scholarly journals Functional interactions among two yeast mitochondrial ribosomal proteins and an mRNA-specific translational activator.

Genetics ◽  
1991 ◽  
Vol 127 (2) ◽  
pp. 319-326
Author(s):  
P Haffter ◽  
T W McMullin ◽  
T D Fox
Keyword(s):  
Ribosomal Proteins ◽  
Mitochondrial Gene ◽  
Nuclear Gene ◽  
Small Subunit ◽  
Mitochondrial Ribosomes ◽  
Gene Coding ◽  
Allele Specific ◽  
Carboxyl Terminal ◽  
Translational Activator ◽  
Carboxy Terminal

Abstract Expression of the Saccharomyces cerevisiae mitochondrial gene coding cytochrome c oxidase subunit III is specifically activated at the level of translation by at least three nuclear genes, PET122, PET494 and PET54. We have shown previously that carboxy-terminal deletions of PET122 are allele-specifically suppressed by mutations in an unlinked nuclear gene, termed PET123, that encodes a small subunit ribosomal protein. Here we describe additional pet122 suppressors generated by mutations in a second gene which we show to be the previously identified nuclear gene MRP1. Like PET123, MRP1 encodes a component of the small subunit of mitochondrial ribosomes. Our mrp1 mutations are allele-specific suppressors of carboxyl-terminal truncations of the PET122 protein and do not bypass the requirement for residual function of PET122. None of our mrp1 mutations has an intrinsic phenotype in an otherwise wild-type background. However, some of the mrp1 mutations cause a non-conditional respiratory-defective phenotype in combination with certain pet123 alleles. This synthetic defective phenotype suggests that the ribosomal proteins PET123 and MRP1 interact functionally with each other. The fact that they can both mutate to suppress certain alleles of the mRNA-specific translational activator PET122 strongly suggests that the PET122 protein promotes translation of the coxIII mRNA via an interaction with the small subunit of mitochondrial ribosomes.

scholarly journals A novel small-subunit ribosomal protein of yeast mitochondria that interacts functionally with an mRNA-specific translational activator.

1990 ◽  
Vol 10 (9) ◽  
pp. 4590-4595 ◽  
Author(s):  
T W McMullin ◽  
P Haffter ◽  
T D Fox
Keyword(s):  
Ribosomal Protein ◽  
Ribosomal Proteins ◽  
Mitochondrial Gene ◽  
Ribosomal Subunit ◽  
Nuclear Gene ◽  
Small Subunit ◽  
Rrna Gene ◽  
Mitochondrial Translation ◽  
Activator Proteins ◽  
Translational Activator

Mitochondrial translation of the mRNA encoding cytochrome c oxidase subunit III (coxIII) specifically requires the action of three position activator proteins encoded in the nucleus of Saccharomyces cerevisiae. Some mutations affecting one of these activators, PET122, can be suppressed by mutations in an unlinked nuclear gene termed PET123. PET123 function was previously demonstrated to be required for translation of all mitochondrial gene products. We have now generated an antibody against the PET123 protein and have used it to demonstrate that PET123 is a mitochondrial ribosomal protein of the small subunit. PET123 appears to be present at levels comparable to those of other mitochondrial ribosomal proteins, and its accumulation is dependent on the presence of the 15S rRNA gene in mitochondria. Taken together with the previous genetic data, these results strongly support a model in which the mRNA-specific translational activator PET122 works by directly interacting with the small ribosomal subunit to promote translation initiation on the coxIII mRNA.

