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Jia C, Chai R, Zhang M, Guo X, Zhou X, Ding N, Lei C, Dong Z, Zhao J, Ren H, Lu D. Improvement of Saccharomyces cerevisiae strain tolerance to vanillin through heavy ion radiation combined with adaptive laboratory evolution. J Biotechnol 2024; 394:112-124. [PMID: 39197754 DOI: 10.1016/j.jbiotec.2024.08.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2024] [Revised: 08/12/2024] [Accepted: 08/23/2024] [Indexed: 09/01/2024]
Abstract
Vanillin is an inhibitor of lignocellulose hydrolysate, which can reduce the ability of Saccharomyces cerevisiae to utilize lignocellulose, which is an important factor limiting the development of the ethanol fermentation industry. In this study, mutants of vanillin-tolerant yeast named H6, H7, X3, and X8 were bred by heavy ion irradiation (HIR) combined with adaptive laboratory evolution (ALE). Phenotypic tests revealed that the mutants outperformed the original strain WT in tolerance, growth rate, genetic stability and fermentation ability. At 1.6 g/L vanillin concentration, the average OD600 value obtained for mutant strains was 0.95 and thus about 3.4-fold higher than for the wild-type. When the concentration of vanillin was 2.0 g/L, the glucose utilization rate of the mutant was 86.3 % within 96 h, while that of the original strain was only 70.0 %. At this concentration of vanillin, the mitochondrial membrane potential of the mutant strain recovered faster than that of the original strain, and the ROS scavenging ability was stronger. We analyzed the whole transcriptome sequencing map and the whole genome resequencing of the mutant, and found that DEGs such as FLO9, GRC3, PSP2 and SWF1, which have large differential expression multiples and obvious mutation characteristics, play an important role in cell flocculation, rDNA transcription, inhibition of DNA polymerase mutation and protein palmitoylation. These functions can help cells resist vanillin stress. The results show that combining HIR with ALE is an effective mutagenesis strategy. This approach can efficiently obtain Saccharomyces cerevisiae mutants with improved vanillin tolerance, and provide reference for obtaining robust yeast strains with lignocellulose inhibitor tolerance.
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Affiliation(s)
- Chenglin Jia
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Ran Chai
- School of Life Science and Engineering, Lanzhou University of Technology, Lanzhou 730050, China
| | - Miaomiao Zhang
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xiaopeng Guo
- School of Life Science and Engineering, Lanzhou University of Technology, Lanzhou 730050, China.
| | - Xiang Zhou
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Nan Ding
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Cairong Lei
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Ziyi Dong
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jingru Zhao
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Haiwei Ren
- School of Life Science and Engineering, Lanzhou University of Technology, Lanzhou 730050, China
| | - Dong Lu
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China; University of Chinese Academy of Sciences, Beijing 100049, China.
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van de Poll F, Sutter BM, Acoba MG, Caballero D, Jahangiri S, Yang YS, Lee CD, Tu BP. Pbp1 associates with Puf3 and promotes translation of its target mRNAs involved in mitochondrial biogenesis. PLoS Genet 2023; 19:e1010774. [PMID: 37216416 PMCID: PMC10237644 DOI: 10.1371/journal.pgen.1010774] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Revised: 06/02/2023] [Accepted: 05/07/2023] [Indexed: 05/24/2023] Open
Abstract
Pbp1 (poly(A)-binding protein-binding protein 1) is a cytoplasmic stress granule marker that is capable of forming condensates that function in the negative regulation of TORC1 signaling under respiratory conditions. Polyglutamine expansions in its mammalian ortholog ataxin-2 lead to spinocerebellar dysfunction due to toxic protein aggregation. Here, we show that loss of Pbp1 in S. cerevisiae leads to decreased amounts of mRNAs and mitochondrial proteins which are targets of Puf3, a member of the PUF (Pumilio and FBF) family of RNA-binding proteins. We found that Pbp1 supports the translation of Puf3-target mRNAs in respiratory conditions, such as those involved in the assembly of cytochrome c oxidase and subunits of mitochondrial ribosomes. We further show that Pbp1 and Puf3 interact through their respective low complexity domains, which is required for Puf3-target mRNA translation. Our findings reveal a key role for Pbp1-containing assemblies in enabling the translation of mRNAs critical for mitochondrial biogenesis and respiration. They may further explain prior associations of Pbp1/ataxin-2 with RNA, stress granule biology, mitochondrial function, and neuronal health.
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Affiliation(s)
- Floortje van de Poll
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Benjamin M. Sutter
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Michelle Grace Acoba
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Daniel Caballero
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Samira Jahangiri
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Yu-San Yang
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Chien-Der Lee
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Benjamin P. Tu
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
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3
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Mitoferrin, Cellular and Mitochondrial Iron Homeostasis. Cells 2022; 11:cells11213464. [PMID: 36359860 PMCID: PMC9658796 DOI: 10.3390/cells11213464] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Revised: 10/28/2022] [Accepted: 10/29/2022] [Indexed: 11/06/2022] Open
Abstract
Iron is essential for many cellular processes, but cellular iron homeostasis must be maintained to ensure the balance of cellular signaling processes and prevent disease. Iron transport in and out of the cell and cellular organelles is crucial in this regard. The transport of iron into the mitochondria is particularly important, as heme and the majority of iron-sulfur clusters are synthesized in this organelle. Iron is also required for the production of mitochondrial complexes that contain these iron-sulfur clusters and heme. As the principal iron importers in the mitochondria of human cells, the mitoferrins have emerged as critical regulators of cytosolic and mitochondrial iron homeostasis. Here, we review the discovery and structure of the mitoferrins, as well as the significance of these proteins in maintaining cytosolic and mitochondrial iron homeostasis for the prevention of cancer and many other diseases.
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Garg M, Roy D, Rajyaguru PI. Low complexity RGG-motif containing proteins Scd6 and Psp2 act as suppressors of clathrin heavy chain deficiency. BIOCHIMICA ET BIOPHYSICA ACTA. MOLECULAR CELL RESEARCH 2022; 1869:119327. [PMID: 35901970 DOI: 10.1016/j.bbamcr.2022.119327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2022] [Revised: 07/05/2022] [Accepted: 07/11/2022] [Indexed: 06/15/2023]
Abstract
Clathrin, made up of the heavy- and light-chains, constitutes one of the most abundant proteins involved in intracellular protein trafficking and endocytosis. YPR129W, which encodes RGG-motif containing translation repressor was identified as a part of the multi-gene construct (SCD6) that suppressed clathrin deficiency. However, the contribution of YPR129W alone in suppressing clathrin deficiency has not been documented. This study identifies YPR129W as a necessary and sufficient gene in a multi-gene construct SCD6 that suppresses clathrin deficiency. Importantly, we also identify cytoplasmic RGG-motif protein encoding gene PSP2 as another novel suppressor of clathrin deficiency. Detailed domain analysis of the two suppressors reveals that the RGG-motif of both Scd6 and Psp2 is important for suppressing clathrin deficiency. Interestingly, the endocytosis function of clathrin heavy chain assayed by internalization of GFP-Snc1 and α-factor secretion activity are not complemented by either Scd6 or Psp2. We further observe that inhibition of TORC1 compromises the suppression activity of both SCD6 and PSP2 to different extent, suggesting that two suppressors are differentially regulated. Scd6 granules increased based on its RGG-motif upon Chc1 depletion. Strikingly, Psp2 overexpression increased the abundance of ubiquitin-conjugated proteins in Chc1 depleted cells in its RGG-motif dependent manner and also decreased the accumulation of GFP-Atg8 foci. Overall based on our results using SCD6 and PSP2, we identify a novel role of RGG-motif containing proteins in suppressing clathrin deficiency. Since both the suppressors are RNA-binding proteins, this study opens an exciting avenue for exploring the connection between clathrin function and post-transcriptional gene control processes.
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Affiliation(s)
- Mani Garg
- Department of Biochemistry, Indian Institute of Science, C V Raman road, Bangalore 560012, India
| | - Debadrita Roy
- Department of Biochemistry, Indian Institute of Science, C V Raman road, Bangalore 560012, India
| | - Purusharth I Rajyaguru
- Department of Biochemistry, Indian Institute of Science, C V Raman road, Bangalore 560012, India.
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5
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Dzedze N, Van Breda V, Hart R, Van Wyk J. Wine chemical, sensory, aroma compound and protein analysis of wines produced from chemical and biological fungicide treated Chenin blanc grapes. Food Control 2019. [DOI: 10.1016/j.foodcont.2019.06.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Ogunbona OB, Claypool SM. Emerging Roles in the Biogenesis of Cytochrome c Oxidase for Members of the Mitochondrial Carrier Family. Front Cell Dev Biol 2019; 7:3. [PMID: 30766870 PMCID: PMC6365663 DOI: 10.3389/fcell.2019.00003] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2018] [Accepted: 01/10/2019] [Indexed: 12/11/2022] Open
Abstract
The mitochondrial carrier family (MCF) is a group of transport proteins that are mostly localized to the inner mitochondrial membrane where they facilitate the movement of various solutes across the membrane. Although these carriers represent potential targets for therapeutic application and are repeatedly associated with human disease, research on the MCF has not progressed commensurate to their physiologic and pathophysiologic importance. Many of the 53 MCF members in humans are orphans and lack known transport substrates. Even for the relatively well-studied members of this family, such as the ADP/ATP carrier and the uncoupling protein, there exist fundamental gaps in our understanding of their biological roles including a clear rationale for the existence of multiple isoforms. Here, we briefly review this important family of mitochondrial carriers, provide a few salient examples of their diverse metabolic roles and disease associations, and then focus on an emerging link between several distinct MCF members, including the ADP/ATP carrier, and cytochrome c oxidase biogenesis. As the ADP/ATP carrier is regarded as the paradigm of the entire MCF, its newly established role in regulating translation of the mitochondrial genome highlights that we still have a lot to learn about these metabolite transporters.
