1
|
Using a Hand-Held Gene Gun for Genetic Transformation of Tetrahymena thermophila. Methods Mol Biol 2021. [PMID: 34542863 DOI: 10.1007/978-1-0716-1661-1_18] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Biolistic bombardment is widely used as a means of delivering vector-coated microparticles into microorganisms, cultured cells, and tissues. The first particle delivery system contained a helium propulsion unit (the gun) mounted in a vacuum-controlled chamber. In contrast, the hand-held gene gun does not operate within a chamber. It is completely hand-held, easy, and efficient to use, and it requires minimal space on the laboratory bench top. This chapter describes protocols for using a hand-held gene gun to deliver transformation vectors for overexpression of genes or gene replacement into the macronucleus of Tetrahymena thermophila. The protocols provide helpful information for preparing Tetrahymena for biolistic bombardment, preparation of vector-coated microcarriers, and basic gene gun operating procedures.
Collapse
|
2
|
Nabeel-Shah S, Garg J, Kougnassoukou Tchara PE, Pearlman RE, Lambert JP, Fillingham J. Functional proteomics protocol for the identification of interaction partners in Tetrahymena thermophila. STAR Protoc 2021; 2:100362. [PMID: 33786459 PMCID: PMC7988224 DOI: 10.1016/j.xpro.2021.100362] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
Abstract
We describe an optimized protocol for one-step affinity purification of FZZ-tagged proteins followed by mass spectrometry analysis for the identification of protein-protein interactions in the ciliate protozoan Tetrahymena thermophila. The FZZ epitope tag contains 2 protein A moieties (ZZ) and a 3xFLAG separated by a TEV cleavage site, which can also be employed in tandem affinity purification. This protocol is versatile and is suitable to use for other common epitope tags and can be adapted for other ciliates. For complete details on the use and execution of this protocol, please refer to Garg et al. (2019).
Collapse
Affiliation(s)
- Syed Nabeel-Shah
- Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada
- Donnelly Centre, University of Toronto, Toronto, ON, M5S 3E1, Canada
- Department of Molecular Genetics, University of Toronto, Toronto, ON, M5S 1A8, Canada
| | - Jyoti Garg
- Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada
- Department of Biology, York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada
| | - Pata-Eting Kougnassoukou Tchara
- Department of Molecular Medicine, Cancer Research Center, Big Data Research Center, Université Laval, Quebec City, QC, Canada
- CHU de Québec Research Center, CHUL, 2705 Laurier Boulevard, Quebec City, QC, G1V 4G2, Canada
| | - Ronald E. Pearlman
- Department of Biology, York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada
| | - Jean-Philippe Lambert
- Department of Molecular Medicine, Cancer Research Center, Big Data Research Center, Université Laval, Quebec City, QC, Canada
- CHU de Québec Research Center, CHUL, 2705 Laurier Boulevard, Quebec City, QC, G1V 4G2, Canada
| | - Jeffrey Fillingham
- Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada
| |
Collapse
|
3
|
Han X, Yan G, Ma Y, Miao W, Wang G. Sequencing and characterization of the macronuclear rDNA minichromosome of the protozoan Tetrahymena pyriformis. Int J Biol Macromol 2020; 147:576-581. [PMID: 31931068 DOI: 10.1016/j.ijbiomac.2020.01.063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2019] [Revised: 12/06/2019] [Accepted: 01/06/2020] [Indexed: 10/25/2022]
Abstract
Tetrahymena ribosomal DNA (rDNA) is an ideal system for studying eukaryotic DNA replication and gene transcription. In this study, we developed a new method to isolate rDNA from Tetrahymena cells and used it to sequence and annotate the complete 19,670 bp macronuclear rDNA minichromosome of Tetrahymena pyriformis, a species that lacks the germ-line micronucleus and is unable to undergo sexual reproduction. The key features of T. pyriformis and Tetrahymena thermophila rDNA sequences were then compared. Our results showed (i) the short inverted repeats (M repeats) essential for formation of rDNA minichromosome palindromic structure during sexual reproduction in Tetrahymena are highly conserved in T. pyriformis; (ii) in contrast to T. thermophila, which has two tandem domains that coordinately regulate rDNA replication, T. pyriformis has only a single domain; (iii) the 35S pre-rRNA precursor has 80.25% similarity between the two species; and (iv) the G + C content is higher in the transcribed region than the non-transcribed region in both species, but the GC-skew is more stable in T. pyriformis. The new isolation method and annotated information for the T. pyriformis rDNA minichromosome will provide a useful resource for studying DNA replication and chromosome copy number control in Tetrahymena.
