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Gerhalter M, Kofler L, Zisser G, Merl-Pham J, Hauck SM, Bergler H. The novel pre-rRNA detection workflow "Riboprobing" allows simple identification of undescribed RNA species. RNA (NEW YORK, N.Y.) 2024; 30:807-823. [PMID: 38580456 PMCID: PMC11182013 DOI: 10.1261/rna.079912.123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2023] [Accepted: 03/16/2024] [Indexed: 04/07/2024]
Abstract
Ribosomes translate mRNA into proteins and are essential for every living organism. In eukaryotes, both ribosomal subunits are rapidly assembled in a strict hierarchical order, starting in the nucleolus with the transcription of a common precursor ribosomal RNA (pre-rRNA). This pre-rRNA encodes three of the four mature rRNAs, which are formed by several, consecutive endonucleolytic and exonucleolytic processing steps. Historically, northern blots are used to analyze the variety of different pre-rRNA species, only allowing rough length estimations. Although this limitation can be overcome with primer extension, both approaches often use radioactivity and are time-consuming and costly. Here, we present "Riboprobing," a linker ligation-based workflow followed by reverse transcription and PCR for easy and fast detection and characterization of pre-rRNA species and their 5' as well as 3' ends. Using standard molecular biology laboratory equipment, "Riboprobing" allows reliable discrimination of pre-rRNA species not resolved by northern blot (e.g., 27SA2, 27SA3, and 27SB pre-rRNA). The method can successfully be used for the analysis of total cell extracts as well as purified pre-ribosomes for a straightforward evaluation of the impact of mutant gene versions or inhibitors. In the course of method development, we identified and characterized a hitherto undescribed aberrant pre-rRNA arising from LiCl inhibition. This pre-rRNA fragment spans from processing site A1 to E, forming a small RNP that lacks most early joining assembly factors. This finding expands our knowledge of how the cell deals with severe pre-rRNA processing defects and demonstrates the strict requirement for the 5'ETS (external transcribed spacer) for the assembly process.
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Affiliation(s)
| | - Lisa Kofler
- Institute of Molecular Biosciences, University of Graz, Graz 8010, Austria
| | - Gertrude Zisser
- Institute of Molecular Biosciences, University of Graz, Graz 8010, Austria
| | - Juliane Merl-Pham
- Metabolomics and Proteomics Core, Helmholtz Center Munich, Munich 80939, Germany
| | - Stefanie M Hauck
- Metabolomics and Proteomics Core, Helmholtz Center Munich, Munich 80939, Germany
| | - Helmut Bergler
- Institute of Molecular Biosciences, University of Graz, Graz 8010, Austria
- BioTechMed-Graz, Graz 8010, Austria
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2
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Wang C, Zhou W, Zhang L, Fu L, Shi W, Qing Y, Lu F, Tang J, Gao X, Zhang A, Jia Z, Zhang Y, Zhao X, Zheng B. Diagnostic yield and novel candidate genes for neurodevelopmental disorders by exome sequencing in an unselected cohort with microcephaly. BMC Genomics 2023; 24:422. [PMID: 37501076 PMCID: PMC10373276 DOI: 10.1186/s12864-023-09505-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Accepted: 07/04/2023] [Indexed: 07/29/2023] Open
Abstract
OBJECTIVES Microcephaly is caused by reduced brain volume and most usually associated with a variety of neurodevelopmental disorders (NDDs). To provide an overview of the diagnostic yield of whole exome sequencing (WES) and promote novel candidates in genetically unsolved families, we studied the clinical and genetic landscape of an unselected Chinese cohort of patients with microcephaly. METHODS We performed WES in an unselected cohort of 103 NDDs patients with microcephaly as one of the features. Full evaluation of potential novel candidate genes was applied in genetically undiagnosed families. Functional validations of selected variants were conducted in cultured cells. To augment the discovery of novel candidates, we queried our genomic sequencing data repository for additional likely disease-causing variants in the identified candidate genes. RESULTS In 65 families (63.1%), causative sequence variants (SVs) and clinically relevant copy number variants (CNVs) with a pathogenic or likely pathogenic (P/LP) level were identified. By incorporating coverage analysis to WES, a pathogenic or likely pathogenic CNV was detected in 15 families (16/103, 15.5%). In another eight families (8/103, 7.8%), we identified variants in newly reported gene (CCND2) and potential novel neurodevelopmental disorders /microcephaly candidate genes, which involved in cell cycle and division (PWP2, CCND2), CDC42/RAC signaling related actin cytoskeletal organization (DOCK9, RHOF), neurogenesis (ELAVL3, PPP1R9B, KCNH3) and transcription regulation (IRF2BP1). By looking into our data repository of 5066 families with NDDs, we identified additional two cases with variants in DOCK9 and PPP1R9B, respectively. CONCLUSION Our results expand the morbid genome of monogenic neurodevelopmental disorders and support the adoption of WES as a first-tier test for individuals with microcephaly.
