1
|
Golik P. RNA processing and degradation mechanisms shaping the mitochondrial transcriptome of budding yeasts. IUBMB Life 2024; 76:38-52. [PMID: 37596708 DOI: 10.1002/iub.2779] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2023] [Accepted: 07/25/2023] [Indexed: 08/20/2023]
Abstract
Yeast mitochondrial genes are expressed as polycistronic transcription units that contain RNAs from different classes and show great evolutionary variability. The promoters are simple, and transcriptional control is rudimentary. Posttranscriptional mechanisms involving RNA maturation, stability, and degradation are thus the main force shaping the transcriptome and determining the expression levels of individual genes. Primary transcripts are fragmented by tRNA excision by RNase P and tRNase Z, additional processing events occur at the dodecamer site at the 3' end of protein-coding sequences. groups I and II introns are excised in a self-splicing reaction that is supported by protein splicing factors encoded by the nuclear genes, or by the introns themselves. The 3'-to-5' exoribonucleolytic complex called mtEXO is the main RNA degradation activity involved in RNA turnover and processing, supported by an auxiliary 5'-to-3' exoribonuclease Pet127p. tRNAs and, to a lesser extent, rRNAs undergo several different base modifications. This complex gene expression system relies on the coordinated action of mitochondrial and nuclear genes and undergoes rapid evolution, contributing to speciation events. Moving beyond the classical model yeast Saccharomyces cerevisiae to other budding yeasts should provide important insights into the coevolution of both genomes that constitute the eukaryotic genetic system.
Collapse
Affiliation(s)
- Pawel Golik
- Faculty of Biology, Institute of Genetics and Biotechnology, University of Warsaw, Warsaw, Poland
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| |
Collapse
|
2
|
Wang Y, Luo Y, Huang Y. Schizosaccharomyces pombe
Sls1 is primarily required for
cox1
mRNA translation. Yeast 2022; 39:521-534. [DOI: 10.1002/yea.3813] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Revised: 07/26/2022] [Accepted: 09/08/2022] [Indexed: 11/10/2022] Open
Affiliation(s)
- Yirong Wang
- Jiangsu Key Laboratory for Microbes and Functional Genomics, School of Life SciencesNanjing Normal University1 Wenyuan RoadNanjing210023China
| | - Ying Luo
- Jiangsu Key Laboratory for Microbes and Functional Genomics, School of Life SciencesNanjing Normal University1 Wenyuan RoadNanjing210023China
| | - Ying Huang
- Jiangsu Key Laboratory for Microbes and Functional Genomics, School of Life SciencesNanjing Normal University1 Wenyuan RoadNanjing210023China
| |
Collapse
|
3
|
Herbert CJ, Labarre-Mariotte S, Cornu D, Sophie C, Panozzo C, Michel T, Dujardin G, Bonnefoy N. Translational activators and mitoribosomal isoforms cooperate to mediate mRNA-specific translation in Schizosaccharomyces pombe mitochondria. Nucleic Acids Res 2021; 49:11145-11166. [PMID: 34634819 PMCID: PMC8565316 DOI: 10.1093/nar/gkab789] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 08/24/2021] [Accepted: 10/05/2021] [Indexed: 11/12/2022] Open
Abstract
Mitochondrial mRNAs encode key subunits of the oxidative phosphorylation complexes that produce energy for the cell. In Saccharomyces cerevisiae, mitochondrial translation is under the control of translational activators, specific to each mRNA. In Schizosaccharomyces pombe, which more closely resembles the human system by its mitochondrial DNA structure and physiology, most translational activators appear to be either lacking, or recruited for post-translational functions. By combining bioinformatics, genetic and biochemical approaches we identified two interacting factors, Cbp7 and Cbp8, controlling Cytb production in S. pombe. We show that their absence affects cytb mRNA stability and impairs the detection of the Cytb protein. We further identified two classes of Cbp7/Cbp8 partners and showed that they modulated Cytb or Cox1 synthesis. First, two isoforms of bS1m, a protein of the small mitoribosomal subunit, that appear mutually exclusive and confer translational specificity. Second, a complex of four proteins dedicated to Cox1 synthesis, which includes an RNA helicase that interacts with the mitochondrial ribosome. Our results suggest that S. pombe contains, in addition to complexes of translational activators, a heterogeneous population of mitochondrial ribosomes that could specifically modulate translation depending on the mRNA translated, in order to optimally balance the production of different respiratory complex subunits.
Collapse
Affiliation(s)
- Christopher J Herbert
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France
| | - Sylvie Labarre-Mariotte
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France
| | - David Cornu
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France
| | - Cyrielle Sophie
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France
| | - Cristina Panozzo
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France
| | - Thomas Michel
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France
| | - Geneviève Dujardin
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France
| | - Nathalie Bonnefoy
- Institute of Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France
| |
Collapse
|
4
|
Liu J, Li Y, Chen J, Wang Y, Zou M, Su R, Huang Y. The fission yeast Schizosaccharomyces pombe Mtf2 is required for mitochondrial cox1 gene expression. MICROBIOLOGY-SGM 2018; 164:400-409. [PMID: 29458562 DOI: 10.1099/mic.0.000602] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Mitochondrial gene expression is essential for adenosine triphosphate synthesis via oxidative phosphorylation, which is the universal energy currency of cells. Here, we report the identification and characterization of a homologue of Saccharomyces cerevisiae Mtf2 (also called Nam1) in Schizosaccharomyces pombe. The Δmtf2 mutant with the intron-containing mitochondrial DNA (mtDNA) exhibited impaired growth on a rich medium containing the non-fermentable carbon source glycerol, suggesting that mtf2 is involved in mitochondrial function. mtf2 deletion in a mitochondrial intron-containing background resulted in a barely detectable level of the cox1 mRNA and a reduction in the level of the cob1 mRNA, and severely impaired cox1 translation. In contrast, mtf2 deletion in a mitochondrial intron-less background did not affect the levels of cox1 and cob1 mRNAs. However, Cox1 synthesis could not be restored to the control level in the Δmtf2 mutant with intron-less mtDNA. Our results suggest that unlike its counterpart in S. cerevisiae which plays a general role in synthesis of mtDNA-encoded proteins, S. pombe Mtf2 primarily functions in cox1 translation and the effect of mtf2 deletion on splicing of introns in mtDNA is likely due to a deficiency in the synthesis of intron-encoded maturases.
Collapse
Affiliation(s)
- Jinyu Liu
- Jiangsu Key Laboratory for Microbes and Functional Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, PR China
| | - Yan Li
- Jiangsu Key Laboratory for Microbes and Functional Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, PR China
| | - Jie Chen
- Jiangsu Key Laboratory for Microbes and Functional Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, PR China
| | - Yirong Wang
- Jiangsu Key Laboratory for Microbes and Functional Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, PR China
| | - Mengting Zou
- Jiangsu Key Laboratory for Microbes and Functional Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, PR China
| | - Ruyue Su
- Jiangsu Key Laboratory for Microbes and Functional Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, PR China
| | - Ying Huang
- Jiangsu Key Laboratory for Microbes and Functional Genomics, School of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, PR China
| |
Collapse
|
5
|
Kruszewski J, Golik P. Pentatricopeptide Motifs in the N-Terminal Extension Domain of Yeast Mitochondrial RNA Polymerase Rpo41p Are Not Essential for Its Function. BIOCHEMISTRY. BIOKHIMIIA 2016; 81:1101-1110. [PMID: 27908235 DOI: 10.1134/s0006297916100084] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The core mitochondrial RNA polymerase is a single-subunit enzyme that in yeast Saccharomyces cerevisiae is encoded by the nuclear RPO41 gene. It is an evolutionary descendant of the bacteriophage RNA polymerases, but it includes an additional unconserved N-terminal extension (NTE) domain that is unique to the organellar enzymes. This domain mediates interactions between the polymerase and accessory regulatory factors, such as yeast Sls1p and Nam1p. Previous studies demonstrated that deletion of the entire NTE domain results only in a temperature-dependent respiratory deficiency. Several sequences related to the pentatricopeptide (PPR) motifs were identified in silico in Rpo41p, three of which are located in the NTE domain. PPR repeat proteins are a large family of organellar RNA-binding factors, mostly involved in posttranscriptional gene expression mechanisms. To study their function, we analyzed the phenotype of strains bearing Rpo41p variants where each of these motifs was deleted. We found that deletion of any of the three PPR motifs in the NTE domain does not affect respiratory growth at normal temperature, and it results in a moderate decrease in mtDNA stability. Steady-state levels of COX1 and COX2 mRNAs are also moderately affected. Only the deletion of the second motif results in a partial respiratory deficiency, manifested only at elevated temperature. Our results thus indicate that the PPR motifs do not play an essential role in the function of the NTE domain of the mitochondrial RNA polymerase.