Collapse
Affiliation(s)
- Xiaojie Han
- College of Fisheries and Life Science, Dalian Ocean University, Dalian 116023, China; Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Guanxiong Yan
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yang Ma
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Wei Miao
- College of Fisheries and Life Science, Dalian Ocean University, Dalian 116023, China; Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China; State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; CAS Center for Excellence in Animal Evolution and Genetics, Kunming 650223, China
| | - Guangying Wang
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.
| |
Collapse
|
4
|
Louka P, Vasudevan KK, Guha M, Joachimiak E, Wloga D, Tomasi RFX, Baroud CN, Dupuis-Williams P, Galati DF, Pearson CG, Rice LM, Moresco JJ, Yates JR, Jiang YY, Lechtreck K, Dentler W, Gaertig J. Proteins that control the geometry of microtubules at the ends of cilia. J Cell Biol 2018; 217:4298-4313. [PMID: 30217954 PMCID: PMC6279374 DOI: 10.1083/jcb.201804141] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Revised: 07/25/2018] [Accepted: 08/31/2018] [Indexed: 11/22/2022] Open
Abstract
Louka et al. describe three conserved proteins that regulate the positions of microtubule ends near the tips of cilia. Mutations in two of these proteins cause a brain malformation, Joubert syndrome. Thus, microtubule ends in cilia may play a role in the pathology of Joubert syndrome. Cilia, essential motile and sensory organelles, have several compartments: the basal body, transition zone, and the middle and distal axoneme segments. The distal segment accommodates key functions, including cilium assembly and sensory activities. While the middle segment contains doublet microtubules (incomplete B-tubules fused to complete A-tubules), the distal segment contains only A-tubule extensions, and its existence requires coordination of microtubule length at the nanometer scale. We show that three conserved proteins, two of which are mutated in the ciliopathy Joubert syndrome, determine the geometry of the distal segment, by controlling the positions of specific microtubule ends. FAP256/CEP104 promotes A-tubule elongation. CHE-12/Crescerin and ARMC9 act as positive and negative regulators of B-tubule length, respectively. We show that defects in the distal segment dimensions are associated with motile and sensory deficiencies of cilia. Our observations suggest that abnormalities in distal segment organization cause a subset of Joubert syndrome cases.
Collapse
Affiliation(s)
- Panagiota Louka
- Department of Cellular Biology, University of Georgia, Athens, GA
| | | | - Mayukh Guha
- Department of Cellular Biology, University of Georgia, Athens, GA
| | - Ewa Joachimiak
- Laboratory of Cytoskeleton and Cilia Biology, Nencki Institute of Experimental Biology of Polish Academy of Sciences, Warsaw, Poland
| | - Dorota Wloga
- Laboratory of Cytoskeleton and Cilia Biology, Nencki Institute of Experimental Biology of Polish Academy of Sciences, Warsaw, Poland
| | - Raphaël F-X Tomasi
- Department of Mechanics, LadHyX, Ecole Polytechnique-Centre National de la Recherche Scientifique, Palaiseau, France
| | - Charles N Baroud
- Department of Mechanics, LadHyX, Ecole Polytechnique-Centre National de la Recherche Scientifique, Palaiseau, France
| | - Pascale Dupuis-Williams
- UMR-S1174 Institut National de la Santé et de la Recherche Médicale, Université Paris-Sud, Bat 443, Orsay, France.,École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris, Paris, France
| | - Domenico F Galati
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO
| | - Chad G Pearson
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO
| | - Luke M Rice
- Departments of Biophysics and Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX
| | - James J Moresco
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA
| | - John R Yates
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA
| | - Yu-Yang Jiang
- Department of Cellular Biology, University of Georgia, Athens, GA
| | - Karl Lechtreck
- Department of Cellular Biology, University of Georgia, Athens, GA
| | - William Dentler
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS
| | - Jacek Gaertig
- Department of Cellular Biology, University of Georgia, Athens, GA
| |
Collapse
|
5
|
Tetrahymena as a Unicellular Model Eukaryote: Genetic and Genomic Tools. Genetics 2017; 203:649-65. [PMID: 27270699 DOI: 10.1534/genetics.114.169748] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Accepted: 04/08/2016] [Indexed: 12/12/2022] Open
Abstract
Tetrahymena thermophila is a ciliate model organism whose study has led to important discoveries and insights into both conserved and divergent biological processes. In this review, we describe the tools for the use of Tetrahymena as a model eukaryote, including an overview of its life cycle, orientation to its evolutionary roots, and methodological approaches to forward and reverse genetics. Recent genomic tools have expanded Tetrahymena's utility as a genetic model system. With the unique advantages that Tetrahymena provide, we argue that it will continue to be a model organism of choice.