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Affiliation(s)
- Oluwaseun B. Ogunbona
- Department of Physiology, School of Medicine, Johns Hopkins University, Baltimore, MD, United States
- Department of Pathology & Laboratory Medicine, School of Medicine, Emory University, Atlanta, GA, United States
| | - Steven M. Claypool
- Department of Physiology, School of Medicine, Johns Hopkins University, Baltimore, MD, United States
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7
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Meza Gutierrez F, Simsek D, Mizrak A, Deutschbauer A, Braberg H, Johnson J, Xu J, Shales M, Nguyen M, Tamse-Kuehn R, Palm C, Steinmetz LM, Krogan NJ, Toczyski DP. Genetic analysis reveals functions of atypical polyubiquitin chains. eLife 2018; 7:42955. [PMID: 30547882 PMCID: PMC6305200 DOI: 10.7554/elife.42955] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2018] [Accepted: 11/30/2018] [Indexed: 12/27/2022] Open
Abstract
Although polyubiquitin chains linked through all lysines of ubiquitin exist, specific functions are well-established only for lysine-48 and lysine-63 linkages in Saccharomyces cerevisiae. To uncover pathways regulated by distinct linkages, genetic interactions between a gene deletion library and a panel of lysine-to-arginine ubiquitin mutants were systematically identified. The K11R mutant had strong genetic interactions with threonine biosynthetic genes. Consistently, we found that K11R mutants import threonine poorly. The K11R mutant also exhibited a strong genetic interaction with a subunit of the anaphase-promoting complex (APC), suggesting a role in cell cycle regulation. K11-linkages are important for vertebrate APC function, but this was not previously described in yeast. We show that the yeast APC also modifies substrates with K11-linkages in vitro, and that those chains contribute to normal APC-substrate turnover in vivo. This study reveals comprehensive genetic interactomes of polyubiquitin chains and characterizes the role of K11-chains in two biological pathways.
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Affiliation(s)
- Fernando Meza Gutierrez
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
| | | | - Arda Mizrak
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
| | | | - Hannes Braberg
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, United States
| | - Jeffrey Johnson
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, United States
| | - Jiewei Xu
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, United States
| | - Michael Shales
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, United States
| | - Michelle Nguyen
- Stanford Genome Technology Center, Stanford University, Stanford, United States
| | - Raquel Tamse-Kuehn
- Stanford Genome Technology Center, Stanford University, Stanford, United States
| | - Curt Palm
- Stanford Genome Technology Center, Stanford University, Stanford, United States
| | - Lars M Steinmetz
- Stanford Genome Technology Center, Stanford University, Stanford, United States
| | - Nevan J Krogan
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, United States
| | - David P Toczyski
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
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8
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Špírek M, Poláková S, Jatzová K, Sulo P. Post-zygotic sterility and cytonuclear compatibility limits in S. cerevisiae xenomitochondrial cybrids. Front Genet 2015; 5:454. [PMID: 25628643 PMCID: PMC4290679 DOI: 10.3389/fgene.2014.00454] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Accepted: 12/11/2014] [Indexed: 12/04/2022] Open
Abstract
Nucleo-mitochondrial interactions, particularly those determining the primary divergence of biological species, can be studied by means of xenomitochondrial cybrids, which are cells where the original mitochondria are substituted by their counterparts from related species. Saccharomyces cerevisiae cybrids are prepared simply by the mating of the ρ(0) strain with impaired karyogamy and germinating spores from other Saccharomyces species and fall into three categories. Cybrids with compatible mitochondrial DNA (mtDNA) from Saccharomyces paradoxus CBS 432 and Saccharomyces cariocanus CBS 7994 are metabolically and genetically similar to cybrids containing mtDNA from various S. cerevisiae. Cybrids with mtDNA from other S. paradoxus strains, S. cariocanus, Saccharomyces kudriavzevii, and Saccharomyces mikatae require a period of adaptation to establish efficient oxidative phosphorylation. They exhibit a temperature-sensitive phenotype, slower growth rate on a non-fermentable carbon source and a long lag phase after the shift from glucose. Their decreased respiration capacity and reduced cytochrome aa3 content is associated with the inefficient splicing of cox1I3β, the intron found in all Saccharomyces species but not in S. cerevisiae. The splicing defect is compensated in cybrids by nuclear gain-of-function and can be alternatively suppressed by overexpression of MRP13 gene for mitochondrial ribosomal protein or the MRS2, MRS3, and MRS4 genes involved in intron splicing. S. cerevisiae with Saccharomyces bayanus mtDNA is unable to respire and the growth on ethanol-glycerol can be restored only after mating to some mit (-) strains. The nucleo-mitochondrial compatibility limit of S. cerevisiae and other Saccharomyces was set between S. kudriavzevii and S. bayanus at the divergence from S. cerevisiae about 15 MYA. The MRS1-cox1 S. cerevisiae/S. paradoxus cytonuclear Dobzhansky-Muller pair has a neglible impact on the separation of species since its imperfection is compensated for by gain-of-function mutation.
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Affiliation(s)
| | | | | | - Pavol Sulo
- *Correspondence: Pavol Sulo, Department of Biochemistry, Faculty of Natural Sciences, Comenius University, Mlynská Dolina, 842 15 Bratislava, Slovakia e-mail:
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9
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Jain A, Connolly EL. Mitochondrial iron transport and homeostasis in plants. FRONTIERS IN PLANT SCIENCE 2013; 4:348. [PMID: 24046773 PMCID: PMC3764374 DOI: 10.3389/fpls.2013.00348] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2013] [Accepted: 08/18/2013] [Indexed: 05/20/2023]
Abstract
Iron (Fe) is an essential nutrient for plants and although the mechanisms controlling iron uptake from the soil are relatively well understood, comparatively little is known about subcellular trafficking of iron in plant cells. Mitochondria represent a significant iron sink within cells, as iron is required for the proper functioning of respiratory chain protein complexes. Mitochondria are a site of Fe-S cluster synthesis, and possibly heme synthesis as well. Here we review recent insights into the molecular mechanisms controlling mitochondrial iron transport and homeostasis. We focus on the recent identification of a mitochondrial iron uptake transporter in rice and a possible role for metalloreductases in iron uptake by mitochondria. In addition, we highlight recent advances in mitochondrial iron homeostasis with an emphasis on the roles of frataxin and ferritin in iron trafficking and storage within mitochondria.
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Affiliation(s)
| | - Erin L. Connolly
- *Correspondence: Erin L. Connolly, University of South Carolina, 715 Sumter Street, Columbia, SC 29208, USA e-mail:
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Nowikovsky K, Pozzan T, Rizzuto R, Scorrano L, Bernardi P. Perspectives on: SGP symposium on mitochondrial physiology and medicine: the pathophysiology of LETM1. ACTA ACUST UNITED AC 2013; 139:445-54. [PMID: 22641639 PMCID: PMC3362517 DOI: 10.1085/jgp.201110757] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Karin Nowikovsky
- Department of Internal Medicine 1, Anna Spiegel Center of Translational Research, Medical University Vienna, 1090 Wien, Austria.
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11
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Affiliation(s)
- Georg W J Auburger
- Section Molecular Neurogenetics, Department of Neurology, Johann Wolfgang Goeche University Medical School, Frankfurt/Main, Germany.
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12
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Deleterious effect of the Qo inhibitor compound resistance-conferring mutation G143A in the intron-containing cytochrome b gene and mechanisms for bypassing it. Appl Environ Microbiol 2011; 77:2088-93. [PMID: 21278281 DOI: 10.1128/aem.02548-10] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mutation G143A in the inhibitor binding site of cytochrome b confers a high level of resistance to fungicides targeting the bc(1) complex. The mutation, reported in many plant-pathogenic fungi, has not evolved in fungi that harbor an intron immediately after the codon for G143 in the cytochrome b gene, intron bi2. Using Saccharomyces cerevisiae as a model organism, we show here that a codon change from GGT to GCT, which replaces glycine 143 with alanine, hinders the splicing of bi2 by altering the exon/intron structure needed for efficient intron excision. This lowers the levels of cytochrome b and respiratory growth. We then investigated possible bypass mechanisms that would restore the respiratory fitness of a resistant mutant. Secondary mutations in the mitochondrial genome were found, including a point mutation in bi2 restoring the correct exon/intron structure and the deletion of intron bi2. We also found that overexpression of nuclear genes MRS2 and MRS3, encoding mitochondrial metal ion carriers, partially restores the respiratory growth of the G143A mutant. Interestingly, the MRS3 gene from the plant-pathogenic fungus Botrytis cinerea, overexpressed in an S. cerevisiae G143A mutant, had a similar compensatory effect. These bypass mechanisms identified in yeast could potentially arise in pathogenic fungi.