Collapse
Affiliation(s)
- J Kruszewski
- University of Warsaw, Institute of Genetics and Biotechnology, Faculty of Biology, Warsaw, 02-106, Poland.
| | | |
Collapse
|
6
|
Yang X, Chang HR, Yin YW. Yeast Mitochondrial Transcription Factor Mtf1 Determines the Precision of Promoter-Directed Initiation of RNA Polymerase Rpo41. PLoS One 2015; 10:e0136879. [PMID: 26332125 PMCID: PMC4558008 DOI: 10.1371/journal.pone.0136879] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Accepted: 08/09/2015] [Indexed: 11/18/2022] Open
Abstract
Despite their clear T7-bacteriophage origin, mitochondrial RNA polymerases have evolved to require transcription factors. All mitochondrial polymerases contain an extra N-terminal domain that has no counterpart in the self-proficient phage enzyme, which is therefore hypothesized to interact with transcription factors. We studied a series of N-terminal deletion mutants of yeast mitochondrial RNA polymerase, Rpo41, and have found that the N-terminal region does not abolish the effects of Mtf1; rather it contributes directly to enzyme catalysis. Mtf1 can rescue the defective Rpo41 enzymes resulted from N-terminal domain deletions. Although Rpo41 appears to have retained all promoter recognition elements found in T7 RNAP, the elements are not independently functional, and Mtf1 is necessary and sufficient for holoenzyme promoter-directed transcription activity.
Collapse
Affiliation(s)
- Xu Yang
- Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, TX, 78712, United States of America
| | - Hae Ryung Chang
- Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, TX, 78712, United States of America
| | - Y. Whitney Yin
- Department of Pharmacology and Toxicology, Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, 77555, United States of America
- * E-mail:
| |
Collapse
|
7
|
Roloff GA, Henry MF. Mam33 promotes cytochrome c oxidase subunit I translation in Saccharomyces cerevisiae mitochondria. Mol Biol Cell 2015; 26:2885-94. [PMID: 26108620 PMCID: PMC4571327 DOI: 10.1091/mbc.e15-04-0222] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Accepted: 06/16/2015] [Indexed: 12/22/2022] Open
Abstract
Expression of genes encoded by the mitochondrial genome is dependent on gene-specific translational activators. Mam33, the yeast homologue of p32/gC1qR/C1QBP/HABP1, promotes the translation of Cox1, a core catalytic subunit of respiratory chain complex IV. Three mitochondrial DNA–encoded proteins, Cox1, Cox2, and Cox3, comprise the core of the cytochrome c oxidase complex. Gene-specific translational activators ensure that these respiratory chain subunits are synthesized at the correct location and in stoichiometric ratios to prevent unassembled protein products from generating free oxygen radicals. In the yeast Saccharomyces cerevisiae, the nuclear-encoded proteins Mss51 and Pet309 specifically activate mitochondrial translation of the largest subunit, Cox1. Here we report that Mam33 is a third COX1 translational activator in yeast mitochondria. Mam33 is required for cells to adapt efficiently from fermentation to respiration. In the absence of Mam33, Cox1 translation is impaired, and cells poorly adapt to respiratory conditions because they lack basal fermentative levels of Cox1.
Collapse
Affiliation(s)
- Gabrielle A Roloff
- Department of Molecular Biology, Rowan University School of Osteopathic Medicine, and Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084
| | - Michael F Henry
- Department of Molecular Biology, Rowan University School of Osteopathic Medicine, and Graduate School of Biomedical Sciences, Rowan University, Stratford, NJ 08084
| |
Collapse
|
8
|
Yang RF, Sun LH, Zhang R, Zhang Y, Luo YX, Zheng W, Zhang ZQ, Chen HZ, Liu DP. Suppression of Mic60 compromises mitochondrial transcription and oxidative phosphorylation. Sci Rep 2015; 5:7990. [PMID: 25612828 PMCID: PMC4303897 DOI: 10.1038/srep07990] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Accepted: 12/29/2014] [Indexed: 12/12/2022] Open
Abstract
Precise regulation of mtDNA transcription and oxidative phosphorylation (OXPHOS) is crucial for human health. As a component of mitochondrial contact site and cristae organizing system (MICOS), Mic60 plays a central role in mitochondrial morphology. However, it remains unclear whether Mic60 affects mitochondrial transcription. Here, we report that Mic60 interacts with mitochondrial transcription factors TFAM and TFB2M. Furthermore, we found that Mic60 knockdown compromises mitochondrial transcription and OXPHOS activities. Importantly, Mic60 deficiency decreased TFAM binding and mitochondrial RNA polymerase (POLRMT) recruitment to the mtDNA promoters. In addition, through mtDNA immunoprecipitation (mIP)-chromatin conformation capture (3C) assays, we found that Mic60 interacted with mtDNA and was involved in the architecture of mtDNA D-loop region. Taken together, our findings reveal a previously unrecognized important role of Mic60 in mtDNA transcription.
Collapse
Affiliation(s)
- Rui-Feng Yang
- State Key Laboratory of Medical Molecular Biology, Department of Biochemistry and Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences &Peking Union Medical College, Beijing 100005, P.R. China
| | - Li-Hong Sun
- State Key Laboratory of Medical Molecular Biology, Department of Biochemistry and Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences &Peking Union Medical College, Beijing 100005, P.R. China
| | - Ran Zhang
- State Key Laboratory of Medical Molecular Biology, Department of Biochemistry and Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences &Peking Union Medical College, Beijing 100005, P.R. China
| | - Yuan Zhang
- State Key Laboratory of Medical Molecular Biology, Department of Biochemistry and Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences &Peking Union Medical College, Beijing 100005, P.R. China
| | - Yu-Xuan Luo
- State Key Laboratory of Medical Molecular Biology, Department of Biochemistry and Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences &Peking Union Medical College, Beijing 100005, P.R. China
| | - Wei Zheng
- State Key Laboratory of Medical Molecular Biology, Department of Biochemistry and Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences &Peking Union Medical College, Beijing 100005, P.R. China
| | - Zhu-Qin Zhang
- State Key Laboratory of Medical Molecular Biology, Department of Biochemistry and Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences &Peking Union Medical College, Beijing 100005, P.R. China
| | - Hou-Zao Chen
- State Key Laboratory of Medical Molecular Biology, Department of Biochemistry and Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences &Peking Union Medical College, Beijing 100005, P.R. China
| | - De-Pei Liu
- State Key Laboratory of Medical Molecular Biology, Department of Biochemistry and Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences &Peking Union Medical College, Beijing 100005, P.R. China
| |
Collapse
|
9
|
Ostojić J, Glatigny A, Herbert CJ, Dujardin G, Bonnefoy N. Does the study of genetic interactions help predict the function of mitochondrial proteins in Saccharomyces cerevisiae? Biochimie 2013; 100:27-37. [PMID: 24262604 DOI: 10.1016/j.biochi.2013.11.004] [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: 09/20/2013] [Accepted: 11/06/2013] [Indexed: 10/26/2022]
Abstract
Mitochondria are complex organelles of eukaryotic cells that contain their own genome, encoding key subunits of the respiratory complexes. The successive steps of mitochondrial gene expression are intimately linked, and are under the control of a large number of nuclear genes encoding factors that are imported into mitochondria. Investigating the relationships between these genes and their interaction networks, and whether they reveal direct or indirect partners, can shed light on their role in mitochondrial biogenesis, as well as identify new actors in this process. These studies, mainly developed in yeasts, are significant because mammalian equivalents of such yeast genes are candidate genes in mitochondrial pathologies. In practice, studies of physical, chemical and genetic interactions can be undertaken. The search for genetic interactions, either aggravating or alleviating the phenotype of the starting mutants, has proved to be particularly powerful in yeast since even subtle changes in respiratory phenotypes can be screened in a very efficient way. In addition, several high throughput genetic approaches have recently been developed. In this review we analyze the genetic network of three genes involved in different steps of mitochondrial gene expression, from the transcription and translation of mitochondrial RNAs to the insertion of newly synthesized proteins into the inner mitochondrial membrane, and we examine their relevance to our understanding of mitochondrial biogenesis. We find that these genetic interactions are seldom redundant with physical interactions, and thus bring a considerable amount of original and significant information as well as open new areas of research.