Collapse
|
6
|
Farley BM, Collins K. Transgenerational function of Tetrahymena Piwi protein Twi8p at distinctive noncoding RNA loci. RNA (NEW YORK, N.Y.) 2017; 23:530-545. [PMID: 28053272 PMCID: PMC5340916 DOI: 10.1261/rna.060012.116] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 12/29/2016] [Indexed: 06/06/2023]
Abstract
Transgenerational transmission of genome-regulatory epigenetic information can determine phenotypes in the progeny of sexual reproduction. Sequence specificity of transgenerational regulation derives from small RNAs assembled into Piwi-protein complexes. Known targets of transgenerational regulation are primarily transposons and transposon-derived sequences. Here, we extend the scope of Piwi-mediated transgenerational regulation to include unique noncoding RNA loci. Ciliates such as Tetrahymena have a phenotypically silent germline micronucleus and an expressed somatic macronucleus, which is differentiated anew from a germline genome copy in sexual reproduction. We show that the nuclear-localized Tetrahymena Piwi protein Twi8p shuttles from parental to zygotic macronuclei. Genetic elimination of Twi8p has no phenotype for cells in asexual growth. On the other hand, cells lacking Twi8p arrest in sexual reproduction with zygotic nuclei that retain the germline genome structure, without the DNA elimination and fragmentation required to generate a functional macronucleus. Twi8p-bound small RNAs originate from long-noncoding RNAs with a terminal hairpin, which become detectable in the absence of Twi8p. Curiously, the loci that generate Twi8p-bound small RNAs are essential for asexual cell growth, even though Twi8 RNPs are essential only in sexual reproduction. Our findings suggest the model that Twi8 RNPs act on silent germline chromosomes to permit their conversion to expressed macronuclear chromosomes. Overall this work reveals that a Piwi protein carrying small RNAs from long-noncoding RNA loci has transgenerational function in establishing zygotic nucleus competence for gene expression.
Collapse
MESH Headings
- Argonaute Proteins/genetics
- Argonaute Proteins/metabolism
- Chromosomes
- DNA, Protozoan/genetics
- DNA, Protozoan/metabolism
- Gene Rearrangement
- Genome, Protozoan
- Macronucleus/genetics
- Macronucleus/metabolism
- Micronucleus, Germline/genetics
- Micronucleus, Germline/metabolism
- Protozoan Proteins/genetics
- Protozoan Proteins/metabolism
- RNA, Protozoan/genetics
- RNA, Protozoan/metabolism
- RNA, Small Interfering/genetics
- RNA, Small Interfering/metabolism
- Reproduction, Asexual/genetics
- Tetrahymena/genetics
- Tetrahymena/growth & development
- Tetrahymena/metabolism
Collapse
Affiliation(s)
- Brian M Farley
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720-3202, USA
| | - Kathleen Collins
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720-3202, USA
| |
Collapse
|
7
|
Upton HE, Chan H, Feigon J, Collins K. Shared Subunits of Tetrahymena Telomerase Holoenzyme and Replication Protein A Have Different Functions in Different Cellular Complexes. J Biol Chem 2016; 292:217-228. [PMID: 27895115 DOI: 10.1074/jbc.m116.763664] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Revised: 11/17/2016] [Indexed: 11/06/2022] Open
Abstract
In most eukaryotes, telomere maintenance relies on telomeric repeat synthesis by a reverse transcriptase named telomerase. To synthesize telomeric repeats, the catalytic subunit telomerase reverse transcriptase (TERT) uses the RNA subunit (TER) as a template. In the ciliate Tetrahymena thermophila, the telomerase holoenzyme consists of TER, TERT, and eight additional proteins, including the telomeric repeat single-stranded DNA-binding protein Teb1 and its heterotrimer partners Teb2 and Teb3. Teb1 is paralogous to the large subunit of the general single-stranded DNA binding heterotrimer replication protein A (RPA). Little is known about the function of Teb2 and Teb3, which are structurally homologous to the RPA middle and small subunits, respectively. Here, epitope-tagging Teb2 and Teb3 expressed at their endogenous gene loci enabled affinity purifications that revealed that, unlike other Tetrahymena telomerase holoenzyme subunits, Teb2 and Teb3 are not telomerase-specific. Teb2 and Teb3 assembled into other heterotrimer complexes, which when recombinantly expressed had the general single-stranded DNA binding activity of RPA complexes, unlike the telomere-specific DNA binding of Teb1 or the TEB heterotrimer of Teb1, Teb2, and Teb3. TEB had no more DNA binding affinity than Teb1 alone. In contrast, heterotrimers reconstituted with Teb2 and Teb3 and two other Tetrahymena RPA large subunit paralogs had higher DNA binding affinity than their large subunit alone. Teb1 and TEB, but not RPA, increased telomerase processivity. We conclude that in the telomerase holoenzyme, instead of binding DNA, Teb2 and Teb3 are Teb1 assembly factors. These findings demonstrate that Tetrahymena telomerase holoenzyme and RPA complexes share subunits and that RPA subunits have distinct functions in different heterotrimer assemblies.
