Translational activators align mitochondrial mRNAs at the small ribosomal subunit for translation initiation
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PROVIDER: PRJNA1191052 | ENA |
REPOSITORIES: ENA
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Project description:Mitochondrial gene expression is essential for oxidative phosphorylation. Mitochondrial-encoded mRNAs are translated by dedicated mitochondrial ribosomes (mitoribosomes), whose regulation remains elusive. In the baker´s yeast Saccharomyces cerevisiae, nuclear-encoded mitochondrial translational activators (TAs) facilitate transcript-specific translation by a yet unknown mechanism. Here, we investigated the function of TAs containing RNA-binding pentatricopeptide repeats (PPRs) using selective mitoribosome profiling and cryo-EM structural analysis. These analyses revealed that TAs exhibit strong selectivity for mitoribosomes initiating on their target transcripts. Moreover, TA-mitoribosome footprints indicated that TAs recruit mitoribosomes proximal to the start codon. Two cryo-EM structures of mRNA-TA complexes bound to post-initiation/pre-elongation-stalled mitoribosomes revealed the general mechanism of TA action. Specifically, the TAs bind to structural elements in the 5' UTR of the client mRNA as well as to the mRNA exit channel to align the mRNA in the small subunit during initiation. Our findings provide a structural basis for understanding how mitochondria achieve transcript-specific translation initiation without relying on general sequence elements to position ribosomes at start codons.
2025-07-16 | GSE282943 | GEO
Project description:The PI3K-Akt-mTOR signaling pathway is a master regulator of RNA translation. Pharmacological inhibition of this pathway preferentially and coordinately suppresses, in a 4EBP1/2-dependent manner, translation of mRNAs encoding ribosomal proteins. However, it remains unclear whether mTOR-4EBP1/2 is the exclusive translational regulator of this group of genes, and furthermore, systematic searches for novel translational modulators have been immensely challenging due to difficulties in scaling existing RNA translation profiling assays. Here, we developed a rapid and highly scalable approach for gene-specific quantitation of RNA translation, termed Targeted Profiling of RNA Translation (TPRT). We applied this technique in a chemical screen for novel translational modulators, and identified numerous preclinical and clinical therapeutic compounds, with diverse nominal targets, that preferentially suppress translation of ribosomal proteins. Surprisingly, some of these compounds act in a manner that bypasses canonical regulation by mTOR-4EBP1/2. Instead, these compounds exert their translational effects in a manner that is dependent upon GCN2-eIF2α, a central signaling axis within the integrated stress response. Furthermore, we were also able to identify metabolic perturbations that also suppress ribosomal protein translation in an mTOR-independent manner. Together, we describe a novel translational assay that is directly applicable to large-scale RNA translation studies, and that enabled us to identify a non-canonical, mTOR-independent mode for translational regulation of ribosomal proteins.
2018-09-21 | GSE118422 | GEO
Project description:These are the ribosomal subunit fractions from the polysome gradients. investigating effect of heat shock on procyclic-form trypanosomes.
2022-01-22 | E-MTAB-11314 | biostudies-arrayexpress
Project description:Tau drives translational selectivity by interacting with ribosomal proteins
| PRJNA496504 | ENA
Project description:Structural basis of ribosomal 30S subunit degradation by RNase R
| PRJNA1055080 | ENA
Project description:Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disorder, caused by an unstable CAG-repeat expansion in the SCA2 gene, which encodes a polyglutamine (polyQ) domain expansion in the protein ataxin-2 (ATXN2). The RNA-binding protein ATXN2 interacts with the poly(A)-binding protein PABPC1, localizing to ribosomes in the rough endoplasmic reticulum or in polysomes. Under cell stress ATXN2 and PABPC1 are relocated to stress granules where mRNAs are protected from translation and from degradation. It is unknown whether ATXN2 associates preferentially with specific mRNAs or how it modulates their processing. Here, we investigated the RNA profile of liver and cerebellum from adult Atxn2 knock-out (Atxn2-/-) mice, employing oligonucleotide microarrays for screening and RNA deep sequencing for validation. We consistently observed modest upregulations for the level of many mRNAs encoding proteins of the ribosomal large and small subunit as well as the translation initiation complex. Quantitative reverse transcriptase PCR in liver tissue confirmed these upregulations for the ribosomal components Rpl14, Rpl18, Rps10, Rps18, Gnb2l1, the translation initiation factors Eif2s2, Eif3s6, Pabpc1, and the ribosomal biogenesis modulator Nop10. Quantitative immunoblots substantiated the effects for PABPC1. Thus, the physiological role of ATXN2 modifies the abundance of cellular translation factors.