Collapse
Affiliation(s)
- Jelena Ostojić
- Centre de Génétique Moléculaire, CNRS UPR3404 Associated to the University Paris XI-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
| | - Annie Glatigny
- Centre de Génétique Moléculaire, CNRS UPR3404 Associated to the University Paris XI-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
| | - Christopher J Herbert
- Centre de Génétique Moléculaire, CNRS UPR3404 Associated to the University Paris XI-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
| | - Geneviève Dujardin
- Centre de Génétique Moléculaire, CNRS UPR3404 Associated to the University Paris XI-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France
| | - Nathalie Bonnefoy
- Centre de Génétique Moléculaire, CNRS UPR3404 Associated to the University Paris XI-Sud, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France.
| |
Collapse
|
10
|
Herbert CJ, Golik P, Bonnefoy N. Yeast PPR proteins, watchdogs of mitochondrial gene expression. RNA Biol 2013; 10:1477-94. [PMID: 24184848 DOI: 10.4161/rna.25392] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
PPR proteins are a family of ubiquitous RNA-binding factors, found in all the Eukaryotic lineages, and are particularly numerous in higher plants. According to recent bioinformatic analyses, yeast genomes encode from 10 (in S. pombe) to 15 (in S. cerevisiae) PPR proteins. All of these proteins are mitochondrial and very often interact with the mitochondrial membrane. Apart from the general factors, RNA polymerase and RNase P, most yeast PPR proteins are involved in the stability and/or translation of mitochondrially encoded RNAs. At present, some information concerning the target RNA(s) of most of these proteins is available, the next challenge will be to refine our understanding of the function of the proteins and to resolve the yeast PPR-RNA-binding code, which might differ significantly from the plant PPR code.
Collapse
Affiliation(s)
- Christopher J Herbert
- Centre de Génétique Moléculaire du CNRS; UPR3404; FRC3115; Gif-sur-Yvette; Paris, France
| | - Pawel Golik
- Department of Genetics and Biotechnology; Faculty of Biology; University of Warsaw; Pawinskiego 5A; Warsaw, Poland
| | - Nathalie Bonnefoy
- Centre de Génétique Moléculaire du CNRS; UPR3404; FRC3115; Gif-sur-Yvette; Paris, France
| |
Collapse
|
11
|
Abstract
The mitochondrion is arguably the most complex organelle in the budding yeast cell cytoplasm. It is essential for viability as well as respiratory growth. Its innermost aqueous compartment, the matrix, is bounded by the highly structured inner membrane, which in turn is bounded by the intermembrane space and the outer membrane. Approximately 1000 proteins are present in these organelles, of which eight major constituents are coded and synthesized in the matrix. The import of mitochondrial proteins synthesized in the cytoplasm, and their direction to the correct soluble compartments, correct membranes, and correct membrane surfaces/topologies, involves multiple pathways and macromolecular machines. The targeting of some, but not all, cytoplasmically synthesized mitochondrial proteins begins with translation of messenger RNAs localized to the organelle. Most proteins then pass through the translocase of the outer membrane to the intermembrane space, where divergent pathways sort them to the outer membrane, inner membrane, and matrix or trap them in the intermembrane space. Roughly 25% of mitochondrial proteins participate in maintenance or expression of the organellar genome at the inner surface of the inner membrane, providing 7 membrane proteins whose synthesis nucleates the assembly of three respiratory complexes.
Collapse
|
12
|
Surovtseva YV, Shadel GS. Transcription-independent role for human mitochondrial RNA polymerase in mitochondrial ribosome biogenesis. Nucleic Acids Res 2013; 41:2479-88. [PMID: 23303773 PMCID: PMC3575816 DOI: 10.1093/nar/gks1447] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Revised: 12/07/2012] [Accepted: 12/12/2012] [Indexed: 12/05/2022] Open
Abstract
Human mitochondrial RNA polymerase, POLRMT, is required for mitochondrial DNA (mtDNA) transcription and forms initiation complexes with human mitochondrial transcription factor B2 (h-mtTFB2). However, POLRMT also interacts with the paralogue of h-mtTFB2, h-mtTFB1, which is a 12S ribosomal RNA methyltransferase required for small (28S) mitochondrial ribosome subunit assembly. Herein, we show that POLRMT associates with h-mtTFB1 in 28S mitochondrial ribosome complexes that are stable in the absence of mitochondrial transcription and distinct from transcription complexes containing POLRMT and h-mtTFB2. Overexpression of POLRMT in HeLa cells increases 12S rRNA methylation by h-mtTFB1 and reduces the steady-state levels of mtDNA-encoded proteins and respiration, apparently because of a decrease in fully assembled 55S mitochondrial ribosomes. We propose that POLRMT interacts directly with h-mtTFB1 in 28S mitochondrial ribosomes to augment its 12S rRNA methyltransferase activity, and that together they provide a checkpoint for proper 28S and 55S mitochondrial ribosome assembly. Thus, POLRMT is multi-functional, forming distinct protein complexes that regulate different steps in mitochondrial gene expression, at least one of which does not involve transcription per se. The significance of these results is discussed with regard to the mechanism and regulation of human mitochondrial gene expression and the potential multi-functionality of RNA polymerases in general.
Collapse
Affiliation(s)
- Yulia V. Surovtseva
- Department of Pathology, Yale University School of Medicine, New Haven, CT 06520, USA and Department of Genetics, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Gerald S. Shadel
- Department of Pathology, Yale University School of Medicine, New Haven, CT 06520, USA and Department of Genetics, Yale University School of Medicine, New Haven, CT 06520, USA
| |
Collapse
|
13
|
Mitochondrial ribosomal protein L12 selectively associates with human mitochondrial RNA polymerase to activate transcription. Proc Natl Acad Sci U S A 2011; 108:17921-6. [PMID: 22003127 DOI: 10.1073/pnas.1108852108] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Basal transcription of human mitochondrial DNA (mtDNA) in vitro requires the single-subunit, bacteriophage-related RNA polymerase, POLRMT, and transcription factor h-mtTFB2. This two-component system is activated differentially at mtDNA promoters by human mitochondrial transcription factor A (h-mtTFA). Mitochondrial ribosomal protein L7/L12 (MRPL12) binds directly to POLRMT, but whether it does so in the context of the ribosome or as a "free" protein in the matrix is unknown. Furthermore, existing evidence that MRPL12 activates mitochondrial transcription derives from overexpression studies in cultured cells and transcription experiments using crude mitochondrial lysates, precluding direct effects of MRPL12 on transcription to be assigned. Here, we report that depletion of MRPL12 from HeLa cells by shRNA results in decreased steady-state levels of mitochondrial transcripts, which are not accounted for by changes in RNA stability. We also show that a significant "free" pool of MRPL12 exists in human mitochondria not associated with ribosomes. "Free" MRPL12 binds selectively to POLRMT in vivo in a complex distinct from those containing h-mtTFB2. Finally, using a fully recombinant mitochondrial transcription system, we demonstrate that MRPL12 stimulates promoter-dependent and promoter-independent transcription directly in vitro. Based on these results, we propose that, when not associated with ribosomes, MRPL12 has a second function in transcription, perhaps acting to facilitate the transition from initiation to elongation. We speculate that this is one mechanism to coordinate mitochondrial ribosome biogenesis and transcription in human mitochondria, where transcription of rRNAs from the mtDNA presumably needs to be adjusted in accordance with the rate of import and assembly of the nucleus-encoded MRPs into ribosomes.