Collapse
Affiliation(s)
- Heather E Upton
- From the Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202 and
| | - Henry Chan
- the Department of Chemistry and Biochemistry, UCLA, Los Angeles, California 90095
| | - Juli Feigon
- the Department of Chemistry and Biochemistry, UCLA, Los Angeles, California 90095
| | - Kathleen Collins
- From the Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202 and
| |
Collapse
|
8
|
Gotesman M, Williams SA. Using a Handheld Gene Gun for Genetic Transformation of Tetrahymena thermophila. Methods Mol Biol 2016; 1365:373-383. [PMID: 26498798 DOI: 10.1007/978-1-4939-3124-8_22] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
This chapter describes protocols for using a handheld gene gun to deliver transformation vectors for overexpression of genes or gene replacement in the macronucleus of Tetrahymena thermophila. The protocols provide helpful information for preparing Tetrahymena for biolistic bombardment, preparation of vector-coated microcarriers, and basic gene gun operating procedures.
Collapse
Affiliation(s)
- Michael Gotesman
- Department of Biology, Technion - Israel Institute of Technology, Technion, Haifa, 3200003, Israel.
| | | |
Collapse
|
9
|
Direct single-stranded DNA binding by Teb1 mediates the recruitment of Tetrahymena thermophila telomerase to telomeres. Mol Cell Biol 2014; 34:4200-12. [PMID: 25225329 DOI: 10.1128/mcb.01030-14] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The eukaryotic reverse transcriptase telomerase copies its internal RNA template to synthesize telomeric DNA repeats at chromosome ends in balance with sequence loss during cell proliferation. Previous work has established several factors involved in telomerase recruitment to telomeres in yeast and mammalian cells; however, it remains unclear what determines the association of telomerase with telomeres in other organisms. Here we investigate the cell cycle dependence of telomere binding by each of the seven Tetrahymena thermophila telomerase holoenzyme proteins TERT, p65, Teb1, p50, p75, p45, and p19. We observed coordinate cell cycle-regulated recruitment and release of all of the subunits, including the telomeric-repeat DNA-binding subunit Teb1. Using domain truncation and mutagenesis approaches, we investigated which subunits govern the interaction of telomerase holoenzyme with telomeres. Our results show that Teb1 is critical for telomere interaction of other holoenzyme subunits and demonstrate that high-affinity Teb1 DNA-binding activity is necessary and sufficient for cell cycle-regulated telomere association. Overall, these and additional findings indicate that in the ciliate Tetrahymena, telomerase recruitment to telomeres requires direct binding to single-stranded DNA, unlike the indirect DNA recognition through telomere-bound proteins essential in yeast and mammalian cells.
