oxidase subunit II (Cox2p). We found Pet111p specifically in mitochondria of both wild-type cells and cells expressing a chromosomal gene for a functional epitope-tagged form of Pet111p. Pet111p was associated with mitochondrial membranes and was highly resistant to extraction with alkaline carbonate. Pet111p was protected from proteolytic digestion by the mitochondrial inner membrane. Thus, it is exposed only on the matrix side, where it could participate directly in organellar translation and localize Cox2p synthesis by virtue of its functional interaction with the COX2 mRNA 5'-untranslated leader. We also found that Pet111p is present at levels limiting the synthesis of Cox2p by examining the effect of altered PET111 gene dosage in the nucleus on expression of a reporter gene, cox2::ARG8(m), that was inserted into mitochondrial DNA. The level of the reporter protein, Arg8p, was one-half that of wild type in a diploid strain heterozygous for a pet111 deletion mutation, whereas it was increased 2.8-fold in a strain bearing extra copies of PET111 on a high-copy plasmid. Thus, Pet111p could play dual roles in both membrane localization and regulation of Cox2p synthesis within mitochondria.
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Affiliation(s)
- N S Green-Willms
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703, USA
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Proteins Involved in Biogenesis of the Thylakoid Membrane. REGULATION OF PHOTOSYNTHESIS 2001. [DOI: 10.1007/0-306-48148-0_9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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35
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Tzschoppe K, Kohlwein SD, Rödel G. Yeast translational activator Cbs2p: mitochondrial targeting and effect of overexpression. Biol Chem 2000; 381:1175-83. [PMID: 11209752 DOI: 10.1515/bc.2000.145] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The yeast translational activator protein Cbs2p is imported into mitochondria without obvious proteolytic processing. To test the importance of amino-terminal amino acids for mitochondrial targeting we fused varying portions of the N-terminus with green fluorescent protein and examined the intracellular distribution of the reporter protein. We show that the 25 N-terminal amino acids are sufficient to direct the majority of the fusion protein into mitochondria. Cbs2p derivatives lacking 9 to 35 amino acids from the N-terminus fail to complement the respiratory deficiency of a deltacbs2 strain, but are still imported into mitochondria. Therefore Cbs2p contains at least one independent mitochondrial targeting information in addition to the N-terminal signal. We further analyzed the effect of over-expression of Cbs2p on mitochondrial function. Elevated concentrations of Cbs2p lead to slightly impaired mitochondrial gene expression, probably as the result of the formation of inactive Cbs2p aggregates.
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Affiliation(s)
- K Tzschoppe
- Institut für Genetik, Technische Universität Dresden, Germany
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36
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Costanzo MC, Bonnefoy N, Williams EH, Clark-Walker GD, Fox TD. Highly diverged homologs of Saccharomyces cerevisiae mitochondrial mRNA-specific translational activators have orthologous functions in other budding yeasts. Genetics 2000; 154:999-1012. [PMID: 10757749 PMCID: PMC1460983 DOI: 10.1093/genetics/154.3.999] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Translation of mitochondrially coded mRNAs in Saccharomyces cerevisiae depends on membrane-bound mRNA-specific activator proteins, whose targets lie in the mRNA 5'-untranslated leaders (5'-UTLs). In at least some cases, the activators function to localize translation of hydrophobic proteins on the inner membrane and are rate limiting for gene expression. We searched unsuccessfully in divergent budding yeasts for orthologs of the COX2- and COX3-specific translational activator genes, PET111, PET54, PET122, and PET494, by direct complementation. However, by screening for complementation of mutations in genes adjacent to the PET genes in S. cerevisiae, we obtained chromosomal segments containing highly diverged homologs of PET111 and PET122 from Saccharomyces kluyveri and of PET111 from Kluyveromyces lactis. All three of these genes failed to function in S. cerevisiae. We also found that the 5'-UTLs of the COX2 and COX3 mRNAs of S. kluyveri and K. lactis have little similarity to each other or to those of S. cerevisiae. To determine whether the PET111 and PET122 homologs carry out orthologous functions, we deleted them from the S. kluyveri genome and deleted PET111 from the K. lactis genome. The pet111 mutations in both species prevented COX2 translation, and the S. kluyveri pet122 mutation prevented COX3 translation. Thus, while the sequences of these translational activator proteins and their 5'-UTL targets are highly diverged, their mRNA-specific functions are orthologous.