A novel small-subunit ribosomal protein of yeast mitochondria that interacts functionally with an mRNA-specific translational activator

1990 ◽  
Vol 10 (9) ◽  
pp. 4590-4595
Author(s):  
T W McMullin ◽  
P Haffter ◽  
T D Fox
Keyword(s):  
Ribosomal Protein ◽  
Ribosomal Proteins ◽  
Mitochondrial Gene ◽  
Ribosomal Subunit ◽  
Nuclear Gene ◽  
Small Subunit ◽  
Rrna Gene ◽  
Mitochondrial Translation ◽  
Activator Proteins ◽  
Translational Activator

Mitochondrial translation of the mRNA encoding cytochrome c oxidase subunit III (coxIII) specifically requires the action of three position activator proteins encoded in the nucleus of Saccharomyces cerevisiae. Some mutations affecting one of these activators, PET122, can be suppressed by mutations in an unlinked nuclear gene termed PET123. PET123 function was previously demonstrated to be required for translation of all mitochondrial gene products. We have now generated an antibody against the PET123 protein and have used it to demonstrate that PET123 is a mitochondrial ribosomal protein of the small subunit. PET123 appears to be present at levels comparable to those of other mitochondrial ribosomal proteins, and its accumulation is dependent on the presence of the 15S rRNA gene in mitochondria. Taken together with the previous genetic data, these results strongly support a model in which the mRNA-specific translational activator PET122 works by directly interacting with the small ribosomal subunit to promote translation initiation on the coxIII mRNA.

scholarly journals The translational activator Sov1 coordinates mitochondrial gene expression with mitoribosome biogenesis

2020 ◽  
Vol 48 (12) ◽  
pp. 6759-6774 ◽  
Author(s):  
Suhas R Seshadri ◽  
Chitra Banarjee ◽  
Mario H Barros ◽  
Flavia Fontanesi
Keyword(s):  
Gene Expression ◽  
Functional Role ◽  
Regulatory Mechanism ◽  
Mitochondrial Gene ◽  
Small Subunit ◽  
Metabolic Process ◽  
Mitochondrial Gene Expression ◽  
Var1 Gene ◽  
Bona Fide ◽  
Translational Activator

Abstract Mitoribosome biogenesis is an expensive metabolic process that is essential to maintain cellular respiratory capacity and requires the stoichiometric accumulation of rRNAs and proteins encoded in two distinct genomes. In yeast, the ribosomal protein Var1, alias uS3m, is mitochondrion-encoded. uS3m is a protein universally present in all ribosomes, where it forms part of the small subunit (SSU) mRNA entry channel and plays a pivotal role in ribosome loading onto the mRNA. However, despite its critical functional role, very little is known concerning VAR1 gene expression. Here, we demonstrate that the protein Sov1 is an in bona fide VAR1 mRNA translational activator and additionally interacts with newly synthesized Var1 polypeptide. Moreover, we show that Sov1 assists the late steps of mtSSU biogenesis involving the incorporation of Var1, an event necessary for uS14 and mS46 assembly. Notably, we have uncovered a translational regulatory mechanism by which Sov1 fine-tunes Var1 synthesis with its assembly into the mitoribosome.

scholarly journals Alteration of a Novel Dispensable Mitochondrial Ribosomal Small-Subunit Protein, Rsm28p, Allows Translation of Defective COX2 mRNAs

2005 ◽  
Vol 4 (2) ◽  
pp. 337-345 ◽  
Author(s):  
Elizabeth H. Williams ◽  
Nada Bsat ◽  
Nathalie Bonnefoy ◽  
Christine A. Butler ◽  
Thomas D. Fox
Keyword(s):  
Mitochondrial Gene ◽  
Carbon Sources ◽  
Small Subunit ◽  
Wild Type ◽  
Inner Mitochondrial Membrane ◽  
Positive Role ◽  
Mitochondrial Ribosomes ◽  
The Matrix ◽  
Triton X ◽  
Type Strains

