Project description:Yeast large ribosomal subunit (LSU) precursors are subject to substantial changes in protein composition during their maturation due to coordinated transient interactions with a large number of ribosome biogenesis factors and due to the assembly of ribosomal proteins. These compositional changes go along with stepwise processing of LSU rRNA precursors and with specific rRNA folding events, as revealed by recent cryo-electron microscopy analyses of late nuclear and cytoplasmic LSU precursors. Here we aimed to analyze changes in the spatial rRNA surrounding of selected ribosomal proteins during yeast LSU maturation. For this we combined a recently developed tethered tertiary structure probing approach with both targeted and high-throughput readout strategies. Several structural features of late LSU precursors were faithfully detected by this procedure. In addition, the obtained data let us suggest that early rRNA precursor processing events are accompanied by a global transition from a flexible to a spatially restricted rRNA conformation. For intermediate LSU precursors, a number of structural hallmarks could be addressed which include the fold of the internal transcribed spacer between 5.8S rRNA and 25S rRNA, the orientation of the central protuberance and the spatial organization of the interface between LSU rRNA domains I and III.
Project description:Mitochondrial gene expression relies on mitoribosomes to translate mitochondrial mRNAs. The biogenesis of mitoribosomes is an intricate process involving multiple assembly factors. Among these factors, GTP-binding proteins (GTPBPs) play crucial roles. In bacterial systems, numerous GTPBPs are required for ribosome subunit maturation, with EngB being a GTPBP involved in the ribosomal large subunit assembly. In this study, we focused on exploring the function of GTPBP8, the human homolog of EngB. We found that ablation of GTPBP8 leads to the inhibition of mitochondrial translation, resulting in significant impairment of oxidative phosphorylation. Structural analysis of mitoribosomes from GTPBP8 knock-out cells showed the accumulation of mitoribosomal large subunit assembly intermediates that are incapable of forming functional monosomes. Furthermore, fPAR-CLIP analysis revealed that GTPBP8 is an RNA-binding protein that interacts specifically with the mitochondrial ribosome large subunit16S rRNA. Our study highlights the crucial role of GTPBP8 as a component of the mitochondrial gene expression machinery involved in mitochondrial large subunit maturation.
Project description:While the protein composition of various yeast 60S ribosomal subunit assembly intermediates has been studied in detail, little is known about ribosomal RNA (rRNA) structural rearrangements that take place during early 60S assembly steps. Using a high-throughput RNA structure probing method, we provide nucleotide resolution insights into rRNA structural rearrangements during nucleolar 60S assembly. Our results suggest that many rRNA-folding steps, such as folding of 5.8S rRNA, occur at a very specific stage of assembly, and propose that downstream nuclear assembly events can only continue once 5.8S folding has been completed. Our maps of nucleotide flexibility enable making predictions about the establishment of protein-rRNA interactions, providing intriguing insights into the temporal order of protein-rRNA as well as long-range inter-domain rRNA interactions. These data argue that many distant domains in the rRNA can assemble simultaneously during early 60S assembly and underscore the enormous complexity of 60S synthesis.Ribosome biogenesis is a dynamic process that involves the ordered assembly of ribosomal proteins and numerous RNA structural rearrangements. Here the authors apply ChemModSeq, a high-throughput RNA structure probing method, to quantitatively measure changes in RNA flexibility during the nucleolar stages of 60S assembly in yeast.
Project description:Kinetoplastids 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 the most extreme case 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.
Project description:Mitochondrial gene expression relies on mitoribosomes to translate mitochondrial mRNAs. The biogenesis of mitoribosomes is an intricate process involving multiple assembly factors. Among these factors, GTP-binding proteins (GTPBPs) play crucial roles. In bacterial systems, numerous GTPBPs are required for ribosome subunit maturation, with EngB being a GTPBP involved in the ribosomal large subunit assembly. In this study, we focused on exploring the function of GTPBP8, the human homolog of EngB. We found that ablation of GTPBP8 leads to the inhibition of mitochondrial translation, resulting in significant impairment of oxidative phosphorylation. In the absence of GTPBP8, numerous mitoribosomal proteins from both subunits become destabilized, indicating GTPBP8's involvement in synchronized subunit assembly. Furthermore, structural analysis of mitoribosomes from GTPBP8 knock-out cells showed the accumulation of mitoribosomal large subunit assembly intermediates that are incapable of forming functional monosomes. Our study highlights the crucial role of GTPBP8 as a component of the mitochondrial gene expression machinery involved in mitoribosome biogenesis.