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Affiliation(s)
- M C Costanzo
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703, USA
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37
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Sanchirico ME, Fox TD, Mason TL. Accumulation of mitochondrially synthesized Saccharomyces cerevisiae Cox2p and Cox3p depends on targeting information in untranslated portions of their mRNAs. EMBO J 1998; 17:5796-804. [PMID: 9755179 PMCID: PMC1170907 DOI: 10.1093/emboj/17.19.5796] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The essential products of the yeast mitochondrial translation system are seven hydrophobic membrane proteins and Var1p, a hydrophilic protein in the small ribosomal subunit. Translation of the membrane proteins depends on nuclearly encoded, mRNA-specific translational activators that recognize the 5'-untranslated leaders of their target mRNAs. These translational activators are themselves membrane associated and could therefore tether translation to the inner membrane. In this study, we tested whether chimeric mRNAs with the untranslated sequences normally present on the mRNA encoding soluble Var1p, can direct functional expression of coding sequences specifying the integral membrane proteins Cox2p and Cox3p. DNA sequences specifying these chimeric mRNAs were inserted into mtDNA at the VAR1 locus and expressed in strains containing a nuclearly localized plasmid that supplies a functional form of Var1p, imported from the cytoplasm. Although cells expressing these chimeric mRNAs actively synthesized both membrane proteins, they were severely deficient in cytochrome c oxidase activity and in the accumulation of Cox2p and Cox3p, respectively. These data strongly support the physiological importance of interactions between membrane-bound mRNA-specific translational activators and the native 5'-untranslated leaders of the COX2 and COX3 mRNAs for localizing productive synthesis of Cox2p and Cox3p to the inner membrane.
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Affiliation(s)
- M E Sanchirico
- Department of Biochemistry and Molecular Biology and The Graduate Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, MA 01003-4505, USA
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Green-Willms NS, Fox TD, Costanzo MC. Functional interactions between yeast mitochondrial ribosomes and mRNA 5' untranslated leaders. Mol Cell Biol 1998; 18:1826-34. [PMID: 9528754 PMCID: PMC121412 DOI: 10.1128/mcb.18.4.1826] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/1997] [Accepted: 12/22/1997] [Indexed: 02/07/2023] Open
Abstract
Translation of mitochondrial mRNAs in Saccharomyces cerevisiae depends on mRNA-specific translational activators that recognize the 5' untranslated leaders (5'-UTLs) of their target mRNAs. We have identified mutations in two new nuclear genes that suppress translation defects due to certain alterations in the 5'-UTLs of both the COX2 and COX3 mRNAs, indicating a general function in translational activation. One gene, MRP21, encodes a protein with a domain related to the bacterial ribosomal protein S21 and to unidentified proteins of several animals. The other gene, MRP51, encodes a novel protein whose only known homolog is encoded by an unidentified gene in S. kluyveri. Deletion of either MRP21 or MRP51 completely blocked mitochondrial gene expression. Submitochondrial fractionation showed that both Mrp21p and Mrp51p cosediment with the mitochondrial ribosomal small subunit. The suppressor mutations are missense substitutions, and those affecting Mrp21p alter the region homologous to E. coli S21, which is known to interact with mRNAs. Interactions of the suppressor mutations with leaky mitochondrial initiation codon mutations strongly suggest that the suppressors do not generally increase translational efficiency, since some alleles that strongly suppress 5'-UTL mutations fail to suppress initiation codon mutations. We propose that mitochondrial ribosomes themselves recognize a common feature of mRNA 5'-UTLs which, in conjunction with mRNA-specific translational activation, is required for organellar translation initiation.