Collapse
|
14
|
Evolution of the mitochondrial fusion-fission cycle and its role in aging. Proc Natl Acad Sci U S A 2011; 108:10237-42. [PMID: 21646529 DOI: 10.1073/pnas.1101604108] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Mitochondria are organelles of eukaryotic cells that contain their own genetic material and evolved from prokaryotic ancestors some 2 billion years ago. They are the main source of the cell's energy supply and are involved in such important processes as apoptosis, mitochondrial diseases, and aging. During recent years it also became apparent that mitochondria display a complex dynamical behavior of fission and fusion, the function of which is as yet unknown. In this paper we develop a concise theory that explains why fusion and fission have evolved, how these processes are related to the accumulation of mitochondrial mutants during aging, why the mitochondrial DNA has to be located close to the respiration complexes where most radicals are generated, and what selection pressures shaped the slightly different structure of animal and plant mitochondria. We believe that this "organelle control" theory will help in understanding key processes involved in the evolution of the mitochondrial genome and the aging process.
Collapse
|
15
|
Buschlen S, Amillet JM, Guiard B, Fournier A, Marcireau C, Bolotin-Fukuhara M. The S. Cerevisiae HAP complex, a key regulator of mitochondrial function, coordinates nuclear and mitochondrial gene expression. Comp Funct Genomics 2010; 4:37-46. [PMID: 18629096 PMCID: PMC2447382 DOI: 10.1002/cfg.254] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2002] [Accepted: 12/04/2002] [Indexed: 12/05/2022] Open
Abstract
We have compared Saccharomyces cerevisiae global gene expression in wild-type and mutants (Δhap2 and Δhap4) of the HAP transcriptional complex, which has been shown to be necessary for growth on respiratory substrates. Several hundred ORFs
are under positive or negative control of this complex and we analyse here in detail
the effect of HAP on mitochondria. We found that most of the genes upregulated
in the wild-type strain were involved in organelle functions, but practically none
of the downregulated ones. Nuclear genes encoding the different subunits of the
respiratory chain complexes figure in the genes more expressed in the wild-type than
in the mutants, as expected, but in this group we also found key components of
the mitochondrial translation apparatus. This control of mitochondrial translation
may be one of the means of coordinating mitochondrial and nuclear gene expression
in elaborating the respiratory chain. In addition, HAP controls the nuclear genes
involved in several other mitochondrial processes (import, mitochondrial division)
that define the metabolic state of the cell, but not mitochondrial DNA replication and
transcription. In most cases, a putative CCAAT-binding site is present upstream of the
ORF, while in others no such sites are present, suggesting the control to be indirect.
The large number of genes regulated by the HAP complex, as well as the fact that HAP
also regulates some putative transcriptional activators of unknown function, place this
complex at a hierarchically high position in the global transcriptional regulation of
the cell.
Collapse
Affiliation(s)
- S Buschlen
- Laboratoire de Génétique Moléculaire, IGM, Batiment 400. Université Paris Sud, 91405 Orsay Cedex, France
| | | | | | | | | | | |
Collapse
|
16
|
Lipinski KA, Kaniak-Golik A, Golik P. Maintenance and expression of the S. cerevisiae mitochondrial genome--from genetics to evolution and systems biology. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2010; 1797:1086-98. [PMID: 20056105 DOI: 10.1016/j.bbabio.2009.12.019] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2009] [Revised: 12/18/2009] [Accepted: 12/24/2009] [Indexed: 10/20/2022]
Abstract
As a legacy of their endosymbiotic eubacterial origin, mitochondria possess a residual genome, encoding only a few proteins and dependent on a variety of factors encoded by the nuclear genome for its maintenance and expression. As a facultative anaerobe with well understood genetics and molecular biology, Saccharomyces cerevisiae is the model system of choice for studying nucleo-mitochondrial genetic interactions. Maintenance of the mitochondrial genome is controlled by a set of nuclear-coded factors forming intricately interconnected circuits responsible for replication, recombination, repair and transmission to buds. Expression of the yeast mitochondrial genome is regulated mostly at the post-transcriptional level, and involves many general and gene-specific factors regulating splicing, RNA processing and stability and translation. A very interesting aspect of the yeast mitochondrial system is the relationship between genome maintenance and gene expression. Deletions of genes involved in many different aspects of mitochondrial gene expression, notably translation, result in an irreversible loss of functional mtDNA. The mitochondrial genetic system viewed from the systems biology perspective is therefore very fragile and lacks robustness compared to the remaining systems of the cell. This lack of robustness could be a legacy of the reductive evolution of the mitochondrial genome, but explanations involving selective advantages of increased evolvability have also been postulated.
Collapse
Affiliation(s)
- Kamil A Lipinski
- Institute of Genetics and Biotechnology, Faculty of Biology, University of Warsaw, Pawinskiego 5A, 02-106, Warsaw, Poland
| | | | | |
Collapse
|
17
|
Markov DA, Savkina M, Anikin M, Del Campo M, Ecker K, Lambowitz AM, De Gnore JP, McAllister WT. Identification of proteins associated with the yeast mitochondrial RNA polymerase by tandem affinity purification. Yeast 2009; 26:423-40. [PMID: 19536766 PMCID: PMC2896726 DOI: 10.1002/yea.1672] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The abundance of mitochondrial (mt) transcripts varies under different conditions, and is thought to depend upon rates of transcription initiation, transcription termination/attenuation and RNA processing/degradation. The requirement to maintain the balance between RNA synthesis and processing may involve coordination between these processes; however, little is known about factors that regulate the activity of mtRNA polymerase (mtRNAP). Recent attempts to identify mtRNAP–protein interactions in yeast by means of a generalized tandem affinity purification (TAP) protocol were not successful, most likely because they involved a C-terminal mtRNAP–TAP fusion (which is incompatible with mtRNAP function) and because of the use of whole-cell solubilization protocols that did not preserve the integrity of mt protein complexes. Based upon the structure of T7 RNAP (to which mtRNAPs show high sequence similarity), we identified positions in yeast mtRNAP that allow insertion of a small affinity tag, confirmed the mature N-terminus, constructed a functional N-terminal TAP–mtRNAP fusion, pulled down associated proteins, and identified them by LC–MS–MS. Among the proteins found in the pull-down were a DEAD-box protein (Mss116p) and an RNA-binding protein (Pet127p). Previous genetic experiments suggested a role for these proteins in linking transcription and RNA degradation, in that a defect in the mt degradadosome could be suppressed by overexpression of either of these proteins or, independently, by mutations in either mtRNAP or its initiation factor Mtf1p. Further, we found that Mss116p inhibits transcription by mtRNAP in vitro in a steady-state reaction. Our results support the hypothesis that Mss116p and Pet127p are involved in modulation of mtRNAP activity. Copyright © 2009 John Wiley & Sons, Ltd.