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Zhao J, Lin W, Ma X, Lu Q, Ma X, Bian G, Jiang L. The protein kinase Hal5p is the high-copy suppressor of lithium-sensitive mutations of genes involved in the sporulation and meiosis as well as the ergosterol biosynthesis in Saccharomyces cerevisiae. Genomics 2010; 95:290-8. [PMID: 20206679 DOI: 10.1016/j.ygeno.2010.02.010] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2009] [Revised: 02/25/2010] [Accepted: 02/25/2010] [Indexed: 11/30/2022]
Abstract
From a genome-scale genetic screen, we have identified 114 lithium-sensitive and 6 lithium-tolerant gene mutations in Saccharomyces cerevisiae. Twenty-five of these identified lithium-sensitive mutations are of genes previously reported to be involved in sporulation and meiosis, whereas thirty-six of them are of genes involved in the vacuolar protein sorting (VPS) pathway, mainly functioning in the membrane docking and fusion. Accordingly, the lithium-sensitive phenotypes for one third of identified VPS mutants well correlate to their intracellular lithium contents in response to lithium stress. This indicates the integrity of the VPS pathway is critic for the ion homeostasis in yeast cells. The halotolerant protein kinase Hal5p, a regulator of the potassium transporter Trk1p, is shown to be the high-copy suppressor of nearly one third of identified lithium-sensitive mutations of genes involved in the sporulation and meiosis as well as in the biosynthesis of ergosterol. These results suggest that Hal5p-mediated ion homeostasis is important for these two biological processes.
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Affiliation(s)
- Jingwen Zhao
- Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, China
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14
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Zotova L, Aleschko M, Sponder G, Baumgartner R, Reipert S, Prinz M, Schweyen RJ, Nowikovsky K. Novel components of an active mitochondrial K(+)/H(+) exchange. J Biol Chem 2010; 285:14399-414. [PMID: 20197279 DOI: 10.1074/jbc.m109.059956] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Defects of the mitochondrial K(+)/H(+) exchanger (KHE) result in increased matrix K(+) content, swelling, and autophagic decay of the organelle. We have previously identified the yeast Mdm38 and its human homologue LETM1, the candidate gene for seizures in Wolf-Hirschhorn syndrome, as essential components of the KHE. In a genome-wide screen for multicopy suppressors of the pet(-) (reduced growth on nonfermentable substrate) phenotype of mdm38Delta mutants, we now characterized the mitochondrial carriers PIC2 and MRS3 as moderate suppressors and MRS7 and YDL183c as strong suppressors. Like Mdm38p, Mrs7p and Ydl183cp are mitochondrial inner membrane proteins and constituents of approximately 500-kDa protein complexes. Triple mutant strains (mdm38Delta mrs7Delta ydl183cDelta) exhibit a remarkably stronger pet(-) phenotype than mdm38Delta and a general growth reduction. They totally lack KHE activity, show a dramatic drop of mitochondrial membrane potential, and heavy fragmentation of mitochondria and vacuoles. Nigericin, an ionophore with KHE activity, fully restores growth of the triple mutant, indicating that loss of KHE activity is the underlying cause of its phenotype. Mdm38p or overexpression of Mrs7p, Ydl183cp, or LETM1 in the triple mutant rescues growth and KHE activity. A LETM1 human homologue, HCCR-1/LETMD1, described as an oncogene, partially suppresses the yeast triple mutant phenotype. Based on these results, we propose that Ydl183p and the Mdm38p homologues Mrs7p, LETM1, and HCCR-1 are involved in the formation of an active KHE system.
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Affiliation(s)
- Ludmila Zotova
- Department of Microbiology, Max F. Perutz Laboratories, Vienna University, A-1030 Vienna, Austria
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15
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Froschauer EM, Schweyen RJ, Wiesenberger G. The yeast mitochondrial carrier proteins Mrs3p/Mrs4p mediate iron transport across the inner mitochondrial membrane. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:1044-50. [PMID: 19285482 DOI: 10.1016/j.bbamem.2009.03.004] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2008] [Revised: 11/28/2008] [Accepted: 03/05/2009] [Indexed: 11/16/2022]
Abstract
The yeast proteins Mrs3p and Mrs4p are two closely related members of the mitochondrial carrier family (MCF), which had previously been implicated in mitochondrial Fe(2+) homeostasis. A vertebrate Mrs3/4 homologue named mitoferrin was shown to be essential for erythroid iron utilization and proposed to function as an essential mitochondrial iron importer. Indirect reporter assays in isolated yeast mitochondria indicated that the Mrs3/4 proteins are involved in mitochondrial Fe(2+) utilization or transport under iron-limiting conditions. To have a more direct test for Mrs3/4p mediated iron uptake into mitochondria we studied iron (II) transport across yeast inner mitochondrial membrane vesicles (SMPs) using the iron-sensitive fluorophore PhenGreen SK (PGSK). Wild-type SMPs showed rapid uptake of Fe(2+) which was driven by the external Fe(2+) concentration and stimulated by acidic pH. SMPs from the double deletion strain mrs3/4Delta failed to show this rapid Fe(2+) uptake, while SMPs from cells overproducing Mrs3/4p exhibited increased Fe(2+) uptake rates. Cu(2+) was transported at similar rates as Fe(2+), while other divalent cations, such as Zn(2+) and Cd(2+) apparently did not serve as substrates for the Mrs3/4p transporters. We conclude that the carrier proteins Mrs3p and Mrs4p transport Fe(2+) across the inner mitochondrial membrane. Their activity is dependent on the pH gradient and it is stimulated by iron shortage.
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Affiliation(s)
- Elisabeth M Froschauer
- Max F. Perutz Laboratories, Department of Genetics, University of Vienna, Dr. Bohrgasse 9, A-1030 Vienna, Austria
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16
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Tamai S, Iida H, Yokota S, Sayano T, Kiguchiya S, Ishihara N, Hayashi JI, Mihara K, Oka T. Characterization of the mitochondrial protein LETM1, which maintains the mitochondrial tubular shapes and interacts with the AAA-ATPase BCS1L. J Cell Sci 2008; 121:2588-600. [PMID: 18628306 DOI: 10.1242/jcs.026625] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
LETM1 is located in the chromosomal region that is deleted in patients suffering Wolf-Hirschhorn syndrome; it encodes a homolog of the yeast protein Mdm38 that is involved in mitochondrial morphology. Here, we describe the LETM1-mediated regulation of the mitochondrial volume and its interaction with the mitochondrial AAA-ATPase BCS1L that is responsible for three different human disorders. LETM1 is a mitochondrial inner-membrane protein with a large domain extruding to the matrix. The LETM1 homolog LETM2 is a mitochondrial protein that is expressed preferentially in testis and sperm. LETM1 downregulation caused mitochondrial swelling and cristae disorganization, but seemed to have little effect on membrane fusion and fission. Formation of the respiratory-chain complex was impaired by LETM1 knockdown. Cells lacking mitochondrial DNA lost active respiratory chains but maintained mitochondrial tubular networks, indicating that mitochondrial swelling caused by LETM1 knockdown is not caused by the disassembly of the respiratory chains. LETM1 was co-precipitated with BCS1L and formation of the LETM1 complex depended on BCS1L levels, suggesting that BCS1L stimulates the assembly of the LETM1 complex. BCS1L knockdown caused disassembly of the respiratory chains as well as LETM1 downregulation and induced distinct changes in mitochondrial morphology.
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Affiliation(s)
- Shoko Tamai
- Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka, Japan
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17
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Papp-Wallace KM, Maguire ME. Bacterial homologs of eukaryotic membrane proteins: the 2-TM-GxN family of Mg(2+) transporters. Mol Membr Biol 2007; 24:351-6. [PMID: 17710639 DOI: 10.1080/09687680701441883] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Magnesium is essential for all forms of life. It is the cofactor for many enzymes and plays a key role in many biological processes. Thus, the acquisition of Mg(2+) is crucial for cell survival. The best characterized Mg(2+) transporters to date belong to the 2-TM-GxN type family of transporters. The name indicates the two C-terminal transmembrane (TM) domains and a conserved GxN motif present in all members of this family towards the C-terminal end of TM1. In most members of the family, this conserved motif is generally YGMNF. The prototypical member of this family is CorA. Other characterized members of this family include Mrs2p, Alr, Mnr, AtMGT and ZntB. CorA is widely distributed throughout the prokaryotic world. It is the primary Mg(2+) uptake system in most bacteria and many Archaea. A homolog, Mrs2p, is a eukaryotic mitochondrial Mg(2+) channel. The Mrs2p related AtMGT transporters are found in plants and other eukaryotes. Alr1p and Mnr are Mg(2+) transporters found in the plasma membrane of many fungi. ZntB is a bacterial member of the 2-TM-GxN family but mediates efflux of Zn(2+) instead of influx of Mg(2+). The recent crystal structure of a bacterial CorA shows that the structure of this family is unlike that of any other class of transporter or channel currently known.