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Affiliation(s)
- N S Green-Willms
- Section of Genetics and Development, Cornell University, Ithaca, New York 14853-2703, USA
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Zerges W, Girard-Bascou J, Rochaix JD. Translation of the chloroplast psbC mRNA is controlled by interactions between its 5' leader and the nuclear loci TBC1 and TBC3 in Chlamydomonas reinhardtii. Mol Cell Biol 1997; 17:3440-8. [PMID: 9154843 PMCID: PMC232197 DOI: 10.1128/mcb.17.6.3440] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Translation of the chloroplast psbC mRNA in Chlamydomonas reinhardtii has been shown previously to require interactions between its 5' untranslated region (5' UTR) and the functions encoded by two nuclear loci, which we name here TBC1 and TBC2. We show that a 97-nucleotide (nt) region located in the middle of the psbC 5' UTR is required for translation initiation. Unlike most procaryotic cis-acting translational control elements, this region has a translational activation function and is located 236 nt upstream from the GUG translation initiation codon. In vivo pulse-labeling of chloroplast-encoded proteins and analyses of the expression of chimeric reporter genes in vivo reveal that a mutation of a newly described locus, TBC3, restores translation from the psbC 5' UTR in the absence of either this cis-acting element or the wild-type trans-acting TBC1 function. These data demonstrate that sequences located in the middle of the psbC 5' UTR, TBC1, and TBC3 functionally interact to control the translation of the psbC mRNA.
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Affiliation(s)
- W Zerges
- Department of Molecular Biology, University of Geneva, Switzerland.
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40
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Fox TD. Translational control of endogenous and recoded nuclear genes in yeast mitochondria: regulation and membrane targeting. EXPERIENTIA 1996; 52:1130-5. [PMID: 8988256 DOI: 10.1007/bf01952112] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Mitochondrial gene expression in yeast, Saccharomyces cerevisiae, depends on translational activation of individual mRNAs by distinct proteins encoded in the nucleus. These unclearly coded mRNA-specific translational activators are bound to the inner membrane and function to mediate the interaction between mRNAs and mitochondrial ribosomes. This complex system, found to date only in organelles, appears to be an adaptation for targeting the synthesis of mitochondrially coded integral membrane proteins to the membrane. In addition, mRNA-specific translational activation is a rate-limiting step used to modulate expression of at least one mitochondrial gene in response to environmental conditions. Direct study of mitochondrial gene regulation and the targeting of mitochondrially coded proteins in vivo will now be possible using synthetic genes inserted into mtDNA that encode soluble reporter/passenger proteins.
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Affiliation(s)
- T D Fox
- Section of Genetics and Development, Cornell University, Ithaca, New York 14853-2703, USA.
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Costanzo MC, Fox TD. A point mutation in the 5'-untranslated leader that affects translational activation of the mitochondrial COX3 mRNA. Curr Genet 1995; 28:60-6. [PMID: 8536314 DOI: 10.1007/bf00311882] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The 613-base 5'-untranslated leader (5'-UTL) of the Saccharomyces cerevisiae mitochondrial COX3 mRNA contains the target of an mRNA-specific translational activator complex composed of at least three nuclearly encoded proteins. We have genetically mapped a collection of cox3 point mutations, using a set of defined COX3 deletions, and found one to be located in the region coding the 5'-UTL. The strain carrying this allele was specifically defective in translation of the COX3 mRNA. Nucleotide-sequence analysis showed that the allele was in fact a double mutation comprised of a single-base insertion in the 5'-UTL (T inserted between bases -428 and -427 with respect to the start of translation) and a G to A substitution at +3 that changed the ATG initiation codon to ATA. Both mutations were required to block translation completely. The effects of the ATG to ATA mutation alone (cox3-1) had previously been analyzed in this laboratory: it reduces, but does not eliminate, translation, causing a slow respiratory growth phenotype. The T insertion in the 5'-UTL had no detectable respiratory growth phenotype as a single mutation. However, the 5'-UTL insertion mutation enhanced the respiratory defective phenotype of missense mutations in pet54, one of the COX3-specific translational-activator genes. This phenotypic enhancement suggests that the -400 region of the 5'-UTL, where the mutation is located, is important for Pet54p-COX3 mRNA interaction.