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Affiliation(s)
- Chunli Wang
- Nanjing Key Laboratory of Pediatrics, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Wei Zhou
- Nanjing Key Laboratory of Pediatrics, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Luyan Zhang
- Nanjing Key Laboratory of Pediatrics, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Luhan Fu
- Nanjing Key Laboratory of Pediatrics, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Wei Shi
- Nanjing Key Laboratory of Pediatrics, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Yan Qing
- Department of Neurosurgery, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Fen Lu
- Department of Rehabilitation Medicine, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Jian Tang
- Department of Rehabilitation Medicine, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Xiucheng Gao
- Department of Radiology, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Aihua Zhang
- Nanjing Key Laboratory of Pediatrics, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Zhanjun Jia
- Nanjing Key Laboratory of Pediatrics, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Yue Zhang
- Jiangsu Key Laboratory of Pediatrics, Nanjing Medical University, Nanjing, China.
| | - Xiaoke Zhao
- Department of Rehabilitation Medicine, Children's Hospital of Nanjing Medical University, Nanjing, China.
| | - Bixia Zheng
- Nanjing Key Laboratory of Pediatrics, Children's Hospital of Nanjing Medical University, Nanjing, China.
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Bruno G, Bergolis VL, Piscazzi A, Crispo F, Condelli V, Zoppoli P, Maddalena F, Pietrafesa M, Giordano G, Matassa DS, Esposito F, Landriscina M. TRAP1 regulates the response of colorectal cancer cells to hypoxia and inhibits ribosome biogenesis under conditions of oxygen deprivation. Int J Oncol 2022; 60:79. [PMID: 35543151 PMCID: PMC9097768 DOI: 10.3892/ijo.2022.5369] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Accepted: 04/12/2022] [Indexed: 11/24/2022] Open
Abstract
Metabolic rewiring fuels rapid cancer cell proliferation by promoting adjustments in energetic resources, and increasing glucose uptake and its conversion into lactate, even in the presence of oxygen. Furthermore, solid tumors often contain hypoxic areas and can rapidly adapt to low oxygen conditions by activating hypoxia inducible factor (HIF)‑1α and several downstream pathways, thus sustaining cell survival and metabolic reprogramming. Since TNF receptor‑associated protein 1 (TRAP1) is a HSP90 molecular chaperone upregulated in several human malignancies and is involved in cancer cell adaptation to unfavorable environments and metabolic reprogramming, in the present study, its role was investigated in the adaptive response to hypoxia in human colorectal cancer (CRC) cells and organoids. In the present study, glucose uptake, lactate production and the expression of key metabolic genes were evaluated in TRAP1‑silenced CRC cell models under conditions of hypoxia/normoxia. Whole genome gene expression profiling was performed in TRAP1‑silenced HCT116 cells exposed to hypoxia to establish the role of TRAP1 in adaptive responses to oxygen deprivation. The results revealed that TRAP1 was involved in regulating hypoxia‑induced HIF‑1α stabilization and glycolytic metabolism and that glucose transporter 1 expression, glucose uptake and lactate production were partially impaired in TRAP1‑silenced CRC cells under hypoxic conditions. At the transcriptional level, the gene expression reprogramming of cancer cells driven by HIF‑1α was partially inhibited in TRAP1‑silenced CRC cells and organoids exposed to hypoxia. Moreover, Gene Set Enrichment Analysis of TRAP1‑silenced HCT116 cells exposed to hypoxia demonstrated that TRAP1 was involved in the regulation of ribosome biogenesis and this occurred with the inhibition of the mTOR pathway. Therefore, as demonstrated herein, TRAP1 is a key factor in maintaining HIF‑1α‑induced genetic/metabolic program under hypoxic conditions and may represent a promising target for novel metabolic therapies.
