Project description:In addition to the conserved translation elongation factors eEF1A and eEF2, fungi require a third essential elongation factor, eEF3. While eEF3 has been implicated in tRNA binding and release at the A and E sites, its exact mechanism of action is unclear. Here we show that eEF3 acts at the mRNA–tRNA translocation step by promoting the dissociation of the tRNA from the E site, but independent of aminoacyl-tRNA recruitment to the A site. Depletion of eEF3 in vivo leads to a general slow-down in translation elongation due to accumulation of ribosomes with an occupied A site. Cryo-EM analysis of native eEF3-ribosome complexes shows that eEF3 facilitates late steps of translocation by favoring non-rotated ribosomal states as well as by opening the L1 stalk to release the E-site tRNA. Additionally, our analysis provides structural insights into novel translation elongation states, enabling presentation of a revised yeast translation elongation cycle.
Project description:While the centrality of post-transcriptional modifications to RNA biology has long been acknowledged, the function of the vast majority of modified sites remains to be discovered. Illustrative of this, there is not yet a discrete biological role assigned for one the most highly conserved modifications, 5-methyluridine at position 54 in tRNAs (m5U54). Here, we uncover contributions of m5U54 to both tRNA maturation and protein synthesis. Our mass spectrometry analyses demonstrate that cells lacking the enzyme that installs m5U in the T-loop (TrmA inE. coli, Trm2 inS. cerevisiae) exhibit altered tRNA modifications patterns. Furthermore, m5U54 deficient tRNAs are desensitized to small molecules that prevent translocationin vitro.This finding is consistent with our observations that, relative to wild-type cells,trm2Δ cell growth and transcriptome-wide gene expression are less perturbed by translocation inhibitors. Together our data suggest a model in which m5U54 acts as an important modulator of tRNA maturation and translocation of the ribosome during protein synthesis.
Project description:In the ribosome complex, tRNA is a critical element of mRNA translation. We reported a new technology for profiling ribosome-embedded tRNAs and their modifications. With the method, we generated a comprehensive survey of the quanity and quality of intra-ribosomal tRNAs (Ribo-tRNA-seq). Ribo-tRNA-seq can provide new insights on translation control mechanism in diverse biological contexts.
Project description:In higher eukaryotes, the large numbers of nuclear-encoded tRNA genes partially ensure the robustness of cytoplasmic protein translation. Here we discover that a loss-of-function in n-Tr20, a member of the nuclear-encoded tRNA Arg UCU family that is expressed specifically in the central nervous systems leads to low but detectable levels of ribosome stalling. In the absence of GTPBP2, a novel binding partner of the ribosome recycling protein Pelota, ribosome stalling increases, leading to widespread neurodegeneration. Our results not only define GTPBP2 as a ribosome rescue factor, but also unmask the disease potential of mutations in nuclear-encoded tRNA genes. In this submission we provide ribosome footprinting data from the cerebella of four strains derived from the C57BL/6J strain with combinations of n-Tr20 and GTPBP2 mutations. Examination of ribosome stalling in cerebella from 4 mouse strains derived from the: C57BL/6J (B6J) strain. The nmf205-/- strain has a homozygous mutation in the gene GTPBP2 while the B6J strain has normal GTPBP2. The n-Tr20 J/J strain has a defect in the n-Tr20 tRNA while the n-Tr20 N/N strain has a functional n-Tr20 tRNA. The 4 strains are the 2x2 combinations of these defects and correctly functioning sequences. 2 replicates for each strain. Please note that only BAM files are included in the records since they form the basis of the study's conclusions. The raw data ribosomal RNA have been filtered and then unique reads mapping to mm10 were computed using tophat and igenome annotations.