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Affiliation(s)
- M C Costanzo
- Section of Genetics and Development, Cornell University, Ithaca, NY 14853-2703, USA
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42
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Wiesenberger G, Costanzo MC, Fox TD. Analysis of the Saccharomyces cerevisiae mitochondrial COX3 mRNA 5' untranslated leader: translational activation and mRNA processing. Mol Cell Biol 1995; 15:3291-300. [PMID: 7539105 PMCID: PMC230562 DOI: 10.1128/mcb.15.6.3291] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
We used transformation of yeast mitochondria and homologous gene replacement to study features of the 613-base COX3 mRNA 5' untranslated leader (5'-UTL) required for translational activation by the protein products of the nuclear genes PET54, PET122, and PET494 in vivo. Elimination of the single AUG triplet in the 5'-UTL had no detectable effect on expression, indicating that activator proteins do not work by allowing ribosomes to bypass that AUG. Deletion of the entire 5'-UTL completely prevented translation, suggesting that the activator proteins do not function by antagonizing any other negative element in the 5'-UTL. Removal of the 15 terminal bases from the 5' end of the 5'-UTL did not block activator-dependent translation. The largest internal deletion that did not interfere with translation removed 125 bases from the upstream portion of the leader. However, two large deletions that blocked translation could be reverted to activator-dependent expression by secondary changes in the remaining 5'-UTL sequences, indicating that the original deletions had not removed the translational activator target but only deformed it. Taken together, the deletion mutations and revertants define a region of 151 bases (between positions -480 and -330 relative to the start codon) containing sequences that are sufficient for translational activation when modified slightly. Suppression of the respiratory phenotypes of two 5'-UTL mutations by overexpression of PET54, PET122, and PET494 indicated functional interactions between the leader and the three activator proteins. The mature COX3 mRNA is cleaved from a precursor immediately downstream of the preceding tRNAVal in a fashion resembling mRNA processing in vertebrate mitochondria. Our results indicate that the site of this cleavage in Saccharomyces cerevisiae is determined solely by the position of the tRNA.
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Affiliation(s)
- G Wiesenberger
- Section of Genetics and Development, Cornell University, Ithaca, New York 14853-2703, USA
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43
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Mittelmeier TM, Dieckmann CL. In vivo analysis of sequences required for translation of cytochrome b transcripts in yeast mitochondria. Mol Cell Biol 1995; 15:780-9. [PMID: 7823946 PMCID: PMC231951 DOI: 10.1128/mcb.15.2.780] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Respiratory chain proteins encoded by the yeast mitochondrial genome are synthesized within the organelle. Mitochondrial mRNAs lack a 5' cap structure and contain long AU-rich 5' untranslated regions (UTRs) with many potential translational start sites and no apparent Shine-Dalgarno-like complementarity to the 15S mitochondrial rRNA. However, translation initiation requires specific interactions between the 5' UTRs of the mRNAs, mRNA-specific activators, and the ribosomes. In an initial step toward identifying potential binding sites for the mRNA-specific translational activators and the ribosomes, we have analyzed the effects of deletions in the 5' UTR of the mitochondrial COB gene on translation of COB transcripts in vivo. The deletions define two regions of the COB 5' UTR that are important for translation and indicate that sequence just 5' of the AUG is involved in selection of the correct start codon. Taken together, the data implicate specific regions of the 5' UTR of COB mRNA as possible targets for the mitochondrial translational machinery.
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Affiliation(s)
- T M Mittelmeier
- Department of Molecular and Cellular Biology, University of Arizona, Tucson 85721
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Abstract
All proteins encoded by mitochondrial DNA (mtDNA) are dependent on proteins encoded by nuclear genes for their synthesis and function. Recent developments in the identification of these genes and the elucidation of the roles their products play at various stages of mitochondrial gene expression are covered in this review, which focuses mainly on work with the yeast Saccharomyces cerevisiae. The high degree of evolutionary conservation of many cellular processes between this yeast and higher eukaryotes, the ease with which mitochondrial biogenesis can be manipulated both genetically and physiologically, and the fact that it will be the first organism for which a complete genomic sequence will be available within the next 2 to 3 years makes it the organism of choice for drawing up an inventory of all nuclear genes involved in mitochondrial biogenesis and for the identification of their counterparts in other organisms.