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Affiliation(s)
- Krisztina M Papp-Wallace
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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18
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Hwang DK, Claypool SM, Leuenberger D, Tienson HL, Koehler CM. Tim54p connects inner membrane assembly and proteolytic pathways in the mitochondrion. ACTA ACUST UNITED AC 2007; 178:1161-75. [PMID: 17893242 PMCID: PMC2064651 DOI: 10.1083/jcb.200706195] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Tim54p, a component of the inner membrane TIM22 complex, does not directly mediate the import of inner membrane substrates but is required for assembly/stability of the 300-kD TIM22 complex. In addition, Δtim54 yeast exhibit a petite-negative phenotype (also observed in yeast harboring mutations in the F1Fo ATPase, the ADP/ATP carrier, mitochondrial morphology components, or the i–AAA protease, Yme1p). Interestingly, other import mutants in our strain background are not petite-negative. We report that Tim54p is not involved in maintenance of mitochondrial DNA or mitochondrial morphology. Rather, Tim54p mediates assembly of an active Yme1p complex, after Yme1p is imported via the TIM23 pathway. Defective Yme1p assembly is likely the major contributing factor for the petite-negativity in strains lacking functional Tim54p. Thus, Tim54p has two independent functions: scaffolding/stability for the TIM22 membrane complex and assembly of Yme1p into a proteolytically active complex. As such, Tim54p links protein import, assembly, and turnover pathways in the mitochondrion.
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Affiliation(s)
- David K Hwang
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
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19
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Ralser M, Albrecht M, Nonhoff U, Lengauer T, Lehrach H, Krobitsch S. An Integrative Approach to Gain Insights into the Cellular Function of Human Ataxin-2. J Mol Biol 2005; 346:203-14. [PMID: 15663938 DOI: 10.1016/j.jmb.2004.11.024] [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: 10/05/2004] [Accepted: 11/05/2004] [Indexed: 10/26/2022]
Abstract
Spinocerebellar ataxia type 2 (SCA2) is a hereditary neurodegenerative disorder caused by a trinucleotide expansion in the SCA2 gene, encoding a polyglutamine stretch in the gene product ataxin-2 (ATX2), whose cellular function is unknown. However, ATX2 interacts with A2BP1, a protein containing an RNA-recognition motif, and the existence of an interaction motif for the C-terminal domain of the poly(A)-binding protein (PABC) as well as an Lsm (Like Sm) domain in ATX2 suggest that ATX2 like its yeast homolog Pbp1 might be involved in RNA metabolism. Here, we show that, similar to Pbp1, ATX2 suppresses the petite (pet-) phenotype of Deltamrs2 yeast strains lacking mitochondrial group II introns. This finding points to a close functional relationship between the two homologs. To gain insight into potential functions of ATX2, we also generated a comprehensive protein interaction network for Pbp1 from publicly available databases, which implicates Pbp1 in diverse RNA-processing pathways. The functional relationship of ATX2 and Pbp1 is further corroborated by the experimental confirmation of the predicted interaction of ATX2 with the cytoplasmic poly(A)-binding protein 1 (PABP) using yeast-2-hybrid analysis as well as co-immunoprecipitation experiments. Immunofluorescence studies revealed that ATX2 and PABP co-localize in mammalian cells, remarkably, even under conditions in which PABP accumulates in distinct cytoplasmic foci representing sites of mRNA triage.
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Affiliation(s)
- Markus Ralser
- Max Planck Institute for Molecular Genetics, Ihnestrasse 73, 14195 Berlin, Germany
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20
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Malagon F, Tong AH, Shafer BK, Strathern JN. Genetic interactions of DST1 in Saccharomyces cerevisiae suggest a role of TFIIS in the initiation-elongation transition. Genetics 2004; 166:1215-27. [PMID: 15082542 PMCID: PMC1470799 DOI: 10.1534/genetics.166.3.1215] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
TFIIS promotes the intrinsic ability of RNA polymerase II to cleave the 3'-end of the newly synthesized RNA. This stimulatory activity of TFIIS, which is dependent upon Rpb9, facilitates the resumption of transcription elongation when the polymerase stalls or arrests. While TFIIS has a pronounced effect on transcription elongation in vitro, the deletion of DST1 has no major effect on cell viability. In this work we used a genetic approach to increase our knowledge of the role of TFIIS in vivo. We showed that: (1) dst1 and rpb9 mutants have a synthetic growth defective phenotype when combined with fyv4, gim5, htz1, yal011w, ybr231c, soh1, vps71, and vps72 mutants that is exacerbated during germination or at high salt concentrations; (2) TFIIS and Rpb9 are essential when the cells are challenged with microtubule-destabilizing drugs; (3) among the SDO (synthetic with Dst one), SOH1 shows the strongest genetic interaction with DST1; (4) the presence of multiple copies of TAF14, SUA7, GAL11, RTS1, and TYS1 alleviate the growth phenotype of dst1 soh1 mutants; and (5) SRB5 and SIN4 genetically interact with DST1. We propose that TFIIS is required under stress conditions and that TFIIS is important for the transition between initiation and elongation in vivo.
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Affiliation(s)
- Francisco Malagon
- Gene Regulation and Chromosome Biology Laboratory, National Cancer Institute, National Institutes of Health, Frederick, Maryland 21702, USA
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21
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Dunn CD, Jensen RE. Suppression of a defect in mitochondrial protein import identifies cytosolic proteins required for viability of yeast cells lacking mitochondrial DNA. Genetics 2004; 165:35-45. [PMID: 14504216 PMCID: PMC1462761 DOI: 10.1093/genetics/165.1.35] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The TIM22 complex, required for the insertion of imported polytopic proteins into the mitochondrial inner membrane, contains the nonessential Tim18p subunit. To learn more about the function of Tim18p, we screened for high-copy suppressors of the inability of tim18Delta mutants to live without mitochondrial DNA (mtDNA). We identified several genes encoding cytosolic proteins, including CCT6, SSB1, ICY1, TIP41, and PBP1, which, when overproduced, rescue the mtDNA dependence of tim18Delta cells. Furthermore, these same plasmids rescue the petite-negative phenotype of cells lacking other components of the mitochondrial protein import machinery. Strikingly, disruption of the genes identified by the different suppressors produces cells that are unable to grow without mtDNA. We speculate that loss of mtDNA leads to a lowered inner membrane potential, and subtle changes in import efficiency can no longer be tolerated. Our results suggest that increased amounts of Cct6p, Ssb1p, Icy1p, Tip41p, and Pbp1p help overcome the problems resulting from a defect in protein import.
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Affiliation(s)
- Cory D Dunn
- Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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22
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Nowikovsky K, Froschauer EM, Zsurka G, Samaj J, Reipert S, Kolisek M, Wiesenberger G, Schweyen RJ. The LETM1/YOL027 gene family encodes a factor of the mitochondrial K+ homeostasis with a potential role in the Wolf-Hirschhorn syndrome. J Biol Chem 2004; 279:30307-15. [PMID: 15138253 DOI: 10.1074/jbc.m403607200] [Citation(s) in RCA: 156] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The yeast open reading frames YOL027 and YPR125 and their orthologs in various eukaryotes encode proteins with a single predicted trans-membrane domain ranging in molecular mass from 45 to 85 kDa. Hemizygous deletion of their human homolog LETM1 is likely to contribute to the Wolf-Hirschhorn syndrome phenotype. We show here that in yeast and human cells, these genes encode integral proteins of the inner mitochondrial membrane. Deletion of the yeast YOL027 gene (yol027Delta mutation) results in mitochondrial dysfunction. This mutant phenotype is complemented by the expression of the human LETM1 gene in yeast, indicating a functional conservation of LetM1/Yol027 proteins from yeast to man. Mutant yol027Delta mitochondria have increased cation contents, particularly K+ and low-membrane-potential Deltapsi. They are massively swollen in situ and refractory to potassium acetate-induced swelling in vitro, which is indicative of a defect in K+/H+ exchange activity. Thus, YOL027/LETM1 are the first genes shown to encode factors involved in both K+ homeostasis and organelle volume control.
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Affiliation(s)
- Karin Nowikovsky
- Max F. Perutz Laboratories, Departments of Microbiology and Genetics, University of Vienna, Campus Vienna Biocenter, A-1030 Vienna, Austria
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23
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Schlickum S, Moghekar A, Simpson JC, Steglich C, O'Brien RJ, Winterpacht A, Endele SU. LETM1, a gene deleted in Wolf–Hirschhorn syndrome, encodes an evolutionarily conserved mitochondrial protein. Genomics 2004; 83:254-61. [PMID: 14706454 DOI: 10.1016/j.ygeno.2003.08.013] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The leucine zipper-, EF-hand-containing transmembrane protein 1 (LETM1) has recently been cloned in an attempt to identify genes deleted in Wolf-Hirschhorn syndrome (WHS), a microdeletion syndrome characterized by severe growth and mental retardation, hypotonia, seizures, and typical facial dysmorphic features. LETM1 is deleted in almost all patients with the full phenotype and has recently been suggested as an excellent candidate gene for the seizures in WHS patients. We have shown that LETM1 is evolutionarily conserved throughout the eukaryotic kingdom and exhibits homology to MDM38, a putative yeast protein involved in mitochondrial morphology. Using LETM1-EGFP fusion constructs and an anti-rat LetM1 polyclonal antibody we have demonstrated that LETM1 is located in the mitochondria. The present study presents information about a possible function for LETM1 and suggests that at least some (neuromuscular) features of WHS may be caused by mitochondrial dysfunction.