Collapse
Affiliation(s)
- Dmitriy A Markov
- Departments of Cell Biology, University of Medicine and Dentistry of New Jersey, Stratford, USA.
| | | | | | | | | | | | | | | |
Collapse
|
18
|
Miyakawa I, Okamuro A, Kinsky S, Visacka K, Tomaska L, Nosek J. Mitochondrial nucleoids from the yeast Candida parapsilosis: expansion of the repertoire of proteins associated with mitochondrial DNA. MICROBIOLOGY-SGM 2009; 155:1558-1568. [PMID: 19383705 DOI: 10.1099/mic.0.027474-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Molecules of mitochondrial DNA (mtDNA) are packed into nucleic acid-protein complexes termed mitochondrial nucleoids (mt-nucleoids). In this study, we analysed mt-nucleoids of the yeast Candida parapsilosis, which harbours a linear form of the mitochondrial genome. To identify conserved as well as specific features of mt-nucleoids in this species, we employed two strategies for analysis of their components. First, we investigated the protein composition of mt-nucleoids isolated from C. parapsilosis mitochondria, determined N-terminal amino acid sequences of 14 proteins associated with the mt-nucleoids and identified corresponding genes. Next, we complemented the list of mt-nucleoid components with additional candidates identified in the complete genome sequence of C. parapsilosis as homologues of Saccharomyces cerevisiae mt-nucleoid proteins. Our approach revealed several known mt-nucleoid proteins as well as additional components that expand the repertoire of proteins associated with these cytological structures. In particular, we identified and purified the protein Gcf1, which is abundant in the mt-nucleoids and exhibits structural features in common with the mtDNA packaging protein Abf2 from S. cerevisiae. We demonstrate that Gcf1p co-localizes with mtDNA, has DNA-binding activity in vitro, and is able to stabilize mtDNA in the S. cerevisiae Deltaabf2 mutant, all of which points to a role in the maintenance of the C. parapsilosis mitochondrial genome. Importantly, in contrast to Abf2p, in silico analysis of Gcf1p predicted the presence of a coiled-coil domain and a single high-mobility group (HMG) box, suggesting that it represents a novel type of mitochondrial HMG protein.
Collapse
Affiliation(s)
- Isamu Miyakawa
- Department of Physics, Biology, and Informatics, Faculty of Science, Yamaguchi University, Yamaguchi 753-8512, Japan
| | - Akira Okamuro
- Department of Physics, Biology, and Informatics, Faculty of Science, Yamaguchi University, Yamaguchi 753-8512, Japan
| | - Slavomir Kinsky
- Departments of Biochemistry and Genetics, Faculty of Natural Sciences, Comenius University, 842 15 Bratislava, Slovakia
| | - Katarina Visacka
- Departments of Biochemistry and Genetics, Faculty of Natural Sciences, Comenius University, 842 15 Bratislava, Slovakia
| | - Lubomir Tomaska
- Departments of Biochemistry and Genetics, Faculty of Natural Sciences, Comenius University, 842 15 Bratislava, Slovakia
| | - Jozef Nosek
- Departments of Biochemistry and Genetics, Faculty of Natural Sciences, Comenius University, 842 15 Bratislava, Slovakia
| |
Collapse
|
19
|
Clay Montier LL, Deng JJ, Bai Y. Number matters: control of mammalian mitochondrial DNA copy number. J Genet Genomics 2009; 36:125-31. [PMID: 19302968 PMCID: PMC4706993 DOI: 10.1016/s1673-8527(08)60099-5] [Citation(s) in RCA: 378] [Impact Index Per Article: 25.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2008] [Revised: 01/13/2009] [Accepted: 01/19/2009] [Indexed: 12/15/2022]
Abstract
Regulation of mitochondrial biogenesis is essential for proper cellular functioning. Mitochondrial DNA (mtDNA) depletion and the resulting mitochondrial malfunction have been implicated in cancer, neurodegeneration, diabetes, aging, and many other human diseases. Although it is known that the dynamics of the mammalian mitochondrial genome are not linked with that of the nuclear genome, very little is known about the mechanism of mtDNA propagation. Nevertheless, our understanding of the mode of mtDNA replication has advanced in recent years, though not without some controversies. This review summarizes our current knowledge of mtDNA copy number control in mammalian cells, while focusing on both mtDNA replication and turnover. Although mtDNA copy number is seemingly in excess, we reason that mtDNA copy number control is an important aspect of mitochondrial genetics and biogenesis and is essential for normal cellular function.
Collapse
Affiliation(s)
- Laura L Clay Montier
- Department of Cellular and Structural Biology, The Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
| | | | | |
Collapse
|
20
|
Kucejova B, Li L, Wang X, Giannattasio S, Chen XJ. Pleiotropic effects of the yeast Sal1 and Aac2 carriers on mitochondrial function via an activity distinct from adenine nucleotide transport. Mol Genet Genomics 2008; 280:25-39. [PMID: 18431598 PMCID: PMC2749980 DOI: 10.1007/s00438-008-0342-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2007] [Accepted: 04/03/2008] [Indexed: 11/25/2022]
Abstract
In Saccharomyces cerevisiae, SAL1 encodes a Ca2+ -binding mitochondrial carrier. Disruption of SAL1 is synthetically lethal with the loss of a specific function associated with the Aac2 isoform of the ATP/ADP translocase. This novel activity of Aac2 is defined as the V function (for Viability of aac2 sal1 double mutant), which is independent of the ATP/ADP exchange activity required for respiratory growth (the R function). We found that co-inactivation of SAL1 and AAC2 leads to defects in mitochondrial translation and mitochondrial DNA (mtDNA) maintenance. Additionally, sal1Delta exacerbates the respiratory deficiency and mtDNA instability of ggc1Delta, shy1Delta and mtg1Delta mutants, which are known to reduce mitochondrial protein synthesis or protein complex assembly. The V function is complemented by the human Short Ca2+ -binding Mitochondrial Carrier (SCaMC) protein, SCaMC-2, a putative ATP-Mg/Pi exchangers on the inner membrane. However, mitochondria lacking both Sal1p and Aac2p are not depleted of adenine nucleotides. The Aac2R252I and Aac2R253I variants mutated at the R252-254 triplet critical for nucleotide transport retain the V function. Likewise, Sal1p remains functionally active when the R479I and R481I mutations were introduced into the structurally equivalent R479-T480-R481 motif. Finally, we found that the naturally occurring V-R+ Aac1 isoform of adenine nucleotide translocase partially gains the V function at the expense of the R function by introducing the mutations P89L and A96 V. Thus, our data support the view that the V function is independent of adenine nucleotide transport associated with Sal1p and Aac2p and this evolutionarily conserved activity affects multiple processes in mitochondria.
Collapse
Affiliation(s)
- Blanka Kucejova
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9148,USA
| | - Li Li
- Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, NY 13210, USA
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9148,USA
| | - Xiaowen Wang
- Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, NY 13210, USA
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9148,USA
| | | | - Xin Jie Chen
- Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, NY 13210, USA
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9148,USA
| |
Collapse
|
21
|
Shadel GS. Expression and maintenance of mitochondrial DNA: new insights into human disease pathology. THE AMERICAN JOURNAL OF PATHOLOGY 2008; 172:1445-56. [PMID: 18458094 DOI: 10.2353/ajpath.2008.071163] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Mitochondria are central players in cellular energy metabolism and, consequently, defects in their function result in many characterized metabolic diseases. Critical for their function is mitochondrial DNA (mtDNA), which encodes subunits of the oxidative phosphorylation complexes essential for cellular respiration and ATP production. Expression, replication, and maintenance of mtDNA require factors encoded by nuclear genes. These include not only the primary machinery involved (eg, transcription and replication components) but also those in signaling pathways that mediate or sense alterations in mitochondrial function in accord with changing cellular needs or environmental conditions. Mutations in these contribute to human disease pathology by mechanisms that are being revealed at an unprecedented rate. As I will discuss herein, the basic protein machinery required for transcription initiation in human mitochondria has been elucidated after the discovery of two multifunctional mitochondrial transcription factors, h-mtTFB1 and h-mtTFB2, that are also rRNA methyltransferases. In addition, involvement of the ataxia-telangiectasia mutated (ATM) and target of rapamycin (TOR) signaling pathways in regulating mitochondrial homeostasis and gene expression has also recently been uncovered. These advancements embody the current mitochondrial research landscape, which can be described as exploding with discoveries of previously unanticipated roles for mitochondria in human disease and aging.