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Affiliation(s)
- Giuseppina Bruno
- Medical Oncology Unit, Department of Medical and Surgical Sciences, University of Foggia, I-71122 Foggia, Italy
| | - Valeria Li Bergolis
- Medical Oncology Unit, Department of Medical and Surgical Sciences, University of Foggia, I-71122 Foggia, Italy
| | - Annamaria Piscazzi
- Medical Oncology Unit, Department of Medical and Surgical Sciences, University of Foggia, I-71122 Foggia, Italy
| | - Fabiana Crispo
- Laboratory of Pre-Clinical and Translational Research, IRCCS, Referral Cancer Center of Basilicata, I-85028 Rionero in Vulture, Potenza, Italy
| | - Valentina Condelli
- Laboratory of Pre-Clinical and Translational Research, IRCCS, Referral Cancer Center of Basilicata, I-85028 Rionero in Vulture, Potenza, Italy
| | - Pietro Zoppoli
- Laboratory of Pre-Clinical and Translational Research, IRCCS, Referral Cancer Center of Basilicata, I-85028 Rionero in Vulture, Potenza, Italy
| | - Francesca Maddalena
- Laboratory of Pre-Clinical and Translational Research, IRCCS, Referral Cancer Center of Basilicata, I-85028 Rionero in Vulture, Potenza, Italy
| | - Michele Pietrafesa
- Laboratory of Pre-Clinical and Translational Research, IRCCS, Referral Cancer Center of Basilicata, I-85028 Rionero in Vulture, Potenza, Italy
| | - Guido Giordano
- Medical Oncology Unit, Department of Medical and Surgical Sciences, University of Foggia, I-71122 Foggia, Italy
| | - Danilo Swann Matassa
- Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, I-80131 Naples, Italy
| | - Franca Esposito
- Department of Molecular Medicine and Medical Biotechnology, University of Naples Federico II, I-80131 Naples, Italy
| | - Matteo Landriscina
- Medical Oncology Unit, Department of Medical and Surgical Sciences, University of Foggia, I-71122 Foggia, Italy
- Laboratory of Pre-Clinical and Translational Research, IRCCS, Referral Cancer Center of Basilicata, I-85028 Rionero in Vulture, Potenza, Italy
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Dielforder T, Braun CM, Hölzgen F, Li S, Thiele M, Huber M, Ohmayer U, Perez-Fernandez J. Structural Probing with MNase Tethered to Ribosome Assembly Factors Resolves Flexible RNA Regions within the Nascent Pre-Ribosomal RNA. Noncoding RNA 2022; 8:ncrna8010001. [PMID: 35076539 PMCID: PMC8788456 DOI: 10.3390/ncrna8010001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 01/02/2022] [Accepted: 01/05/2022] [Indexed: 12/04/2022] Open
Abstract
The synthesis of ribosomes involves the correct folding of the pre-ribosomal RNA within pre-ribosomal particles. The first ribosomal precursor or small subunit processome assembles stepwise on the nascent transcript of the 35S gene. At the earlier stages, the pre-ribosomal particles undergo structural and compositional changes, resulting in heterogeneous populations of particles with highly flexible regions. Structural probing methods are suitable for resolving these structures and providing evidence about the architecture of ribonucleoprotein complexes. Our approach used MNase tethered to the assembly factors Nan1/Utp17, Utp10, Utp12, and Utp13, which among other factors, initiate the formation of the small subunit processome. Our results provide dynamic information about the folding of the pre-ribosomes by elucidating the relative organization of the 5′ETS and ITS1 regions within the 35S and U3 snoRNA around the C-terminal domains of Nan1/Utp17, Utp10, Utp12, and Utp13.
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Braun C, Knüppel R, Perez-Fernandez J, Ferreira-Cerca S. Non-radioactive In Vivo Labeling of RNA with 4-Thiouracil. Methods Mol Biol 2022; 2533:199-213. [PMID: 35796990 PMCID: PMC9761907 DOI: 10.1007/978-1-0716-2501-9_12] [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] [Indexed: 06/15/2023]
Abstract
RNA molecules and their expression dynamics play essential roles in the establishment of complex cellular phenotypes and/or in the rapid cellular adaption to environmental changes. Accordingly, analyzing RNA expression remains an important step to understand the molecular basis controlling the formation of cellular phenotypes, cellular homeostasis or disease progression. Steady-state RNA levels in the cells are controlled by the sum of highly dynamic molecular processes contributing to RNA expression and can be classified in transcription, maturation and degradation. The main goal of analyzing RNA dynamics is to disentangle the individual contribution of these molecular processes to the life cycle of a given RNA under different physiological conditions. In the recent years, the use of nonradioactive nucleotide/nucleoside analogs and improved chemistry, in combination with time-dependent and high-throughput analysis, have greatly expanded our understanding of RNA metabolism across various cell types, organisms, and growth conditions.In this chapter, we describe a step-by-step protocol allowing pulse labeling of RNA with the nonradioactive nucleotide analog, 4-thiouracil , in the eukaryotic model organism Saccharomyces cerevisiae and the model archaeon Haloferax volcanii .