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Affiliation(s)
- L A Grivell
- Department of Molecular Cell Biology, University of Amsterdam, Netherlands
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45
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Affiliation(s)
- H J Pel
- Department of Molecular Cell Biology, University of Amsterdam, The Netherlands
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46
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Interactions among three proteins that specifically activate translation of the mitochondrial COX3 mRNA in Saccharomyces cerevisiae. Mol Cell Biol 1994. [PMID: 8289785 DOI: 10.1128/mcb.14.2.1045] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The PET54, PET122, and PET494 proteins, which are associated with the yeast inner mitochondrial membrane, specifically activate translation of the mitochondrially encoded COX3 mRNA. We used the two-hybrid system to test whether pairs of these proteins, when fused to either the GAL4 DNA-binding or transcriptional activating domain, can physically associate as measured by the expression of the GAL4-dependent reporter, lacZ. PET54 and PET122 interacted in this system, and an amino-terminally truncated PET494 fragment showed an interaction with PET54. We also detected functional interactions between PET54 and PET122 genetically: a pet54 missense substitution (Phe to Gly at position 244) that caused a severe respiratory defect was suppressed both by a missense substitution affecting PET122 (Gly to Val at position 211) and by overproduction of wild-type PET122. Both Gly and Ala, substituted at PET54 position 244, disrupted the two-hybrid interactions with PET122 and PET494. While Ala at PET54 position 244 caused only a modest respiratory phenotype alone, it caused a severe respiratory defect when combined with a cold-sensitive mitochondrial mutation affecting the COX3 mRNA 5' leader. This synthetic defect was suppressed by a missense substitution in PET122 and by overproduction of wild-type PET122, indicating functional interactions among PET54, PET122, and the mRNA. Taken together with previous work, these data suggest that a complex containing PET54, PET122, and PET494 mediates the interaction of the COX3 mRNA with mitochondrial ribosomes at the surface of the inner membrane.
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Brown NG, Costanzo MC, Fox TD. Interactions among three proteins that specifically activate translation of the mitochondrial COX3 mRNA in Saccharomyces cerevisiae. Mol Cell Biol 1994; 14:1045-53. [PMID: 8289785 PMCID: PMC358460 DOI: 10.1128/mcb.14.2.1045-1053.1994] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The PET54, PET122, and PET494 proteins, which are associated with the yeast inner mitochondrial membrane, specifically activate translation of the mitochondrially encoded COX3 mRNA. We used the two-hybrid system to test whether pairs of these proteins, when fused to either the GAL4 DNA-binding or transcriptional activating domain, can physically associate as measured by the expression of the GAL4-dependent reporter, lacZ. PET54 and PET122 interacted in this system, and an amino-terminally truncated PET494 fragment showed an interaction with PET54. We also detected functional interactions between PET54 and PET122 genetically: a pet54 missense substitution (Phe to Gly at position 244) that caused a severe respiratory defect was suppressed both by a missense substitution affecting PET122 (Gly to Val at position 211) and by overproduction of wild-type PET122. Both Gly and Ala, substituted at PET54 position 244, disrupted the two-hybrid interactions with PET122 and PET494. While Ala at PET54 position 244 caused only a modest respiratory phenotype alone, it caused a severe respiratory defect when combined with a cold-sensitive mitochondrial mutation affecting the COX3 mRNA 5' leader. This synthetic defect was suppressed by a missense substitution in PET122 and by overproduction of wild-type PET122, indicating functional interactions among PET54, PET122, and the mRNA. Taken together with previous work, these data suggest that a complex containing PET54, PET122, and PET494 mediates the interaction of the COX3 mRNA with mitochondrial ribosomes at the surface of the inner membrane.