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Affiliation(s)
- Stephanie Schlickum
- Institute of Human Genetics, Friedrich-Alexander-University Erlangen-Nuremberg, Schwabachanlage 10, D-91054 Erlangen, Germany
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24
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Mühlenhoff U, Stadler JA, Richhardt N, Seubert A, Eickhorst T, Schweyen RJ, Lill R, Wiesenberger G. A specific role of the yeast mitochondrial carriers MRS3/4p in mitochondrial iron acquisition under iron-limiting conditions. J Biol Chem 2003; 278:40612-20. [PMID: 12902335 DOI: 10.1074/jbc.m307847200] [Citation(s) in RCA: 159] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The yeast genes MRS3 and MRS4 encode two members of the mitochondrial carrier family with high sequence similarity. To elucidate their function we utilized genome-wide expression profiling and found that both deletion and overexpression of MRS3/4 lead to up-regulation of several genes of the "iron regulon." We therefore analyzed the two major iron-utilizing processes, heme formation and Fe/S protein biosynthesis in vivo, in organello (intact mitochondria), and in vitro (mitochondrial extracts). Radiolabeling of yeast cells with 55Fe revealed a clear correlation between MRS3/4 expression levels and the efficiency of these biosynthetic reactions indicating a role of the carriers in utilization and/or transport of iron in vivo. Similar effects on both heme formation and Fe/S protein biosynthesis were seen in organello using mitochondria isolated from cells grown under iron-limiting conditions. The correlation between MRS3/4 expression levels and the efficiency of the two iron-utilizing processes was lost upon detergent lysis of mitochondria. As no significant changes in the mitochondrial membrane potential were observed upon overexpression or deletion of MRS3/4, our results suggest that Mrs3/4p carriers are directly involved in mitochondrial iron uptake. Mrs3/4p function in mitochondrial iron transport becomes evident under iron-limiting conditions only, indicating that the two carriers do not represent the sole system for mitochondrial iron acquisition.
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Affiliation(s)
- Ulrich Mühlenhoff
- Institut für Zytobiologie und Zytopathologie, Philipps-Universität Marburg, Robert-Koch Str 6, 35033 Marburg, Germany
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25
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Gallardo M, Luna R, Erdjument-Bromage H, Tempst P, Aguilera A. Nab2p and the Thp1p-Sac3p complex functionally interact at the interface between transcription and mRNA metabolism. J Biol Chem 2003; 278:24225-32. [PMID: 12702719 DOI: 10.1074/jbc.m302900200] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
THP1 is a conserved eukaryotic gene whose null mutations confer, in yeast, transcription and genetic instability phenotypes and RNA export defects similar to those of the THO/TREX complex null mutations. In a search for multicopy suppressors of the transcription defect of thp1Delta cells, we identified the poly(A)+ RNA-binding heterogeneous nuclear ribonucleoprotein Nab2p. Multicopy NAB2 also suppressed the RNA export defect of thp1Delta cells. This result suggests a functional relationship between Thp1p and Nab2p. Consistently, the leaky mutation nab2-1 conferred a transcription defect and hyper-recombination phenotype similar to those of thp1Delta, although to a minor degree. Reciprocally, a purified His6-tagged Thp1p fusion bound RNA in vitro. In a different approach, we show by Western analyses that a highly purified Thp1p-Sac3p complex does not contain components of THO/TREX and that sac3Delta confers a transcription defect and hyper-recombination phenotype identical to those of thp1Delta. mRNA degradation was not affected in thp1Delta mutants, implying that their expression defects are not due to mRNA decay. This indicates that Thp1p-Sac3p is a structural and functional unit. Altogether, our results suggest that Thp1p-Sac3p and Nab2p are functionally related heterogeneous nuclear ribonucleoproteins that define a further link between mRNA metabolism and transcription.
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Affiliation(s)
- Mercedes Gallardo
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Avenida Reina Mercedes 6, 41012 Sevilla, Spain
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26
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Williams EH, Fox TD. Antagonistic signals within the COX2 mRNA coding sequence control its translation in Saccharomyces cerevisiae mitochondria. RNA (NEW YORK, N.Y.) 2003; 9:419-31. [PMID: 12649494 PMCID: PMC1370409 DOI: 10.1261/rna.2182903] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2002] [Accepted: 12/16/2002] [Indexed: 05/24/2023]
Abstract
Translation of the mitochondrially coded COX2 mRNA within the organelle in yeast produces the precursor of Cox2p (pre-Cox2p), which is processed and assembled into cytochrome c oxidase. The mRNA sequence of the first 14 COX2 codons, specifying the pre-Cox2p leader peptide, was previously shown to contain a positively acting element required for translation of a mitochondrial reporter gene, ARG8(m), fused to the 91st codon of COX2. Here we show that three relatively short sequences within the COX2 mRNA coding sequence, or structures they form in vivo, inhibit translation of the reporter in the absence of the positive element. One negative element was localized within codons 15 to 25 and shown to function at the level of the mRNA sequence, whereas two others are within predicted stem-loop structures formed by codons 22-44 and by codons 46-74. All three of these inhibitory elements are antagonized in a sequence-specific manner by reintroduction of the upstream positive-acting sequence. These interactions appear to be independent of 5'- and 3'-untranslated leader sequences, as they are also observed when the same reporter constructs are expressed from the COX3 locus. Overexpression of MRS2, which encodes a mitochondrial magnesium carrier, partially suppresses translational inhibition by each isolated negatively acting element, but does not suppress them in combination. We hypothesize that interplay among these signals during translation in vivo may ensure proper timing of pre-Cox2p synthesis and assembly into cytochrome c oxidase.
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Affiliation(s)
- Elizabeth H Williams
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703, USA
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27
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Schmidt U, Lehmann K, Stahl U. A novel mitochondrial DEAD box protein (Mrh4) required for maintenance of mtDNA inSaccharomyces cerevisiae. FEMS Yeast Res 2002. [DOI: 10.1111/j.1567-1364.2002.tb00094.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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28
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Foury F, Roganti T. Deletion of the mitochondrial carrier genes MRS3 and MRS4 suppresses mitochondrial iron accumulation in a yeast frataxin-deficient strain. J Biol Chem 2002; 277:24475-83. [PMID: 12006577 DOI: 10.1074/jbc.m111789200] [Citation(s) in RCA: 146] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mitochondrial solute carriers Mrs3p and Mrs4p were originally isolated as multicopy suppressors of intron splicing defects. We show here that MRS4 is co-regulated with the iron regulon genes, and up-regulated in a strain deficient for Yfh1p, the yeast homologue of human frataxin. Using in vivo 55Fe cell radiolabeling we show that in glucose-grown cells mitochondrial iron accumulation is 5-15 times higher in deltaYFH1 than in wild-type strain. However, although in a deltaYFH1deltaMRS3deltaMRS4 strain, the intracellular 55Fe content is extremely high, the mitochondrial iron concentration is decreased to almost wild-type levels. Moreover, deltaYFH1deltaMRS3deltaMRS4 cells grown in high iron media do not lose their mitochondrial genome. Conversely, a deltaYFH1 strain overexpressing MRS4 has an increased mitochondrial iron content and no mitochondrial genome. Therefore, MRS4 is required for mitochondrial iron accumulation in deltaYFH1 cells. Expression of the iron regulon and intracellular 55Fe content are higher in a deltaMRS3deltaMRS4 strain than in the wild type. Nevertheless, the mitochondrial 55Fe content, a balance between iron uptake and exit, is decreased by a factor of two. Moreover, 55Fe incorporation into heme by ferrochelatase is increased in an MRS4-overexpressing strain. The function of MRS4 in iron import into mitochondria is discussed.
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Affiliation(s)
- Francoise Foury
- Unité de Biochimie Physiologique, Place Croix du Sud, 2-20, 1348 Louvain-la-Neuve, Belgium.
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29
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Jimeno S, Rondón A, Luna R, Aguilera A. The yeast THO complex and mRNA export factors link RNA metabolism with transcription and genome instability. EMBO J 2002; 21:3526-35. [PMID: 12093753 PMCID: PMC126085 DOI: 10.1093/emboj/cdf335] [Citation(s) in RCA: 214] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The THO complex is a multimeric factor containing four polypeptides, Tho2, Hpr1, Mft1 and Thp2. Mutations in any of the genes encoding THO confer impairment of transcription and a transcription-dependent hyper-recombination phenotype, suggesting that THO has a functional role in gene expression. Using an in vivo assay developed to study expression of long and G+C-rich DNA sequences, we have isolated SUB2, a gene involved in mRNA splicing and export, as a multicopy suppressor of the gene expression defect of hpr1 Delta. Further investigation of a putative functional relationship between mRNA metabolism and THO revealed that mRNA export mutants sub2, yra1, mex67 and mtr2 have similar defective transcription and hyper-recombination phenotypes as THO mutants. In addition, THO becomes essential in cells with a defective Mex67 mRNA export er. Finally, we have shown that THO has the ability to associate with RNA and DNA in vitro. These results indicate a functional link between the processes of elongation and metabolism of nascent mRNA mediated by THO and mRNA export proteins, which have important consequences for the maintenance of genome stability.
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Affiliation(s)
| | | | | | - A. Aguilera
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, 41012 Sevilla, Spain
Corresponding author e-mail:
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30
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Abstract
RNA folding in vivo is influenced by the cellular environment, the vectorial nature of transcription and translation, trans-acting factors and ion homeostasis. Specific RNA-binding proteins promote RNA folding by stabilizing the native structure or by guiding folding. In contrast, RNA chaperones, which are believed to interact nonspecifically with RNA, were proposed to resolve misfolded RNA structures and to promote intermolecular RNA-RNA annealing. Small trans-acting noncoding RNAs are thought to modulate mRNA structures, thereby regulating gene expression. So far, there is some evidence that in vitro and invivo RNA folding pathways share basic features. However, it is unclear whether the rules deduced from in vitro folding experiments generally apply to invivo conditions.