Collapse
Affiliation(s)
- Gerald S Shadel
- Departments of Pathology and Genetics, Yale University School of Medicine, 310 Cedar St., P.O. Box 208023, New Haven, CT 06520-8023.
| |
Collapse
|
22
|
Bogenhagen DF, Rousseau D, Burke S. The layered structure of human mitochondrial DNA nucleoids. J Biol Chem 2007; 283:3665-3675. [PMID: 18063578 DOI: 10.1074/jbc.m708444200] [Citation(s) in RCA: 316] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mitochondrial DNA (mtDNA) occurs in cells in nucleoids containing several copies of the genome. Previous studies have identified proteins associated with these large DNA structures when they are biochemically purified by sedimentation and immunoaffinity chromatography. In this study, formaldehyde cross-linking was performed to determine which nucleoid proteins are in close contact with the mtDNA. A set of core nucleoid proteins is found in both native and cross-linked nucleoids, including 13 proteins with known roles in mtDNA transactions. Several other metabolic proteins and chaperones identified in native nucleoids, including ATAD3, were not observed to cross-link to mtDNA. Additional immunofluorescence and protease susceptibility studies showed that an N-terminal domain of ATAD3 previously proposed to bind to the mtDNA D-loop is directed away from the mitochondrial matrix, so it is unlikely to interact with mtDNA in vivo. These results are discussed in relation to a model for a layered structure of mtDNA nucleoids in which replication and transcription occur in the central core, whereas translation and complex assembly may occur in the peripheral region.
Collapse
Affiliation(s)
- Daniel F Bogenhagen
- Department of Pharmacological Sciences, State University of New York at Stony Brook, Stony Brook, New York 11794-8651.
| | - Denis Rousseau
- Laboratoire Biochimie et Biophysique des Systèmes Intégrés p438B, Institut de Recherches en Technologies et Sciences pour le Vivant, UMR5092 CNRS-UJF-CEA-Grenoble, 17 Rue des Martyrs, 38054 Grenoble Cedex 09, France
| | - Stephanie Burke
- Department of Pharmacological Sciences, State University of New York at Stony Brook, Stony Brook, New York 11794-8651
| |
Collapse
|
23
|
Malecki M, Jedrzejczak R, Stepien PP, Golik P. In vitro reconstitution and characterization of the yeast mitochondrial degradosome complex unravels tight functional interdependence. J Mol Biol 2007; 372:23-36. [PMID: 17658549 DOI: 10.1016/j.jmb.2007.06.074] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2007] [Revised: 06/13/2007] [Accepted: 06/26/2007] [Indexed: 11/23/2022]
Abstract
The mitochondrial degradosome (mtEXO), the main RNA-degrading complex of yeast mitochondria, is composed of two subunits: an exoribonuclease encoded by the DSS1 gene and an RNA helicase encoded by the SUV3 gene. We expressed both subunits of the yeast mitochondrial degradosome in Escherichia coli, reconstituted the complex in vitro and analyzed the RNase, ATPase and helicase activities of the two subunits separately and in complex. The results reveal a very strong functional interdependence. For every enzymatic activity, we observed significant changes when the relevant protein was present in the complex, compared to the activity measured for the protein alone. The ATPase activity of Suv3p is stimulated by RNA and its background activity in the absence of RNA is reduced greatly when the protein is in the complex with Dss1p. The Suv3 protein alone does not display RNA-unwinding activity and the 3' to 5' directional helicase activity requiring a free 3' single-stranded substrate becomes apparent only when Suv3p is in complex with Dss1p. The Dss1 protein alone does have some basal exoribonuclease activity, which is not ATP-dependent, but in the presence of Suv3p the activity of the entire complex is enhanced greatly and is entirely ATP-dependent, with no residual activity observed in the absence of ATP. Such absolute ATP-dependence is unique among known exoribonuclease complexes. On the basis of these results, we propose a model in which the Suv3p RNA helicase acts as a molecular motor feeding the substrate to the catalytic centre of the RNase subunit.
Collapse
Affiliation(s)
- Michal Malecki
- Department of Genetics and Biotechnology, University of Warsaw, Pawinskiego 5A, 02-106, Warsaw, Poland
| | | | | | | |
Collapse
|
24
|
Wang Z, Cotney J, Shadel GS. Human mitochondrial ribosomal protein MRPL12 interacts directly with mitochondrial RNA polymerase to modulate mitochondrial gene expression. J Biol Chem 2007; 282:12610-8. [PMID: 17337445 PMCID: PMC2606046 DOI: 10.1074/jbc.m700461200] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The core human mitochondrial transcription machinery comprises a single subunit bacteriophage-related RNA polymerase, POLRMT, the high mobility group box DNA-binding protein h-mtTFA/TFAM, and two transcriptional co-activator proteins, h-mtTFB1 and h-mtTFB2 that also have rRNA methyltransferase activity. Recapitulation of specific initiation of transcription in vitro can be achieved by a complex of POL-RMT, h-mtTFA, and either h-mtTFB1 or h-mtTFB2. However, the nature of mitochondrial transcription complexes in vivo and the potential involvement of additional proteins in the transcription process in human mitochondria have not been extensively investigated. In Saccharomyces cerevisiae, transcription and translation are physically coupled via the formation of a multiprotein complex nucleated by the binding of Nam1p to the amino-terminal domain of mtRNA polymerase (Rpo41p). This model system paradigm led us to search for proteins that interact with POLRMT to regulate mitochondrial gene expression in humans. Using an affinity capture strategy to identify POL-RMT-binding proteins, we identified mitochondrial ribosomal protein L7/L12 (MRPL12) as a protein in HeLa mitochondrial extracts that interacts specifically with POLRMT in vitro. Purified recombinant MRPL12 binds to POLRMT and stimulates mitochondrial transcription activity in vitro, demonstrating that this interaction is both direct and functional. Finally, from HeLa cells that overexpress FLAG epitope-tagged MRPL12, increased steady-state levels of mtDNA-encoded transcripts are observed and MRPL12-POLRMT complexes can be co-immunoprecipitated, providing strong evidence that this interaction enhances mitochondrial transcription or RNA stability in vivo. We speculate that the MRPL12 interaction with POLRMT is likely part of a novel regulatory mechanism that coordinates mitochondrial transcription with translation and/or ribosome biogenesis during human mitochondrial gene expression.
Collapse
Affiliation(s)
- Zhibo Wang
- Department of Pathology, Yale University School of Medicine, New Haven, Connecticut 06520-8023
| | - Justin Cotney
- Department of Pathology, Yale University School of Medicine, New Haven, Connecticut 06520-8023
- Graduate Program in Genetics and Molecular Biology, Emory University School of Medicine, Atlanta, Georgia 30322-3050
| | - Gerald S. Shadel
- Department of Pathology, Yale University School of Medicine, New Haven, Connecticut 06520-8023
- To whom correspondence should be addressed: Dept. of Pathology, Yale University School of Medicine, 310 Cedar St., P. O. Box 208023, New Haven, CT 06520-8023. Tel.: 203-785-2475; Fax: 203-785-2628; E-mail:
| |
Collapse
|
25
|
Bonawitz ND, Clayton DA, Shadel GS. Initiation and beyond: multiple functions of the human mitochondrial transcription machinery. Mol Cell 2007; 24:813-25. [PMID: 17189185 DOI: 10.1016/j.molcel.2006.11.024] [Citation(s) in RCA: 266] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Mitochondria contain their own DNA (mtDNA) that is expressed and replicated by nucleus-encoded factors imported into the organelle. Recently, the core human mitochondrial transcription machinery has been defined, comprising a bacteriophage-related mtRNA polymerase (POLRMT), an HMG-box transcription factor (h-mtTFA), and two transcription factors (h-mtTFB1 and h-mtTFB2) that also serve as rRNA methyltransferases. Here, we describe these transcription components as well as recent insights into the mechanism of human mitochondrial transcription initiation and its regulation. We also discuss novel roles for the mitochondrial transcription machinery beyond transcription initiation, including priming of mtDNA replication, packaging of mtDNA, coordination of ribosome biogenesis, and coupling of transcription to translation.