ABSTRACT Mutations affecting the RNA sequence of the first 10 codons of the Saccharomyces cerevisiae mitochondrial gene COX2 strongly reduce translation of the mRNA, which encodes the precursor of cytochrome c oxidase subunit II. A dominant chromosomal mutation that suppresses these defects is an internal in-frame deletion of 67 codons from the gene YDR494w. Wild-type YDR494w encodes a 361-residue polypeptide with no similarity to proteins of known function. The epitope-tagged product of this gene, now named RSM28, is both peripherally associated with the inner surface of the inner mitochondrial membrane and soluble in the matrix. Epitope-tagged Rsm28p from Triton X-100-solubilized mitochondria sedimented with the small subunit of mitochondrial ribosomes in a sucrose gradient containing 500 mM NH4Cl. Complete deletion of RSM28 caused only a modest decrease in growth on nonfermentable carbon sources in otherwise wild-type strains and enhanced the respiratory defect of the suppressible cox2 mutations. The rsm28 null mutation also reduced translation of an ARG8 m reporter sequence inserted at the COX1, COX2, and COX3 mitochondrial loci. We tested the ability of RSM28-1 to suppress a variety of cox2 and cox3 mutations and found that initiation codon mutations in both genes were suppressed. We conclude that Rsm28p is a dispensable small-subunit mitochondrial ribosomal protein previously undetected in systematic investigations of these ribosomes, with a positive role in translation of several mitochondrial mRNAs.

scholarly journals Structure of the mature kinetoplastids mitoribosome and insights into its large subunit biogenesis

2020 ◽  
Vol 117 (47) ◽  
pp. 29851-29861 ◽  
Author(s):  
Heddy Soufari ◽  
Florent Waltz ◽  
Camila Parrot ◽  
Stéphanie Durrieu-Gaillard ◽  
Anthony Bochler ◽  
...  
Keyword(s):  
Ribosomal Proteins ◽  
Large Subunit ◽  
Microscopy Study ◽  
Small Subunit ◽  
Electron Microscopy Study ◽  
Mitochondrial Ribosomes ◽  
Cryo Electron Microscopy ◽  
Parasite Survival ◽  
Assembly Intermediate ◽  
Early Translation

Kinetoplastids are unicellular eukaryotic parasites responsible for such human pathologies as Chagas disease, sleeping sickness, and leishmaniasis. They have a single large mitochondrion, essential for the parasite survival. In kinetoplastid mitochondria, most of the molecular machineries and gene expression processes have significantly diverged and specialized, with an extreme example being their mitochondrial ribosomes. These large complexes are in charge of translating the few essential mRNAs encoded by mitochondrial genomes. Structural studies performed inTrypanosoma bruceialready highlighted the numerous peculiarities of these mitoribosomes and the maturation of their small subunit. However, several important aspects mainly related to the large subunit (LSU) remain elusive, such as the structure and maturation of its ribosomal RNA. Here we present a cryo-electron microscopy study of the protozoansLeishmania tarentolaeandTrypanosoma cruzimitoribosomes. For both species, we obtained the structure of their mature mitoribosomes, complete rRNA of the LSU, as well as previously unidentified ribosomal proteins. In addition, we introduce the structure of an LSU assembly intermediate in the presence of 16 identified maturation factors. These maturation factors act on both the intersubunit and the solvent sides of the LSU, where they refold and chemically modify the rRNA and prevent early translation before full maturation of the LSU.

scholarly journals The human mitochondrial 12S rRNA m4C methyltransferase METTL15 is required for mitochondrial function

2020 ◽  
Vol 295 (25) ◽  
pp. 8505-8513 ◽  
Author(s):  
Hao Chen ◽  
Zhennan Shi ◽  
Jiaojiao Guo ◽  
Kao-jung Chang ◽  
Qianqian Chen ◽  
...  
Keyword(s):  
Mitochondrial Function ◽  
Mitochondrial Protein ◽  
Nuclear Gene ◽  
Small Subunit ◽  
12S Rrna ◽  
Mitochondrial Rna ◽  
Small Subunit Rrna ◽  
Mitochondrial Ribosomes