Project description:Protein translation depends on mRNA-specific initiation, elongation, and termination rates. While the regulation of ribosome elongation is well studied in bacteria and yeast, less is known in higher eukaryotes. Here, we combined ribosome and tRNA profiling to investigate the relations between ribosome elongation rates, (aminoacyl-) tRNA levels and codon usage in mammals. We modeled codon-specific ribosome dwell times and translation fluxes from ribosome profiling, considering pair-interactions between ribosome sites. In mouse liver, the model revealed site and codon specific dwell times, as well as codon pair-interactions clustering by amino acids. While translation fluxes varied significantly across diurnal time and feeding regimen, codon dwell times were highly stable, and conserved in human. Fasting had no effect on codon dwell times in mouse liver. Profiling of total and aminoacylated tRNAs revealed highly heterogeneous levels with specific isoacceptor patterns and a correlation with codon usage. tRNAs for isoleucine, asparagine, aspartate and arginine were lowly loaded and conserved in fasted mice. Finally, codons with low levels of charged tRNAs and high codon usage relative to tRNA abundance exhibited long dwell times. Together, these analyses pave the way towards understanding the complex relation between tRNA loading, codon usage and ribosome dwell times in mammals.
Project description:Protein translation depends on mRNA-specific initiation, elongation, and termination rates. While the regulation of ribosome elongation is well studied in bacteria and yeast, less is known in higher eukaryotes. Here, we combined ribosome and tRNA profiling to investigate the relations between ribosome elongation rates, (aminoacyl-) tRNA levels and codon usage in mammals. We modeled codon-specific ribosome dwell times and translation fluxes from ribosome profiling, considering pair-interactions between ribosome sites. In mouse liver, the model revealed site and codon specific dwell times, as well as codon pair-interactions clustering by amino acids. While translation fluxes varied significantly across diurnal time and feeding regimen, codon dwell times were highly stable, and conserved in human. Fasting had no effect on codon dwell times in mouse liver. Profiling of total and aminoacylated tRNAs revealed highly heterogeneous levels with specific isoacceptor patterns and a correlation with codon usage. tRNAs for isoleucine, asparagine, aspartate and arginine were lowly loaded and conserved in fasted mice. Finally, codons with low levels of charged tRNAs and high codon usage relative to tRNA abundance exhibited long dwell times. Together, these analyses pave the way towards understanding the complex relation between tRNA loading, codon usage and ribosome dwell times in mammals.
Project description:In higher eukaryotes, the large numbers of nuclear-encoded tRNA genes partially ensure the robustness of cytoplasmic protein translation. Here we discover that a loss-of-function in n-Tr20, a member of the nuclear-encoded tRNA Arg UCU family that is expressed specifically in the central nervous systems leads to low but detectable levels of ribosome stalling. In the absence of GTPBP2, a novel binding partner of the ribosome recycling protein Pelota, ribosome stalling increases, leading to widespread neurodegeneration. Our results not only define GTPBP2 as a ribosome rescue factor, but also unmask the disease potential of mutations in nuclear-encoded tRNA genes. In this submission we provide ribosome footprinting data from the cerebella of four strains derived from the C57BL/6J strain with combinations of n-Tr20 and GTPBP2 mutations.
Project description:We report the changes in ribosome protected fragments as measured by ribosome profiling in cells with or without depletion of tRNA-Tyr-GUA
Project description:Translocon clogging at the endoplasmic reticulum (ER) as a result of translation stalling triggers ribosome UFMylation, activating Translocation-Associated Quality Control (TAQC) to degrade clogged substrates. How cells sense ribosome UFMylation to initiate TAQC is unclear. We conduct a genome-wide CRISPR/Cas9 screen to identify an uncharacterized membrane protein named SAYSD1 that facilitates TAQC. SAYSD1 associates with the Sec61 translocon, and also recognizes both ribosome and UFM1 directly, engaging a stalled nascent chain to ensure its transport via the TRAPP complex to lysosomes for degradation. Like UFM1 deficiency, SAYSD1 depletion causes the accumulation of translocation-stalled proteins at the ER and triggers ER stress. Importantly, disrupting UFM1- and SAYSD1-dependent TAQC in Drosophila leads to intracellular accumulation of translocation-stalled collagens, defective collagen deposition, abnormal basement membranes, and reduced stress tolerance. Thus, SAYSD1 acts as a UFM1 sensor that collaborates with ribosome UFMylation at the site of clogged translocon, safeguarding ER homeostasis during animal development.