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Affiliation(s)
- Renée Schroeder
- Institute of Microbiology and Genetics, University of Vienna, Vienna Biocenter, Doktor Bohrgasse 9, A-1030 Vienna, Austria.
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31
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Dai L, Zimmerly S. Compilation and analysis of group II intron insertions in bacterial genomes: evidence for retroelement behavior. Nucleic Acids Res 2002; 30:1091-102. [PMID: 11861899 PMCID: PMC101233 DOI: 10.1093/nar/30.5.1091] [Citation(s) in RCA: 146] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Group II introns are novel genetic elements that have properties of both catalytic RNAs and retroelements. Initially identified in organellar genomes of plants and lower eukaryotes, group II introns are now being discovered in increasing numbers in bacterial genomes. Few of the newly sequenced bacterial introns are correctly identified or annotated by those who sequenced them. Here we have compiled and thoroughly analyzed group II introns and their fragments in bacterial DNA sequences reported to GenBank. Intron distribution in bacterial genomes differs markedly from the distribution in organellar genomes. Bacterial introns are not inserted into conserved genes, are often inserted outside of genes altogether and are frequently fragmented, suggesting a high rate of intron gain and loss. Some introns have multiple natural homing sites while others insert after transcriptional terminators. All bacterial group II introns identified to date encode reverse transcriptase open reading frames and are either active retroelements or derivatives of retroelements. Together, these observations suggest that group II introns in bacteria behave primarily as retroelements rather than as introns, and that the strategy for group II intron survival in bacteria is fundamentally different from intron survival in organelles.
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Affiliation(s)
- Lixin Dai
- Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada
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32
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Gregan J, Kolisek M, Schweyen RJ. Mitochondrial Mg(2+) homeostasis is critical for group II intron splicing in vivo. Genes Dev 2001; 15:2229-37. [PMID: 11544180 PMCID: PMC312778 DOI: 10.1101/gad.201301] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2001] [Accepted: 07/06/2001] [Indexed: 11/24/2022]
Abstract
The product of the nuclear MRS2 gene, Mrs2p, is the only candidate splicing factor essential for all group II introns in mitochondria of the yeast Saccharomyces cerevisiae. It has been shown to be an integral protein of the inner mitochondrial membrane, structurally and functionally related to the bacterial CorA Mg(2+) transporter. Here we show that mutant alleles of the MRS2 gene as well as overexpression of this gene both increase intramitochondrial Mg(2+) concentrations and compensate for splicing defects of group II introns in mit(-) mutants M1301 and B-loop. Yet, covariation of Mg(2+) concentrations and splicing is similarly seen when some other genes affecting mitochondrial Mg(2+) concentrations are overexpressed in an mrs2Delta mutant, indicating that not the Mrs2 protein per se but certain Mg(2+) concentrations are essential for group II intron splicing. This critical role of Mg(2+) concentrations for splicing is further documented by our observation that pre-mRNAs, accumulated in mitochondria isolated from mutants, efficiently undergo splicing in organello when these mitochondria are incubated in the presence of 10 mM external Mg(2+) (mit(-) M1301) and an ionophore (mrs2Delta). This finding of an exceptional sensitivity of group II intron splicing toward Mg(2+) concentrations in vivo is unprecedented and raises the question of the role of Mg(2+) in other RNA-catalyzed reactions in vivo. It explains finally why protein factors modulating Mg(2+) homeostasis had been identified in genetic screens for bona fide RNA splicing factors.
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Affiliation(s)
- J Gregan
- Vienna Biocenter, Department of Microbiology and Genetics, University of Vienna, A-1030 Vienna, Austria
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33
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Malagón F, Aguilera A. Yeast spt6-140 mutation, affecting chromatin and transcription, preferentially increases recombination in which Rad51p-mediated strand exchange is dispensable. Genetics 2001; 158:597-611. [PMID: 11404325 PMCID: PMC1461695 DOI: 10.1093/genetics/158.2.597] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have shown that the spt6-140 and spt4-3 mutations, affecting chromatin structure and transcription, stimulate recombination between inverted repeats by a RAD52-dependent mechanism that is very efficient in the absence of RAD51, RAD54, RAD55, and RAD57. Such a mechanism of recombination is RAD1-RAD59-dependent and yields gene conversions highly associated with the inversion of the repeat. The spt6-140 mutation alters transcription and chromatin in our inverted repeats, as determined by Northern and micrococcal nuclease sensitivity analyses, respectively. Hyper-recombination levels are diminished in the absence of transcription. We believe that the chromatin alteration, together with transcription impairment caused by spt6-140, increases the incidence of spontaneous recombination regardless of whether or not it is mediated by Rad51p-dependent strand exchange. Our results suggest that spt6, as well as spt4, primarily stimulates a mechanism of break-induced replication. We discuss the possibility that the chromatin alteration caused by spt6-140 facilitates a Rad52p-mediated one-ended strand invasion event, possibly inefficient in wild-type chromatin. Our results are consistent with the idea that the major mechanism leading to inversions might not be crossing over but break-induced replication followed by single-strand annealing.
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Affiliation(s)
- F Malagón
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Avd. Reina Mercedes 6, 41012 Seville, Spain
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34
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Bunse AA, Nickelsen J, Kück U. Intron-specific RNA binding proteins in the chloroplast of the green alga Chlamydomonas reinhardtii. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1519:46-54. [PMID: 11406270 DOI: 10.1016/s0167-4781(01)00211-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Mitochondria and chloroplasts both contain group II introns which are believed to be the ancestors of nuclear spliceosomal introns. We used the mitochondrial group II intron rI1 from the green alga Scenedesmus obliquus for biochemical characterization of intron-specific RNA binding proteins. rI1 is correctly spliced from a chloroplast precursor RNA when integrated into the chloroplast genome of Chlamydomonas reinhardtii. Glycerol gradients revealed the sedimentation profile of transcripts containing intron rI1 in native C. reinhardtii extracts and in deproteinized RNA preparations, thus indicating the association of rI1 containing transcripts with high molecular weight ribonucleoprotein complexes in vivo. Furthermore, the specific binding of a 61 kDa protein and a 31 kDa protein with the conserved domain IV was demonstrated using a set of intron derivatives for in vitro RNA binding experiments. We propose that we have biochemically characterized 'general splicing factors', which enable the successful splicing even of mitochondrial introns in chloroplasts.
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Affiliation(s)
- A A Bunse
- Lehrstuhl für Allgemeine und Molekulare Botanik, Fakultät für Biologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
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35
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Rivier C, Goldschmidt-Clermont M, Rochaix JD. Identification of an RNA-protein complex involved in chloroplast group II intron trans-splicing in Chlamydomonas reinhardtii. EMBO J 2001; 20:1765-73. [PMID: 11285239 PMCID: PMC145512 DOI: 10.1093/emboj/20.7.1765] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In Chlamydomonas reinhardtii, the psaA mRNA is assembled by a process involving trans-splicing of separate transcripts, encoded at three separate loci of the chloroplast genome. At least 14 nuclear loci and one chloroplast gene, tscA, are needed for this process. We have cloned Raa3, the first nuclear gene implicated in the splicing of intron 1. The predicted sequence of Raa3 consists of 1783 amino acids and shares a small region of homology with pyridoxamine 5'-phosphate oxidases. Raa3 is present in the soluble fraction of the chloroplast and is part of a large 1700 kDa complex, which also contains tscA RNA and the first psaA exon transcript. These partners, in association with other factors, form a chloroplast RNP particle that is required for the splicing of the first intron of psaA and which may be the counterpart of eukaryotic snRNPs involved in nuclear splicing.
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Affiliation(s)
| | | | - Jean-David Rochaix
- Departments of Molecular Biology and Plant Biology, University of Geneva, 30, Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland
Corresponding author e-mail:
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36
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Schock I, Gregan J, Steinhauser S, Schweyen R, Brennicke A, Knoop V. A member of a novel Arabidopsis thaliana gene family of candidate Mg2+ ion transporters complements a yeast mitochondrial group II intron-splicing mutant. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2000. [PMID: 11115130 DOI: 10.1111/j.1365-313x.2000.00895.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Autocatalytic activity of some group II introns has been demonstrated in vitro, but helper functions such as the yeast MRS2 protein are essential for splicing in vivo. In our search for such helper factors in plants, we pursued the cloning of two Arabidopsis thaliana homologues, atmrs2-1 and atmrs2-2. Atmrs2-1, but not atmrs2-2, complements the yeast deletion mutant of mrs2, and this is congruent with the prediction of two adjacent transmembrane stretches in AtMRS2-1 and yeast MRS2 but not in AtMRS2-2. This complementation depends on fusion of the native yeast mitochondrial import sequence to atmrs2-1. A differing, non-mitochondrial, cellular targeting in Arabidopsis is supported by the analysis of green fluorescent protein fusion constructs after transient transformation into plant protoplasts. Further members of what now appears to be a family of 10 mrs2 homologues are identified in the Arabidopsis genome. Similarity searches with the PSI-BLAST algorithm in the protein database fail to identify homologues of this novel gene family in any eukaryotes other than yeasts, but do identify its distant relatedness to the corA group of bacterial magnesium transporters. In line with this observation, intramitochondrial magnesium concentrations are indeed restored to wild-type levels in the yeast mutant on complementation with atmrs2-1.