Mitochondrial DNA gene expression is coordinately regulated both pre- and post-transcriptionally, and its perturbation can lead to human pathologies. Mitochondrial rRNAs (mt-rRNAs) undergo a series of nucleotide modifications after release from polycistronic mitochondrial RNA precursors, which is essential for mitochondrial ribosomal biogenesis. Cytosine N4-methylation (m4C) at position 839 (m4C839) of the 12S small subunit mt-rRNA was identified decades ago; however, its biogenesis and function have not been elucidated in detail. Here, using several approaches, including immunofluorescence, RNA immunoprecipitation and methylation assays, and bisulfite mapping, we demonstrate that human methyltransferase-like 15 (METTL15), encoded by a nuclear gene, is responsible for 12S mt-rRNA methylation at m4C839 both in vivo and in vitro. We tracked the evolutionary history of RNA m4C methyltransferases and identified a difference in substrate preference between METTL15 and its bacterial ortholog rsmH. Additionally, unlike the very modest impact of a loss of m4C methylation in bacterial small subunit rRNA on the ribosome, we found that METTL15 depletion results in impaired translation of mitochondrial protein-coding mRNAs and decreases mitochondrial respiration capacity. Our findings reveal that human METTL15 is required for mitochondrial function, delineate the evolution of methyltransferase substrate specificities and modification patterns in rRNA, and highlight a differential impact of m4C methylation on prokaryotic ribosomes and eukaryotic mitochondrial ribosomes.

scholarly journals An Update on Mitochondrial Ribosome Biology: The Plant Mitoribosome in the Spotlight

Cells ◽  
2019 ◽  
Vol 8 (12) ◽  
pp. 1562 ◽  
Author(s):  
Artur Tomal ◽  
Malgorzata Kwasniak-Owczarek ◽  
Hanna Janska
Keyword(s):  
Structural Information ◽  
Mitochondrial Gene ◽  
Protein Composition ◽  
Small Subunit ◽  
Mitochondrial Gene Expression ◽  
Mitochondrial Ribosomes ◽  
Composition And Structure ◽  
Mitochondrial Ribosome ◽  
Different Types ◽  
Convincing Data

Contrary to the widely held belief that mitochondrial ribosomes (mitoribosomes) are highly similar to bacterial ones, recent experimental evidence reveals that mitoribosomes do differ significantly from their bacterial counterparts. This review is focused on plant mitoribosomes, but we also highlight the most striking similarities and differences between the plant and non-plant mitoribosomes. An analysis of the composition and structure of mitoribosomes in trypanosomes, yeast, mammals and plants uncovers numerous organism-specific features. For the plant mitoribosome, the most striking feature is the enormous size of the small subunit compared to the large one. Apart from the new structural information, possible functional peculiarities of different types of mitoribosomes are also discussed. Studies suggest that the protein composition of mitoribosomes is dynamic, especially during development, giving rise to a heterogeneous populations of ribosomes fulfilling specific functions. Moreover, convincing data shows that mitoribosomes interact with components involved in diverse mitochondrial gene expression steps, forming large expressosome-like structures.

scholarly journals Aep3p-dependent translation of yeast mitochondrial ATP8

2017 ◽  
Vol 28 (11) ◽  
pp. 1426-1434 ◽  
Author(s):  
Mario H. Barros ◽  
Alexander Tzagoloff
Keyword(s):  
Mitochondrial Gene ◽  
Nuclear Gene ◽  
Untranslated Regions ◽  
Temperature Sensitive ◽  
Permissive Temperature ◽  
Gene Products ◽  
Expression Plasmid ◽  
Mitochondrial Ribosomes ◽  
Recessive Mutations ◽  
Initiation Of Translation

Translation of mitochondrial gene products in Saccharomyces cerevisiae depends on mRNA-specific activators that bind to the 5’ untranslated regions and promote translation on mitochondrial ribosomes. Here we find that Aep3p, previously shown to stabilize the bicistronic ATP8-ATP6 mRNA and facilitate initiation of translation from unformylated methionine, also activates specifically translation of ATP8. This is supported by several lines of evidence. Temperature-sensitive aep3 mutants are selectively blocked in incorporating [35S]methionine into Atp8p at nonpermissive but not at the permissive temperature. This phenotype is not a consequence of defective transcription or processing of the pre-mRNA. Neither is it explained by turnover of Aep3p, as evidenced by the failure of aep3 mutants to express a recoded ARG8m when this normally nuclear gene is substituted for ATP8 in mitochondrial DNA. Finally, translational of ATP8 mRNA in aep3 mutants is partially rescued by recoded allotopic ATP8 (nATP8) in a high-expression plasmid or in a CEN plasmid in the presence of recessive mutations in genes involved in stability and polyadenylation of RNA.