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Affiliation(s)
- Christina Braun
- Biochemistry III-Institute for Biochemistry, Genetics and Microbiology, University of Regensburg, Regensburg, Germany
| | - Robert Knüppel
- Biochemistry III-Institute for Biochemistry, Genetics and Microbiology, University of Regensburg, Regensburg, Germany
| | - Jorge Perez-Fernandez
- Biochemistry III-Institute for Biochemistry, Genetics and Microbiology, University of Regensburg, Regensburg, Germany.
- Department of Experimental Biology, University of Jaen, Jaén, Spain.
| | - Sébastien Ferreira-Cerca
- Biochemistry III-Institute for Biochemistry, Genetics and Microbiology, University of Regensburg, Regensburg, Germany.
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Smith EM, Benbahouche N, Morris K, Wilczynska A, Gillen S, Schmidt T, Meijer H, Jukes-Jones R, Cain K, Jones C, Stoneley M, Waldron J, Bell C, Fonseca B, Blagden S, Willis A, Bushell M. The mTOR regulated RNA-binding protein LARP1 requires PABPC1 for guided mRNA interaction. Nucleic Acids Res 2021; 49:458-478. [PMID: 33332560 PMCID: PMC7797073 DOI: 10.1093/nar/gkaa1189] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Revised: 11/16/2020] [Accepted: 12/11/2020] [Indexed: 12/16/2022] Open
Abstract
The mammalian target of rapamycin (mTOR) is a critical regulator of cell growth, integrating multiple signalling cues and pathways. Key among the downstream activities of mTOR is the control of the protein synthesis machinery. This is achieved, in part, via the co-ordinated regulation of mRNAs that contain a terminal oligopyrimidine tract (TOP) at their 5'ends, although the mechanisms by which this occurs downstream of mTOR signalling are still unclear. We used RNA-binding protein (RBP) capture to identify changes in the protein-RNA interaction landscape following mTOR inhibition. Upon mTOR inhibition, the binding of LARP1 to a number of mRNAs, including TOP-containing mRNAs, increased. Importantly, non-TOP-containing mRNAs bound by LARP1 are in a translationally-repressed state, even under control conditions. The mRNA interactome of the LARP1-associated protein PABPC1 was found to have a high degree of overlap with that of LARP1 and our data show that PABPC1 is required for the association of LARP1 with its specific mRNA targets. Finally, we demonstrate that mRNAs, including those encoding proteins critical for cell growth and survival, are translationally repressed when bound by both LARP1 and PABPC1.
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Affiliation(s)
- Ewan M Smith
- Cancer Research UK Beatson Institute, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1BD, UK
| | - Nour El Houda Benbahouche
- Cancer Research UK Beatson Institute, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1BD, UK
| | - Katherine Morris
- MRC Toxicology Unit, University of Cambridge, Leicester LE1 9HN, UK
| | - Ania Wilczynska
- Cancer Research UK Beatson Institute, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1BD, UK
- Institute of Cancer Sciences, University of Glasgow, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1QH, UK
| | - Sarah Gillen
- Cancer Research UK Beatson Institute, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1BD, UK
| | - Tobias Schmidt
- Cancer Research UK Beatson Institute, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1BD, UK
| | - Hedda A Meijer
- Division of Cell and Developmental Biology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | | | - Kelvin Cain
- MRC Toxicology Unit, University of Cambridge, Leicester LE1 9HN, UK
| | - Carolyn Jones
- MRC Toxicology Unit, University of Cambridge, Leicester LE1 9HN, UK
| | - Mark Stoneley
- MRC Toxicology Unit, University of Cambridge, Leicester LE1 9HN, UK
| | - Joseph A Waldron
- Cancer Research UK Beatson Institute, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1BD, UK
| | - Cameron Bell
- Cancer Research UK Therapeutic Discovery Laboratories, London Bioscience Innovation Centre, 2 Royal College Street, London NW1 0NH, UK
| | | | - Sarah Blagden
- Department of Oncology, University of Oxford, Oxford, OX3 7LE, UK
| | - Anne E Willis
- MRC Toxicology Unit, University of Cambridge, Leicester LE1 9HN, UK
| | - Martin Bushell
- Cancer Research UK Beatson Institute, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1BD, UK
- Institute of Cancer Sciences, University of Glasgow, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1QH, UK
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Braun CM, Hackert P, Schmid CE, Bohnsack MT, Bohnsack KE, Perez-Fernandez J. Pol5 is required for recycling of small subunit biogenesis factors and for formation of the peptide exit tunnel of the large ribosomal subunit. Nucleic Acids Res 2020; 48:405-420. [PMID: 31745560 PMCID: PMC7145529 DOI: 10.1093/nar/gkz1079] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Revised: 10/29/2019] [Accepted: 11/04/2019] [Indexed: 01/24/2023] Open