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Affiliation(s)
- N G Brown
- Section of Genetics and Development, Cornell University, Ithaca, New York 14853-2703
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Mulero JJ, Fox TD. Alteration of the Saccharomyces cerevisiae COX2 mRNA 5'-untranslated leader by mitochondrial gene replacement and functional interaction with the translational activator protein PET111. Mol Biol Cell 1993; 4:1327-35. [PMID: 8167413 PMCID: PMC275768 DOI: 10.1091/mbc.4.12.1327] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The ability to replace wild-type mitochondrial DNA sequences in yeast with in vitro-generated mutations has been exploited to study the mechanism by which the nuclearly encoded PET111 protein specifically activates translation of the mitochondrially coded COX2 mRNA. We have generated three mutations in vitro that alter the COX2 mRNA 5'-untranslated leader (UTL) and introduced them into the mitochondrial genome, replacing the wild-type sequence. None of the mutations significantly affected the steady-state level of COX2 mRNA. Deletion of a single base at position -24 (relative to the translation initiation codon) in the 5'-UTL (cox2-11) reduced COX2 mRNA translation and respiratory growth, whereas insertion of four bases in place of the deleted base (cox2-12) and deletion of bases -30 to -2 (cox2-13) completely blocked both. Six spontaneous nuclear mutations were selected as suppressors of the single-base 5'-UTL deletion, cox2-11. One of these mapped to PET111 and was shown to be a missense mutation that changed residue 652 from Ala to Thr. This suppressor, PET111-20, failed to suppress the 29-base deletion, cox2-13, but very weakly suppressed the insertion mutation, cox2-12. PET111-20 also enhanced translation of a partially functional COX2 mRNA with a wild-type 5'-UTL but a mutant initiation codon. Although overexpression of the wild-type PET111 protein caused weak suppression of the single-base deletion, cox2-11, the PET111-20 suppressor mutation did not function simply by increasing the level of the protein. These results demonstrate an intimate functional interaction between the translational activator protein and the mRNA 5'-UTL and suggest that they may interact directly.
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Affiliation(s)
- J J Mulero
- Sections of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853-2703
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Elzinga SD, Bednarz AL, van Oosterum K, Dekker PJ, Grivell LA. Yeast mitochondrial NAD(+)-dependent isocitrate dehydrogenase is an RNA-binding protein. Nucleic Acids Res 1993; 21:5328-31. [PMID: 7505425 PMCID: PMC310566 DOI: 10.1093/nar/21.23.5328] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
We have previously described the characterisation of an abundant mitochondrial protein (p40) that binds specifically to 5'-untranslated leaders of mitochondrial mRNAs in yeast. p40 consists of two polypeptides with M(r) of 40 and 39 kDa. Limited sequence analysis of p40 identifies it as the Krebs cycle enzyme NAD(+)-dependent isocitrate dehydrogenase (Idh). Both enzyme and RNA-binding activities are specifically lost in cells containing disruptions in either IDH1 or IDH2, the nuclear genes encoding the two subunits of the enzyme, thus conclusively identifying p40 as Idh and showing that both activities are dependent on the simultaneous presence of both subunits. Although we still must ascertain whether and how either function of Idh is regulated and whether the two functions are compatible or mutually exclusive, this combination of dehydrogenase activity and RNA-binding in a single protein may be part of a general regulatory circuit linking the need for mitochondrial function to mitochondrial biogenesis.
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Affiliation(s)
- S D Elzinga
- Department of Molecular Cell-Biology, University of Amsterdam, The Netherlands
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50
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Suppression of a defect in the 5' untranslated leader of mitochondrial COX3 mRNA by a mutation affecting an mRNA-specific translational activator protein. Mol Cell Biol 1993. [PMID: 8393138 DOI: 10.1128/mcb.13.8.4806] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Translation of the Saccharomyces cerevisiae mitochondrial COX3 mRNA, encoding subunit III of cytochrome c oxidase, specifically requires the action of the nuclear gene products PET54, PET122, and PET494 at a site encoded in the 612-base 5' untranslated leader. To identify more precisely the site of action of the translational activators, we constructed two large deletions of the COX3 mRNA 5' untranslated leader. Both deletions blocked translation without affecting mRNA stability. However, one of the large deletions was able to revert to partial function by a small secondary deletion within the remaining 5' leader sequences. Translation of the resulting mutant (cox3-15) mRNA was still dependent on the nuclear-encoded specific activators but was cold sensitive. We selected revertants of this mitochondrial mutant at low temperature to identify genes encoding proteins that might interact with the COX3 mRNA 5' leader. One such revertant carried a missense mutation in the PET122 gene that was a strong and dominant suppressor of the cold-sensitive defect in the mRNA, indicating that the PET122 protein interacts functionally (possibly directly) with the COX3 mRNA 5' leader. The cox3-15 mutation was not suppressed by overproduction of the wild-type PET122 protein but was very weakly suppressed by overproduction of PET494 and slightly better suppressed by co-overproduction of PET494 and PET122.
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