Collapse
Affiliation(s)
- Nicholas D Bonawitz
- Department of Pathology, Yale University School of Medicine, 310 Cedar Street, P.O. Box 208023, New Haven, Connecticut 06520, USA
| | | | | |
Collapse
|
26
|
Williams EH, Butler CA, Bonnefoy N, Fox TD. Translation initiation in Saccharomyces cerevisiae mitochondria: functional interactions among mitochondrial ribosomal protein Rsm28p, initiation factor 2, methionyl-tRNA-formyltransferase and novel protein Rmd9p. Genetics 2006; 175:1117-26. [PMID: 17194786 PMCID: PMC1840066 DOI: 10.1534/genetics.106.064576] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Rsm28p is a dispensable component of the mitochondrial ribosomal small subunit in Saccharomyces cerevisiae that is not related to known proteins found in bacteria. It was identified as a dominant suppressor of certain mitochondrial mutations that reduced translation of the COX2 mRNA. To explore further the function of Rsm28p, we isolated mutations in other genes that caused a synthetic respiratory defective phenotype together with rsm28Delta. These mutations identified three nuclear genes: IFM1, which encodes the mitochondrial translation initiation factor 2 (IF2); FMT1, which encodes the methionyl-tRNA-formyltransferase; and RMD9, a gene of unknown function. The observed genetic interactions strongly suggest that the ribosomal protein Rsm28p and Ifm1p (IF2) have similar and partially overlapping functions in yeast mitochondrial translation initiation. Rmd9p, bearing a TAP-tag, was localized to mitochondria and exhibited roughly equal distribution in soluble and membrane-bound fractions. A small fraction of the Rmd9-TAP sedimented together with presumed monosomes, but not with either individual ribosomal subunit. Thus, Rmd9 is not a ribosomal protein, but may be a novel factor associated with initiating monosomes. The poorly respiring rsm28Delta, rmd9-V363I double mutant did not have a strong translation-defective phenotype, suggesting that Rmd9p may function upstream of translation initiation, perhaps at the level of localization of mitochondrially coded mRNAs.
Collapse
Affiliation(s)
- Elizabeth H Williams
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853, USA
| | | | | | | |
Collapse
|
27
|
Bonawitz ND, Rodeheffer MS, Shadel GS. Defective mitochondrial gene expression results in reactive oxygen species-mediated inhibition of respiration and reduction of yeast life span. Mol Cell Biol 2006; 26:4818-29. [PMID: 16782871 PMCID: PMC1489155 DOI: 10.1128/mcb.02360-05] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mitochondrial dysfunction causes numerous human diseases and is widely believed to be involved in aging. However, mechanisms through which compromised mitochondrial gene expression elicits the reported variety of cellular defects remain unclear. The amino-terminal domain (ATD) of yeast mitochondrial RNA polymerase is required to couple transcription to translation during expression of mitochondrial DNA-encoded oxidative phosphorylation subunits. Here we report that several ATD mutants exhibit reduced chronological life span. The most severe of these (harboring the rpo41-R129D mutation) displays imbalanced mitochondrial translation, conditional inactivation of respiration, elevated production of reactive oxygen species (ROS), and increased oxidative stress. Reduction of ROS, via overexpression of superoxide dismutase (SOD1 or SOD2 product), not only greatly extends the life span of this mutant but also increases its ability to respire. Another ATD mutant with similarly reduced respiration (rpo41-D152A/D154A) accumulates only intermediate levels of ROS and has a less severe life span defect that is not rescued by SOD. Altogether, our results provide compelling evidence for the "vicious cycle" of mitochondrial ROS production and lead us to propose that the amount of ROS generated depends on the precise nature of the mitochondrial gene expression defect and initiates a downward spiral of oxidative stress only if a critical threshold is crossed.
Collapse
Affiliation(s)
- Nicholas D Bonawitz
- Department of Pathology, Yale University School of Medicine, 310 Cedar St., P.O. Box 208023, New Haven, CT 06520-8023, USA
| | | | | |
Collapse
|
28
|
Rogowska AT, Puchta O, Czarnecka AM, Kaniak A, Stepien PP, Golik P. Balance between transcription and RNA degradation is vital for Saccharomyces cerevisiae mitochondria: reduced transcription rescues the phenotype of deficient RNA degradation. Mol Biol Cell 2005; 17:1184-93. [PMID: 16371505 PMCID: PMC1382308 DOI: 10.1091/mbc.e05-08-0796] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The Saccharomyces cerevisiae SUV3 gene encodes the helicase component of the mitochondrial degradosome (mtEXO), the principal 3'-to-5' exoribonuclease of yeast mitochondria responsible for RNA turnover and surveillance. Inactivation of SUV3 (suv3Delta) causes multiple defects related to overaccumulation of aberrant transcripts and precursors, leading to a disruption of mitochondrial gene expression and loss of respiratory function. We isolated spontaneous suppressors that partially restore mitochondrial function in suv3Delta strains devoid of mitochondrial introns and found that they correspond to partial loss-of-function mutations in genes encoding the two subunits of the mitochondrial RNA polymerase (Rpo41p and Mtf1p) that severely reduce the transcription rate in mitochondria. These results show that reducing the transcription rate rescues defects in RNA turnover and demonstrates directly the vital importance of maintaining the balance between RNA synthesis and degradation.
Collapse
Affiliation(s)
- Agata T Rogowska
- Department of Genetics, Warsaw University, 02-106 Warsaw, Poland
| | | | | | | | | | | |
Collapse
|
29
|
Taanman JW, Llewelyn Williams S. The Human Mitochondrial Genome. OXIDATIVE STRESS AND DISEASE 2005. [DOI: 10.1201/9781420028843.ch3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
|
30
|
Abstract
Mitochondria are the central processing units for cellular energy metabolism and, in addition to carrying out oxidative phosphorylation, regulate important processes such as apoptosis and calcium homeostasis. Because mitochondria possess a genome that is central to their multiple functions, an understanding of the mechanism of mitochondrial gene expression is required to decipher the many ways mitochondrial dysfunction contributes to human disease. Towards this end, two human transcription factors that are related to rRNA methyltransferases have recently been characterized, providing new insight into the mechanism of mitochondrial transcription and a novel link to maternally inherited deafness. Furthermore, studies in the Saccharomyces cerevisiae model system have revealed a functional coupling of transcription and translation at the inner mitochondrial membrane, where assembly of the oxidative phosphorylation system commences. Defects in an analogous coupling mechanism in humans might underlie the cytochrome oxidase deficiency that causes a form of Leigh Syndrome.
Collapse
Affiliation(s)
- Gerald S Shadel
- Department of Pathology, Yale University School of Medicine, 300 Cedar Street, PO Box 208023, New Haven, CT 06520-8023, USA.
| |
Collapse
|
31
|
Abstract
Several questions in our understanding of mitochondria are unanswered. These include how the ratio of mitochondrial (mt)DNA to mitochondria is maintained, how the accumulation of defective, rapidly replicating mitochondrial DNA is avoided, how the ratio of mitochondria to cells is adjusted to fit cellular needs, and why any proteins are synthesized in mitochondria rather than simply imported. In bacteria, large hyperstructures or assemblies of proteins, mRNA, lipids and ions have been proposed to constitute a level of organization intermediate between macromolecules and whole cells. Here, we suggest how the concept of hyperstructures together with other concepts developed for bacteria such as transcriptional sensing and spontaneous segregation may provide answers to mitochondrial problems. In doing this, we show how the problem of the very existence of mtDNA brings its own solution.