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MESH Headings
- Amino Acid Sequence
- Arabidopsis/genetics
- Arabidopsis/metabolism
- Biological Transport
- Carrier Proteins/genetics
- Cloning, Molecular
- DNA, Complementary/chemistry
- DNA, Complementary/genetics
- DNA, Mitochondrial/genetics
- DNA, Plant/chemistry
- DNA, Plant/genetics
- Exons
- Genes, Plant/genetics
- Genetic Complementation Test
- Green Fluorescent Proteins
- Introns
- Ion Channels
- Luminescent Proteins/genetics
- Luminescent Proteins/metabolism
- Magnesium/metabolism
- Microscopy, Fluorescence
- Mitochondrial Proteins
- Molecular Sequence Data
- Multigene Family
- Mutation
- Nuclear Proteins/genetics
- Phylogeny
- Plants, Toxic
- Protoplasts/metabolism
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae Proteins
- Sequence Alignment
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
- Tobacco
- Transcription, Genetic
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Affiliation(s)
- I Schock
- Department of Molecular Botany, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
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37
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Contamine V, Picard M. Maintenance and integrity of the mitochondrial genome: a plethora of nuclear genes in the budding yeast. Microbiol Mol Biol Rev 2000; 64:281-315. [PMID: 10839818 PMCID: PMC98995 DOI: 10.1128/mmbr.64.2.281-315.2000] [Citation(s) in RCA: 218] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Instability of the mitochondrial genome (mtDNA) is a general problem from yeasts to humans. However, its genetic control is not well documented except in the yeast Saccharomyces cerevisiae. From the discovery, 50 years ago, of the petite mutants by Ephrussi and his coworkers, it has been shown that more than 100 nuclear genes directly or indirectly influence the fate of the rho(+) mtDNA. It is not surprising that mutations in genes involved in mtDNA metabolism (replication, repair, and recombination) can cause a complete loss of mtDNA (rho(0) petites) and/or lead to truncated forms (rho(-)) of this genome. However, most loss-of-function mutations which increase yeast mtDNA instability act indirectly: they lie in genes controlling functions as diverse as mitochondrial translation, ATP synthase, iron homeostasis, fatty acid metabolism, mitochondrial morphology, and so on. In a few cases it has been shown that gene overexpression increases the levels of petite mutants. Mutations in other genes are lethal in the absence of a functional mtDNA and thus convert this petite-positive yeast into a petite-negative form: petite cells cannot be recovered in these genetic contexts. Most of the data are explained if one assumes that the maintenance of the rho(+) genome depends on a centromere-like structure dispensable for the maintenance of rho(-) mtDNA and/or the function of mitochondrially encoded ATP synthase subunits, especially ATP6. In fact, the real challenge for the next 50 years will be to assemble the pieces of this puzzle by using yeast and to use complementary models, especially in strict aerobes.
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Affiliation(s)
- V Contamine
- Institut de Génétique et Microbiologie, UMR 8621, Université Paris-Sud, 91405 Orsay Cedex, France
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38
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Kayingo G, Potier S, Hohmann S, Prior BA. Isolation and characterization of the TIM10 homologue from the yeast Pichia sorbitophila: a putative component of the mitochondrial protein import system. Yeast 2000; 16:589-96. [PMID: 10806421 DOI: 10.1002/(sici)1097-0061(200005)16:7<589::aid-yea555>3.0.co;2-g] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
The Saccharomyces cerevisiae TIM10 gene encodes one of the few essential mitochondrial proteins that are required for the import of nuclear-encoded precursor proteins from the cytosol and their subsequent sorting into the different mitochondrial compartments. We have isolated and characterized a putative homologue of TIM10 from the halotolerant yeast Pichia sorbitophila. The Pichia TIM10 gene encodes a protein of 90 amino acids with 66% identity to S. cerevisiae Tim10p. It was capable of suppressing the temperature sensitivity of tim10-1 mutant in S. cerevisiae, suggesting that Pichia TIM10 is both a functional and structural homologue of S. cerevisiae TIM10. The putative Pichia TIM10 gene product contains all the four conserved cysteine residues and the two CX(3)C motifs typical of the Tim family proteins in the mitochondrial intermembrane space. Using anti-Tim10p serum, Western blots detected a protein of about 10 kDa, suggesting that the Pichia Tim10p is a mitochondrial protein. The results suggest that mitochondrial import and sorting systems might be also strongly conserved in other fungi. The coding sequence of the P. sorbitophila TIM10 has been deposited in the EMBL Nucleotide Sequence Database under Accession No. AJ243940.
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Affiliation(s)
- G Kayingo
- Department of Microbiology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
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39
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Koehler CM, Merchant S, Schatz G. How membrane proteins travel across the mitochondrial intermembrane space. Trends Biochem Sci 1999; 24:428-32. [PMID: 10542408 DOI: 10.1016/s0968-0004(99)01462-0] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
A newly discovered family of small proteins in the yeast mitochondrial intermembrane space mediates import of hydrophobic proteins from the cytoplasm into the inner membrane. Loss of one of these chaperone-like proteins from human mitochondria results in a disease that causes deafness, muscle weakness and blindness.
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Affiliation(s)
- C M Koehler
- Dept of Biochemistry, Biozentrum, University of Basel, CH-4056 Basel, Switzerland
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40
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Frankel A, Clarke S. RNase treatment of yeast and mammalian cell extracts affects in vitro substrate methylation by type I protein arginine N-methyltransferases. Biochem Biophys Res Commun 1999; 259:391-400. [PMID: 10362520 DOI: 10.1006/bbrc.1999.0779] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Type I protein arginine N-methyltransferases catalyze the formation of omega-NG-monomethylarginine and asymmetric omega-NG, NG-dimethylarginine residues using S-adenosyl-l-methionine as the methyl donor. In vitro these enzymes can modify a number of soluble methyl-accepting substrates in yeast and mammalian cell extracts including several species that interact with RNA. We treated normal and hypomethylated Saccharomyces cerevisiae and RAT1 cell extracts with RNase prior to in vitro methylation by recombinant protein N-arginine methyltransferases and found that the methylation of certain polypeptides is enhanced up to 12-fold whereas that of others is diminished. 2-D gel electrophoresis of RNase-treated yeast extracts allowed us to tentatively identify the glycine- and arginine-rich (GAR) domain-containing proteins Gar1, Nop1, Sbp1, and Npl3 as major methyl-acceptors based on their known isoelectric points and apparent molecular weights. These results suggest that the methylation and RNA-binding of GAR domain-containing proteins in vivo may regulate protein-nucleic acid or protein-protein interactions.
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Affiliation(s)
- A Frankel
- Department of Chemistry & Biochemistry and Molecular Biology Institute, UCLA, Los Angeles, California 90095-1569, USA
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41
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Cho JH, Ha SJ, Kao LR, Megraw TL, Chae CB. A novel DNA-binding protein bound to the mitochondrial inner membrane restores the null mutation of mitochondrial histone Abf2p in Saccharomyces cerevisiae. Mol Cell Biol 1998; 18:5712-23. [PMID: 9742088 PMCID: PMC109157 DOI: 10.1128/mcb.18.10.5712] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/1998] [Accepted: 06/23/1998] [Indexed: 11/20/2022] Open
Abstract
The yeast mitochondrial HMG-box protein, Abf2p, is essential for maintenance of the mitochondrial genome. To better understand the role of Abf2p in the maintenance of the mitochondrial chromosome, we have isolated a multicopy suppressor (YHM2) of the temperature-sensitive defect associated with an abf2 null mutation. The function of Yhm2p was characterized at the molecular level. Yhm2p has 314 amino acid residues, and the deduced amino acid sequence is similar to that of a family of mitochondrial carrier proteins. Yhm2p is localized in the mitochondrial inner membrane and is also associated with mitochondrial DNA in vivo. Yhm2p exhibits general DNA-binding activity in vitro. Thus, Yhm2p appears to be novel in that it is a membrane-bound DNA-binding protein. A sequence that is similar to the HMG DNA-binding domain is important for the DNA-binding activity of Yhm2p, and a mutation in this region abolishes the ability of YHM2 to suppress the temperature-sensitive defect of respiration of the abf2 null mutant. Disruption of YHM2 causes a significant growth defect in the presence of nonfermentable carbon sources such as glycerol and ethanol, and the cells have defects in respiration as determined by 2,3,5,-triphenyltetrazolium chloride staining. Yhm2p may function as a member of the protein machinery for the mitochondrial inner membrane attachment site of mitochondrial DNA during replication and segregation of mitochondrial genomes.
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Affiliation(s)
- J H Cho
- Department of Life Science, Pohang University of Science and Technology, Pohang 790-784, Korea
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42
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Piruat JI, Aguilera A. A novel yeast gene, THO2, is involved in RNA pol II transcription and provides new evidence for transcriptional elongation-associated recombination. EMBO J 1998; 17:4859-72. [PMID: 9707445 PMCID: PMC1170815 DOI: 10.1093/emboj/17.16.4859] [Citation(s) in RCA: 122] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have identified two novel yeast genes, THO1 and THO2, that partially suppress the transcription defects of hpr1Delta mutants by overexpression. We show by in vivo transcriptional and recombinational analysis of tho2Delta cells that THO2 plays a role in RNA polymerase II (RNA pol II)-dependent transcription and is required for the stability of DNA repeats, as previously shown for HPR1. The tho2Delta mutation reduces the transcriptional efficiency of yeast DNA sequences down to 25% of the wild-type levels and abolishes transcription of the lacZ sequence. In addition, tho2Delta causes a strong increase in the frequency of recombination between direct repeats (>2000-fold above wild-type levels). Some DNA repeats cannot even be maintained in the cell. This hyper-recombination phenotype is dependent on transcription and is not observed in DNA repeats that are not transcribed. The higher the impairment of transcription caused by tho2Delta, the higher the frequency of recombination of a particular DNA region. The tho2Delta mutation also increases the frequency of plasmid loss. Our work not only identifies a novel yeast gene, THO2, with similar function to HPR1, but also provides new evidence for transcriptional blocks as a source of recombination. We propose that there is a set of proteins including Hpr1p and Tho2p, in the absence of which RNA pol II transcription is stalled or blocked, causing genetic instability.