scholarly journals Functional Interactions between Yeast Mitochondrial Ribosomes and mRNA 5′ Untranslated Leaders

1998 ◽  
Vol 18 (4) ◽  
pp. 1826-1834 ◽  
Author(s):  
Noelle S. Green-Willms ◽  
Thomas D. Fox ◽  
Maria C. Costanzo
Keyword(s):  
Mitochondrial Gene ◽  
Small Subunit ◽  
Initiation Codon ◽  
Translational Efficiency ◽  
General Function ◽  
E Coli ◽  
Mitochondrial Ribosomes ◽  
Suppressor Mutations ◽  
Translational Activation ◽  
Untranslated Leaders

ABSTRACT Translation of mitochondrial mRNAs in Saccharomyces cerevisiae depends on mRNA-specific translational activators that recognize the 5′ untranslated leaders (5′-UTLs) of their target mRNAs. We have identified mutations in two new nuclear genes that suppress translation defects due to certain alterations in the 5′-UTLs of both the COX2 and COX3 mRNAs, indicating a general function in translational activation. One gene, MRP21, encodes a protein with a domain related to the bacterial ribosomal protein S21 and to unidentified proteins of several animals. The other gene, MRP51, encodes a novel protein whose only known homolog is encoded by an unidentified gene in S. kluyveri. Deletion of either MRP21 or MRP51 completely blocked mitochondrial gene expression. Submitochondrial fractionation showed that both Mrp21p and Mrp51p cosediment with the mitochondrial ribosomal small subunit. The suppressor mutations are missense substitutions, and those affecting Mrp21p alter the region homologous to E. coli S21, which is known to interact with mRNAs. Interactions of the suppressor mutations with leaky mitochondrial initiation codon mutations strongly suggest that the suppressors do not generally increase translational efficiency, since some alleles that strongly suppress 5′-UTL mutations fail to suppress initiation codon mutations. We propose that mitochondrial ribosomes themselves recognize a common feature of mRNA 5′-UTLs which, in conjunction with mRNA-specific translational activation, is required for organellar translation initiation.

scholarly journals Structure of the full kinetoplastids mitoribosome and insight on its large subunit maturation

2020 ◽  
Author(s):  
Heddy Soufari ◽  
Florent Waltz ◽  
Camila Parrot ◽  
Stéphanie Durrieu ◽  
Anthony Bochler ◽  
...  
Keyword(s):  
Ribosomal Proteins ◽  
Large Subunit ◽  
Microscopy Study ◽  
Small Subunit ◽  
Electron Microscopy Study ◽  
Mitochondrial Ribosomes ◽  
Cryo Electron Microscopy ◽  
Parasite Survival ◽  
Assembly Intermediate ◽  
Early Translation

AbstractKinetoplastids are unicellular eukaryotic parasites responsible for human pathologies such as Chagas disease, sleeping sickness or Leishmaniasis1. They possess a single large mitochondrion, essential for the parasite survival2. In kinetoplastids mitochondrion, most of the molecular machineries and gene expression processes have significantly diverged and specialized, with an extreme example being their mitochondrial ribosomes3. These large complexes are in charge of translating the few essential mRNAs encoded by mitochondrial genomes4,5. Structural studies performed in Trypanosoma brucei already highlighted the numerous peculiarities of these mitoribosomes and the maturation of their small subunit3,6. However, several important aspects mainly related to the large subunit remain elusive, such as the structure and maturation of its ribosomal RNA3. Here, we present a cryo-electron microscopy study of the protozoans Leishmania tarentolae and Trypanosoma cruzi mitoribosomes. For both species, we obtained the structure of their mature mitoribosomes, complete rRNA of the large subunit as well as previously unidentified ribosomal proteins. Most importantly, we introduce the structure of an LSU assembly intermediate in presence of 16 identified maturation factors. These maturation factors act both on the intersubunit and solvent sides of the LSU, where they refold and chemically modify the rRNA and prevent early translation before full maturation of the LSU.

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