Collapse
Affiliation(s)
- Mirella Trinei
- Department of Experimental Oncology, European Institute of Oncology, 20141 Milan, Italy
| | | | | | | |
Collapse
|
32
|
Sellem CH, Lemaire C, Lorin S, Dujardin G, Sainsard-Chanet A. Interaction between the oxa1 and rmp1 genes modulates respiratory complex assembly and life span in Podospora anserina. Genetics 2004; 169:1379-89. [PMID: 15545650 PMCID: PMC1449539 DOI: 10.1534/genetics.104.033837] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
A causal link between deficiency of the cytochrome respiratory pathway and life span was previously shown in the filamentous fungus Podospora anserina. To gain more insight into the relationship between mitochondrial function and life span, we have constructed a strain carrying a thermosensitive mutation of the gene oxa1. OXA1 is a membrane protein conserved from bacteria to human. The mitochondrial OXA1 protein is involved in the assembly/insertion of several respiratory complexes. We show here that oxa1 is an essential gene in P. anserina. The oxa1(ts) mutant exhibits severe defects in the respiratory complexes I and IV, which are correlated with an increased life span, a strong induction of the alternative oxidase, and a reduction in ROS production. However, there is no causal link between alternative oxidase level and life span. We also show that in the oxa1(ts) mutant, the extent of the defects in complexes I and IV and the life-span increase depends on the essential gene rmp1. The RMP1 protein, whose function is still unknown, can be localized in the mitochondria and/or the cytosolic compartment, depending on the developmental stage. We propose that the RMP1 protein could be involved in the process of OXA1-dependent protein insertion.
Collapse
Affiliation(s)
- Carole H Sellem
- Centre de Génétique Moléculaire UPR 2167, Associated with the University of Paris-Sud 11 CNRS, Gif-sur-Yvette, France
| | | | | | | | | |
Collapse
|
33
|
Contamine V, Zickler D, Picard M. The Podospora rmp1 gene implicated in nucleus-mitochondria cross-talk encodes an essential protein whose subcellular location is developmentally regulated. Genetics 2004; 166:135-50. [PMID: 15020413 PMCID: PMC1470695 DOI: 10.1534/genetics.166.1.135] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
It has been previously reported that, at the time of death, the Podospora anserina AS1-4 mutant strains accumulate specific deleted forms of the mitochondrial genome and that their life spans depend on two natural alleles (variants) of the rmp1 gene: AS1-4 rmp1-2 strains exhibit life spans strikingly longer than those of AS1-4 rmp1-1. Here, we show that rmp1 is an essential gene. In silico analyses of eight rmp1 natural alleles present in Podospora isolates and of the putative homologs of this orphan gene in other filamentous fungi suggest that rmp1 evolves rapidly. The RMP1 protein is localized in the mitochondrial and/or the cytosolic compartment, depending on cell type and developmental stage. Strains producing RMP1 without its mitochondrial targeting peptide are viable but exhibit vegetative and sexual defects.
Collapse
Affiliation(s)
- Véronique Contamine
- Institut de Génétique et Microbiologie, Université Paris-Sud, UMR 8621, Orsay, France
| | | | | |
Collapse
|
34
|
Krause K, Lopes de Souza R, Roberts DGW, Dieckmann CL. The mitochondrial message-specific mRNA protectors Cbp1 and Pet309 are associated in a high-molecular weight complex. Mol Biol Cell 2004; 15:2674-83. [PMID: 15047869 PMCID: PMC420092 DOI: 10.1091/mbc.e04-02-0126] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
In Saccharomyces cerevisiae, the nuclear-encoded protein Cbp1 promotes stability and translation of mitochondrial cytochrome b transcripts through interaction with the 5' untranslated region. Fusion of a biotin binding peptide tag to the C terminus of Cbp1 has now allowed detection in mitochondrial extracts by using peroxidase-coupled avidin. Cbp1 is associated with the mitochondrial membranes when high ionic strength extraction conditions are used. However, the protein is easily solubilized by omitting salt from the extraction buffer, which suggests Cbp1 is loosely associated with the membrane through weak hydrophobic interactions. Gel filtration analysis and blue native PAGE showed that Cbp1 is part of a single 900,000-Da complex. The complex was purified using the biotin tag and a sequence-specific protease cleavage site. In addition to Cbp1, the complex contains several polypeptides of molecular weights between 113 and 40 kDa. Among these, we identified another message-specific factor, Pet309, which promotes the stability and translation of mitochondrial cytochrome oxidase subunit I mRNA. A hypothesis is presented in which the Cbp1-Pet309 complex contains several message-specific RNA binding proteins and links transcription to translation of the mRNAs at the membrane.
Collapse
Affiliation(s)
- Kirsten Krause
- Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, Arizona 85721, USA
| | | | | | | |
Collapse
|
35
|
Rodeheffer MS, Shadel GS. Multiple interactions involving the amino-terminal domain of yeast mtRNA polymerase determine the efficiency of mitochondrial protein synthesis. J Biol Chem 2003; 278:18695-701. [PMID: 12637560 PMCID: PMC2606056 DOI: 10.1074/jbc.m301399200] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The amino-terminal domain (ATD) of Saccharomyces cerevisiae mitochondrial RNA polymerase has been shown to provide a functional link between transcription and post-transcriptional events during mitochondrial gene expression. This connection is mediated in large part by its interactions with the matrix protein Nam1p and, based on genetic phenotypes, the mitochondrial membrane protein Sls1p. These observations led us to propose previously that mtRNA polymerase, Nam1p, and Sls1p work together to coordinate transcription and translation of mtDNA-encoded gene products. Here we demonstrate by specific labeling of mitochondrial gene products in vivo that Nam1p and Sls1p indeed work together in a pathway that is required globally for efficient mitochondrial translation. Likewise, mutations in the ATD result in similar global reductions in mitochondrial translation efficiency and sensitivity to the mitochondrial translation inhibitor erythromycin. These data, coupled with the observation that the ATD is required to co-purify Sls1p in association with mtDNA nucleoids, suggest that efficient expression of mtDNA-encoded genes in yeast involves a complex series of interactions that localize active transcription complexes to the inner membrane in order to coordinate translation with transcription.
Collapse
Affiliation(s)
- Matthew S. Rodeheffer
- Department of Biochemistry and the Graduate Program in Biochemistry, Cell and Developmental Biology, Rollins Research Center, Emory University School of Medicine, Atlanta, Georgia 30322-3050
| | - Gerald S. Shadel
- To whom correspondence should be addressed. Tel.: 404-727-3798; Fax: 404-727-3954; E-mail:
| |
Collapse
|
36
|
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.
Collapse
Affiliation(s)
- Sushma Naithani
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703, USA
| | | | | | | |
Collapse
|
37
|
Coelho PSR, Bryan AC, Kumar A, Shadel GS, Snyder M. A novel mitochondrial protein, Tar1p, is encoded on the antisense strand of the nuclear 25S rDNA. Genes Dev 2002; 16:2755-60. [PMID: 12414727 PMCID: PMC187471 DOI: 10.1101/gad.1035002] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2002] [Accepted: 09/11/2002] [Indexed: 12/31/2022]
Abstract
In eukaryotes, it is widely assumed that genes coding for proteins and structural RNAs do not overlap. Using a transposon-tagging strategy to globally analyze the Saccharomyces cerevisiae genome for expressed genes, we identified multiple insertions in an open reading frame that is contained fully within and transcribed antisense to the 25S rRNA gene in the nuclear rDNA repeat region on Chromosome XII. Expression of this gene, TAR1 (Transcript Antisense to Ribosomal RNA), can be detected at the RNA and protein levels, and the primary sequence of the corresponding 124-amino-acid protein is conserved in several yeast species. Tar1p was found to localize to mitochondria, and overexpression of the protein suppresses the respiration-deficient petite phenotype of a point mutation in mitochondrial RNA polymerase that affects mitochondrial gene expression and mtDNA stability. These findings indicate that coding information for protein and structural RNAs can overlap, raising issues regarding the coevolution of such complex genes, and also suggest that rDNA transcription and mitochondrial function are coordinately regulated in eukaryotic cells.
Collapse
Affiliation(s)
- Paulo S R Coelho
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103, USA
| | | | | | | | | |
Collapse
|