Collapse
|
10
|
Hong K, Upton H, Miracco EJ, Jiang J, Zhou ZH, Feigon J, Collins K. Tetrahymena telomerase holoenzyme assembly, activation, and inhibition by domains of the p50 central hub. Mol Cell Biol 2013; 33:3962-71. [PMID: 23918804 PMCID: PMC3811867 DOI: 10.1128/mcb.00792-13] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Accepted: 07/29/2013] [Indexed: 01/10/2023] Open
Abstract
The eukaryotic reverse transcriptase, telomerase, adds tandem telomeric repeats to chromosome ends to promote genome stability. The fully assembled telomerase holoenzyme contains a ribonucleoprotein (RNP) catalytic core and additional proteins that modulate the ability of the RNP catalytic core to elongate telomeres. Electron microscopy (EM) structures of Tetrahymena telomerase holoenzyme revealed a central location of the relatively uncharacterized p50 subunit. Here we have investigated the biochemical and structural basis for p50 function. We have shown that the p50-bound RNP catalytic core has a relatively low rate of tandem repeat synthesis but high processivity of repeat addition, indicative of high stability of enzyme-product interaction. The rate of tandem repeat synthesis is enhanced by p50-dependent recruitment of the holoenzyme single-stranded DNA binding subunit, Teb1. An N-terminal p50 domain is sufficient to stimulate tandem repeat synthesis and bridge the RNP catalytic core, Teb1, and the p75 subunit of the holoenzyme subcomplex p75/p19/p45. In cells, the N-terminal p50 domain assembles a complete holoenzyme that is functional for telomere maintenance, albeit at shortened telomere lengths. Also, in EM structures of holoenzymes, only the N-terminal domain of p50 is visible. Our findings provide new insights about subunit and domain interactions and functions within the Tetrahymena telomerase holoenzyme.
Collapse
Affiliation(s)
- Kyungah Hong
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
| | - Heather Upton
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
| | - Edward J. Miracco
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA
| | - Jiansen Jiang
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, California, USA
| | - Z. Hong Zhou
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, California, USA
| | - Juli Feigon
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA
| | - Kathleen Collins
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
| |
Collapse
|
11
|
Jiang J, Miracco EJ, Hong K, Eckert B, Chan H, Cash DD, Min B, Zhou ZH, Collins K, Feigon J. The architecture of Tetrahymena telomerase holoenzyme. Nature 2013; 496:187-92. [PMID: 23552895 PMCID: PMC3817743 DOI: 10.1038/nature12062] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2012] [Accepted: 03/08/2013] [Indexed: 01/15/2023]
Abstract
Telomerase adds telomeric repeats to chromosome ends using an internal RNA template and a specialized telomerase reverse transcriptase (TERT), thereby maintaining genome integrity. Little is known about the physical relationships among protein and RNA subunits within a biologically functional holoenzyme. Here we describe the architecture of Tetrahymena thermophila telomerase holoenzyme determined by electron microscopy. Six of the seven proteins and the TERT-binding regions of telomerase RNA (TER) have been localized by affinity labelling. Fitting with high-resolution structures reveals the organization of TERT, TER and p65 in the ribonucleoprotein (RNP) catalytic core. p50 has an unanticipated role as a hub between the RNP catalytic core, p75-p19-p45 subcomplex, and the DNA-binding Teb1. A complete in vitro holoenzyme reconstitution assigns function to these interactions in processive telomeric repeat synthesis. These studies provide the first view of the extensive network of subunit associations necessary for telomerase holoenzyme assembly and physiological function.
Collapse
Affiliation(s)
- Jiansen Jiang
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, California 90095, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
12
|
A Tetrahymena Piwi bound to mature tRNA 3' fragments activates the exonuclease Xrn2 for RNA processing in the nucleus. Mol Cell 2012; 48:509-20. [PMID: 23084833 DOI: 10.1016/j.molcel.2012.09.010] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2012] [Revised: 07/26/2012] [Accepted: 09/07/2012] [Indexed: 11/21/2022]
Abstract
Emerging evidence suggests that Argonaute (Ago)/Piwi proteins have diverse functions in the nucleus and cytoplasm, but the molecular mechanisms employed in the nucleus remain poorly defined. The Tetrahymena thermophila Ago/Piwi protein Twi12 is essential for growth and functions in the nucleus. Twi12-bound small RNAs (sRNAs) are 3' tRNA fragments that contain modified bases and thus are attenuated for base pairing to targets. We show that Twi12 assembles an unexpected complex with the nuclear exonuclease Xrn2. Twi12 functions to stabilize and localize Xrn2, as well as to stimulate its exonuclease activity. Twi12 function depends on sRNA binding, which is required for its nuclear import. Depletion of Twi12 or Xrn2 induces a cellular ribosomal RNA processing defect known to result from limiting Xrn2 activity in other organisms. Our findings suggest a role for an Ago/Piwi protein and 3' tRNA fragments in nuclear RNA metabolism.
Collapse
|