Project description:Here we utilized large-scale systematic probing and screening of ~2000 sequence and structural variants based on two long, perfect RNA hairpins to explore the structure and sequence context determining editability.
Project description:RNA structural transitions are important in the function and regulation of RNAs. Here, we reveal a layer of transcriptome organization in the form of RNA folding energies. By probing yeast RNA structures at different temperatures, we obtained relative melting temperatures (Tm) for RNA structures in over 4000 transcripts. Specific signatures of RNA Tm demarcated the polarity of mRNA open reading frames, and highlighted numerous candidate regulatory RNA motifs in 3' untranslated regions. RNA Tm distinguished non-coding versus coding RNAs, identified mRNAs with distinct cellular functions. We identified thousands of putative RNA thermometers, and their presence is predictive of the pattern of RNA decay in vivo during heat shock. The exosome complex recognizes unpaired bases during heat shock to degrade these RNAs, coupling intrinsic structural stabilities to gene regulation. Thus, genome-wide structural dynamics of RNA can parse functional elements of the transcriptome and reveal diverse biological insights. RNA structure probing at 5 different temperatures (23M-BM-0C , 30M-BM-0C , 37M-BM-0C , 55M-BM-0C and 75M-BM-0C) using RNase V1 on polyA-selected log phase S288C yeast RNAs was followed by library construction using a modified SOLiD small RNA cloning kit and deep sequencing on the SOLiD platform. We performed 2 biological replicates for each temperature.
Project description:Mitochondrial gene expression relies on mitoribosomes to translate mitochondrial mRNAs. The biogenesis of mitoribosomes is an intricate process involving multiple assembly factors. Among these factors, GTP-binding proteins (GTPBPs) play crucial roles. In bacterial systems, numerous GTPBPs are required for ribosome subunit maturation, with EngB being a GTPBP involved in the ribosomal large subunit assembly. In this study, we focused on exploring the function of GTPBP8, the human homolog of EngB. We found that ablation of GTPBP8 leads to the inhibition of mitochondrial translation, resulting in significant impairment of oxidative phosphorylation. In the absence of GTPBP8, numerous mitoribosomal proteins from both subunits become destabilized, indicating GTPBP8's involvement in synchronized subunit assembly. Furthermore, structural analysis of mitoribosomes from GTPBP8 knock-out cells showed the accumulation of mitoribosomal large subunit assembly intermediates that are incapable of forming functional monosomes. Our study highlights the crucial role of GTPBP8 as a component of the mitochondrial gene expression machinery involved in mitoribosome biogenesis.
Project description:Early eukaryotic ribosome biogenesis involves large multi-protein complexes, which co-transcriptionally associate with pre-ribosomal RNA to form the small subunit processome. The precise mechanisms by which two of the largest multi-protein complexes – UtpA and UtpB – interact with nascent pre-ribosomal RNA have so far been poorly understood. We have combined biochemical and structural biology approaches with ensembles of RNA-protein cross-linking to elucidate the essential function of both complexes. Here we show that UtpA contains a large composite RNA binding site and captures the 5´ end of pre-ribosomal RNA. UtpB forms an extended structure that binds early pre-ribosomal intermediates in close proximity to key architectural sites such as an RNA duplex formed by the 5´ ETS and U3 snoRNA as well as the 3´ boundary of 18S rRNA. Both complexes therefore act as vital RNA chaperones to initiate eukaryotic ribosome assembly.
Project description:The AAA-ATPase Drg1 is a key factor in eukaryotic ribosome biogenesis that initiates cytoplasmic maturation of the large ribosomal subunit. Drg1 releases the shuttling maturation factor Rlp24 from pre-60S particles shortly after nuclear export, a strict requirement for downstream maturation. The molecular mechanism of release remained elusive. Here, we report a series of cryo-EM structures showing a hand-over-hand translocation mechanism of Drg1 and additional XL-MS data on positioning of Drg1 on pre-60S particles.