Abstract
More than 200 assembly factors (AFs) are required for the production of ribosomes in yeast. The stepwise association and dissociation of these AFs with the pre-ribosomal subunits occurs in a hierarchical manner to ensure correct maturation of the pre-rRNAs and assembly of the ribosomal proteins. Although decades of research have provided a wealth of insights into the functions of many AFs, others remain poorly characterized. Pol5 was initially classified with B-type DNA polymerases, however, several lines of evidence indicate the involvement of this protein in ribosome assembly. Here, we show that depletion of Pol5 affects the processing of pre-rRNAs destined for the both the large and small subunits. Furthermore, we identify binding sites for Pol5 in the 5' external transcribed spacer and within domain III of the 25S rRNA sequence. Consistent with this, we reveal that Pol5 is required for recruitment of ribosomal proteins that form the polypeptide exit tunnel in the LSU and that depletion of Pol5 impairs the release of 5' ETS fragments from early pre-40S particles. The dual functions of Pol5 in 60S assembly and recycling of pre-40S AFs suggest that this factor could contribute to ensuring the stoichiometric production of ribosomal subunits.
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Affiliation(s)
- Christina M Braun
- Department of Biochemistry III, University of Regensburg, Universitätstrasse 31, 93053 Regensburg, Germany
| | - Philipp Hackert
- Department of Molecular Biology, University Medical Center Göttingen, Humboldtallee 23, 37073 Göttingen, Germany
| | - Catharina E Schmid
- Department of Biochemistry III, University of Regensburg, Universitätstrasse 31, 93053 Regensburg, Germany
| | - Markus T Bohnsack
- Department of Molecular Biology, University Medical Center Göttingen, Humboldtallee 23, 37073 Göttingen, Germany.,Göttingen Center for Molecular Biosciences, Georg-August University, Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany
| | - Katherine E Bohnsack
- Department of Molecular Biology, University Medical Center Göttingen, Humboldtallee 23, 37073 Göttingen, Germany
| | - Jorge Perez-Fernandez
- Department of Biochemistry III, University of Regensburg, Universitätstrasse 31, 93053 Regensburg, Germany
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Abstract
In the past 25 years, genetic and biochemical analyses of ribosome assembly in yeast have identified most of the factors that participate in this complex pathway and have generated models for the mechanisms driving the assembly. More recently, the publication of numerous cryo-electron microscopy structures of yeast ribosome assembly intermediates has provided near-atomic resolution snapshots of ribosome precursor particles. Satisfyingly, these structural data support the genetic and biochemical models and provide additional mechanistic insight into ribosome assembly. In this Review, we discuss the mechanisms of assembly of the yeast small ribosomal subunit and large ribosomal subunit in the nucleolus, nucleus and cytoplasm. Particular emphasis is placed on concepts such as the mechanisms of RNA compaction, the functions of molecular switches and molecular mimicry, the irreversibility of assembly checkpoints and the roles of structural and functional proofreading of pre-ribosomal particles.
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Assembly and structure of the SSU processome-a nucleolar precursor of the small ribosomal subunit. Curr Opin Struct Biol 2018; 49:85-93. [PMID: 29414516 DOI: 10.1016/j.sbi.2018.01.008] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2017] [Revised: 01/11/2018] [Accepted: 01/12/2018] [Indexed: 12/22/2022]
Abstract
The small subunit processome is the first precursor of the small eukaryotic ribosomal subunit. During its assembly in the nucleolus, many ribosome biogenesis factors, an RNA chaperone, and ribosomal proteins associate with the nascent pre-rRNA. Biochemical studies have elucidated the rRNA-subdomain dependent recruitment of these factors during SSU processome assembly and have been complemented by structural studies of the assembled particle. Ribosome biogenesis factors encapsulate and guide subdomains of pre-ribosomal RNA in distinct compartments. This prevents uncoordinated maturation and enables processing of regions not accessible in the mature subunit. By sequentially reducing conformational freedom, flexible proteins facilitate the incorporation of dynamic subcomplexes into a globular particle. Large rearrangements within the SSU processome are required for compaction into the mature small ribosomal subunit.
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