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Affiliation(s)
- J I Piruat
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, E-41012 Sevilla, Spain
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43
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Qin PZ, Pyle AM. The architectural organization and mechanistic function of group II intron structural elements. Curr Opin Struct Biol 1998; 8:301-8. [PMID: 9666325 DOI: 10.1016/s0959-440x(98)80062-6] [Citation(s) in RCA: 116] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Group II introns are large, self-splicing RNAs and mobile genetic elements that provide good model systems for studies of RNA folding. The structures and mechanistic functions of individual domains are being elucidated, and long-range tertiary interactions between the domains are being identified, thus helping to define the three-dimensional architecture of the intron.
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Affiliation(s)
- P Z Qin
- Howard Hughes Medical Institute, Department of Applied Physics, New York, NY 10032, USA
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44
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Sirrenberg C, Endres M, Fölsch H, Stuart RA, Neupert W, Brunner M. Carrier protein import into mitochondria mediated by the intermembrane proteins Tim10/Mrs11 and Tim12/Mrs5. Nature 1998; 391:912-5. [PMID: 9495346 DOI: 10.1038/36136] [Citation(s) in RCA: 241] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Import of nuclear-encoded precursor proteins into mitochondria and their subsequent sorting into mitochondrial subcompartments is mediated by translocase enzymes in the mitochondrial outer and inner membranes. Precursor proteins carrying amino-terminal targeting signals are translocated into the matrix by the integral inner membrane proteins Tim23 and Tim17 in cooperation with Tim44 and mitochondrial Hsp70. We describe here the discovery of a new pathway for the transport of members of the mitochondrial carrier family and other inner membrane proteins that contain internal targeting signals. Two related proteins in the intermembrane space, Tim10/Mrs11 and Tim12/Mrs5, interact sequentially with these precursors and facilitate their translocation across the outer membrane, irrespective of the membrane potential. Tim10 and Tim12 are found in a complex with Tim22, which takes over the precursor and mediates its membrane-potential-dependent insertion into the inner membrane. This interaction of Tim10 and Tim12 with the precursors depends on the presence of divalent metal ions. Both proteins contain a zinc-finger-like motif with four cysteines and bind equimolar amounts of zinc ions.
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Affiliation(s)
- C Sirrenberg
- Institut für Physiologische Chemie der Universität München, Germany
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45
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Koehler CM, Jarosch E, Tokatlidis K, Schmid K, Schweyen RJ, Schatz G. Import of mitochondrial carriers mediated by essential proteins of the intermembrane space. Science 1998; 279:369-73. [PMID: 9430585 DOI: 10.1126/science.279.5349.369] [Citation(s) in RCA: 251] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
In order to reach the inner membrane of the mitochondrion, multispanning carrier proteins must cross the aqueous intermembrane space. Two essential proteins of that space, Tim10p and Tim12p, were shown to mediate import of multispanning carriers into the inner membrane. Both proteins formed a complex with the inner membrane protein Tim22p. Tim10p readily dissociated from the complex and was required to transport carrier precursors across the outer membrane; Tim12p was firmly bound to Tim22p and mediated the insertion of carriers into the inner membrane. Neither protein was required for protein import into the other mitochondrial compartments. Both proteins may function as intermembrane space chaperones for the highly insoluble carrier proteins.
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Affiliation(s)
- C M Koehler
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
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46
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Bauer BE, Lorenzetti S, Miaczynska M, Bui DM, Schweyen RJ, Ragnini A. Amino- and carboxy-terminal domains of the yeast Rab escort protein are both required for binding of Ypt small G proteins. Mol Biol Cell 1996; 7:1521-33. [PMID: 8898359 PMCID: PMC276003 DOI: 10.1091/mbc.7.10.1521] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The Rab escort protein (REP) is an essential component of the heterotrimeric enzyme Rab geranylgeranyl transferase that modifies the carboxy-terminal cysteines of the Ras-like small G proteins belonging to the Rab/Ypt family. Deletions in the human CHM locus, encoding one of the two REPs known in humans, result in a retinal degenerative syndrome called choroideremia. The only known yeast homologue of the choroideremia gene product is encoded by an essential gene called MRS6. Besides three structurally conserved regions (SCRs) previously detected in the amino-terminal half of REPs and RabGDIs, three other regions in the carboxy-terminal domain (RCR 1-3) are here identified as being characteristic of REPs alone. We have performed the first mutational analysis of a REP protein to experimentally define the regions functionally important for Rab/Ypt protein binding, making use of the genetic system of the yeast Saccharomyces cerevisiae. This analysis has shown that the SCRs are necessary but not sufficient for Ypt1p binding by the yeast REP, the carboxy-terminal region also being required.
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Affiliation(s)
- B E Bauer
- Vienna Biocenter, University of Vienna, Austria
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47
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Jarosch E, Tuller G, Daum G, Waldherr M, Voskova A, Schweyen RJ. Mrs5p, an essential protein of the mitochondrial intermembrane space, affects protein import into yeast mitochondria. J Biol Chem 1996; 271:17219-25. [PMID: 8663351 DOI: 10.1074/jbc.271.29.17219] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
We have isolated a yeast nuclear gene that suppresses the previously described respiration-deficient mrs2-1 mutation when present on a multicopy plasmid. Elevated gene dosage of this new gene, termed MRS5, suppresses also the pet phenotype of a mitochondrial splicing-deficient group II intron mutation M1301. The MRS5 gene product, a 13-kDa protein of low abundance, shows no similarity to other known proteins and is associated with the inner mitochondrial membrane, protruding into the intermembrane space. MRS5 codes for an essential protein, as the disruption of this gene is lethal even during growth on fermentable carbon sources. Thus, the Mrs5 protein seems to be involved in mitochondrial key functions aside from oxidative energy conservation, which is dispensable in fermenting yeast cells. Depletion of Mrs5p in yeast cells causes accumulation of unprocessed precursors of the mitochondrial hsp60 protein and defects in all cytochrome complexes. These findings suggest an essential role of Mrs5p in mitochondrial biogenesis.
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Affiliation(s)
- E Jarosch
- Institut für Mikrobiologie und Genetik, Universität Wien, A-1030 Vienna, Austria
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48
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Herrera-Camacho I, Suárez-Rendueles P. Regulation of the yeast vacuolar aminopeptidase Y gene (APY1) expression. FEMS Microbiol Lett 1996; 139:127-32. [PMID: 8674980 DOI: 10.1111/j.1574-6968.1996.tb08191.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The steady-state levels of the aminopeptidase Y (APY1) transcript and the level of assayable aminopeptidase Y activity were measured under a variety of nutritional conditions. Specific APY1 mRNA is less abundant in cells grown in minimal medium than in cells grown in rich medium, while active enzyme levels follow just the opposite pattern. Aminopeptidase Y activity decreases when cells are deprived of glucose without a concomitant fall in mRNA levels. Production of aminopeptidase Y is not markedly affected by nitrogen regulation. APY1 gene expression is not disturbed in heat-shocked cells. Our data support the idea that the main control event in vacuolar aminopeptidase Y expression is a post-transcriptional step.
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Affiliation(s)
- I Herrera-Camacho
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo, Spain
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49
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50
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Van Dyck E, Jank B, Ragnini A, Schweyen RJ, Duyckaerts C, Sluse F, Foury F. Overexpression of a novel member of the mitochondrial carrier family rescues defects in both DNA and RNA metabolism in yeast mitochondria. MOLECULAR & GENERAL GENETICS : MGG 1995; 246:426-36. [PMID: 7891656 DOI: 10.1007/bf00290446] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The PIF1 and MRS2 gene products have previously been shown to be essential for mitochondrial DNA maintenance at elevated temperatures and mitochondrial group II intron splicing, respectively, in the yeast Saccharomyces cerevisiae. A multicopy suppressor capable of rescuing the respiratory deficient phenotype associated with null alleles of either gene has been isolated. This suppressor is a nuclear gene that was called RIM2/MRS12. The RIM2/MRS12 gene encodes a predicted protein of 377 amino acids that is essential for mitochondrial DNA metabolism and proper cell growth. Inactivation of this gene causes the total loss of mitochondrial DNA and, compared to wild-type rhoo controls, a slow-growth phenotype on media containing glucose. Analysis of the RIM2/MRS12 protein sequence suggests that RIM2/MRS12 encodes a novel member of the mitochondrial carrier family. In particular, a typical triplicate structure, where each repeat consists of two putative transmembrane segments separated by a hydrophilic loop, can be deduced from amino acid sequence comparisons and the hydropathy profile of RIM2/MRS12. Antibodies directed against the aminoterminus of RIM2/MRS12 detect this protein in mitochondria. The function of the RIM2/MRS12 protein and the substrates it might transport are discussed.
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Affiliation(s)
- E Van Dyck
- Unité de Biochimie Physiologique, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
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