2017-05-27 | GSE57998 | GEO
Project description:The integrated stress response (ISR) is a central signalling network that enables eukaryotic cells to respond to a variety of different environmental stresses. Such stresses cause ribosome collisions that lead to activation of the kinase Gcn2, resulting in the phosphorylation and inactivation of eukaryotic initiation factor 2 and thereby promoting selective translation of mRNAs to restore homeostasis. Despite the importance of the ISR and intensive study over the past decades, structural insight into how Gcn2 interacts with ribosomal particles has been lacking. Using ex vivo affinity purification approaches, we have obtained a native structure of a Gcn2 dimer in complex with the ribosomal 60S subunit. The Gcn2 dimer is formed by dimerization of the histidine tRNA synthetase-like domains, which establish extensive interactions with the stalk-base and sarcin-ricin loop of the 60S subunit. The C-terminal domain of Gcn2 is also dimerized and occupies the A- and P-site tRNA binding sites at the peptidyl-transferase center of the 60S subunit. Complementary functional studies indicate that binding of Gcn2 to the 60S subunit does not require the co-activators Gcn1 or Gcn20, nor does it lead to phosphorylation of eIF2a. Rather, upon stress, we observe a shift of Gcn2 from the 60S subunit into the colliding ribosome fraction, suggesting that the Gcn2-60S complex represents an inactive stand-by state to enable a rapid redistribution to collided ribosomes, and thereby facilitating a quick and efficient response to stress.
2024-09-16 | PXD055898 | Pride
Project description:Mammalian mitochondrial translational initiation factor 3 (IF3(mt)) binds to the small subunit of the ribosome displacing the large subunit during the initiation of protein biosynthesis. About half of the proteins in mitochondrial ribosomes have homologs in bacteria while the remainder are unique to the mitochondrion. To obtain information on the ribosomal proteins located near the IF3(mt) binding site, cross-linking studies were carried out followed by identification of the cross-linked proteins by mass spectrometry. IF3(mt) cross-links to mammalian mitochondrial homologs of the bacterial ribosomal proteins S5, S9, S10, and S18-2 and to unique mitochondrial ribosomal proteins MRPS29, MRPS32, MRPS36 and PTCD3 (Pet309) which has now been identified as a small subunit ribosomal protein. IF3(mt) has extensions on both the N- and C-termini compared to the bacterial factors. Cross-linking of a truncated derivative lacking these extensions gives the same hits as the full length IF3(mt) except that no cross-links were observed to MRPS36. IF3 consists of two domains separated by a flexible linker. Cross-linking of the isolated N- and C-domains was observed to a range of ribosomal proteins particularly with the C-domain carrying the linker which showed significant cross-linking to several ribosomal proteins not found in prokaryotes.
| S-EPMC3223260 | biostudies-literature
Project description:To assess the influence of degenerate initiation triplets on mRNA recruitment by ribosomes, five mRNAs identical but for their start codon (AUG, GUG, UUG, AUU and AUA) were offered to a limiting amount of ribosomes, alone or in competition with an identical AUGmRNA bearing a mutation conferring different electrophoretic mobility to the product. Translational efficiency and competitiveness of test mRNAs toward this AUGmRNA were determined quantifying the relative amounts of the electrophoretically separated wt and mutated products synthesized in vitro and found to be influenced to different extents by the nature of their initiation triplet and by parameters such as temperature and nutrient availability in the medium. The behaviors of AUAmRNA, UUGmRNA and AUGmRNA were the same between 20 and 40°C whereas the GUG and AUUmRNAs were less active and competed poorly with the AUGmRNA, especially at low temperature. Nutrient limitation and preferential inhibition by ppGpp severely affected activity and competitiveness of all mRNAs bearing non-AUG starts, the UUGmRNA being the least affected. Overall, our data indicate that beyond these effects exclusively due to the degenerate start codons within an optimized translational initiation region, an important role is played by the context in which the rare start codons are present.
| S-EPMC5499595 | biostudies-literature
Project description:Mitochondrial mRNAs encode key subunits of the oxidative phosphorylation complexes that produce energy for the cell. In Saccharomyces cerevisiae, mitochondrial translation is under the control of translational activators, specific to each mRNA. In Schizosaccharomyces pombe, which more closely resembles the human system by its mitochondrial DNA structure and physiology, most translational activators appear to be either lacking, or recruited for post-translational functions. By combining bioinformatics, genetic and biochemical approaches we identified two interacting factors, Cbp7 and Cbp8, controlling Cytb production in S. pombe. We show that their absence affects cytb mRNA stability and decreases the accumulation of the Cytb protein. We further identified two classes of Cbp7/Cbp8 partners and showed that they modulated Cytb or Cox1 synthesis. First, two isoforms of bS1m small mitoribosomal subunits, that appear mutually exclusive and confer translational specificity. Second, a complex of four proteins dedicated to Cox1 synthesis, which includes an RNA helicase that interacts with the mitochondrial ribosome. Our results suggest that S. pombecontains, in addition to complexes of translational activators, a heterogeneous population of mitochondrial ribosomes that could specifically modulate translation depending on the mRNA translated, in order to optimally balance the production of different respiratory complex subunits.
2021-10-11 | PXD025400 | Pride