1
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Dey A, Monroy-Eklund A, Klotz K, Saha A, Davis J, Li B, Laederach A, Chakrabarti K. In vivo architecture of the telomerase RNA catalytic core in Trypanosoma brucei. Nucleic Acids Res 2021; 49:12445-12466. [PMID: 34850114 PMCID: PMC8643685 DOI: 10.1093/nar/gkab1042] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Revised: 10/11/2021] [Accepted: 10/15/2021] [Indexed: 01/07/2023] Open
Abstract
Telomerase is a unique ribonucleoprotein (RNP) reverse transcriptase that utilizes its cognate RNA molecule as a template for telomere DNA repeat synthesis. Telomerase contains the reverse transcriptase protein, TERT and the template RNA, TR, as its core components. The 5'-half of TR forms a highly conserved catalytic core comprising of the template region and adjacent domains necessary for telomere synthesis. However, how telomerase RNA folding takes place in vivo has not been fully understood due to low abundance of the native RNP. Here, using unicellular pathogen Trypanosoma brucei as a model, we reveal important regional folding information of the native telomerase RNA core domains, i.e. TR template, template boundary element, template proximal helix and Helix IV (eCR4-CR5) domain. For this purpose, we uniquely combined in-cell probing with targeted high-throughput RNA sequencing and mutational mapping under three conditions: in vivo (in WT and TERT-/- cells), in an immunopurified catalytically active telomerase RNP complex and ex vivo (deproteinized). We discover that TR forms at least two different conformers with distinct folding topologies in the insect and mammalian developmental stages of T. brucei. Also, TERT does not significantly affect the RNA folding in vivo, suggesting that the telomerase RNA in T. brucei exists in a conformationally preorganized stable structure. Our observed differences in RNA (TR) folding at two distinct developmental stages of T. brucei suggest that important conformational changes are a key component of T. brucei development.
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Affiliation(s)
- Abhishek Dey
- Department of Biological Sciences, University of North Carolina, Charlotte, NC 28223, USA
| | - Anais Monroy-Eklund
- Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Kaitlin Klotz
- Department of Biological Sciences, University of North Carolina, Charlotte, NC 28223, USA
| | - Arpita Saha
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, Cleveland, OH 44115, USA
| | - Justin Davis
- Department of Biological Sciences, University of North Carolina, Charlotte, NC 28223, USA
| | - Bibo Li
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, Cleveland, OH 44115, USA
| | - Alain Laederach
- Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Kausik Chakrabarti
- To whom correspondence should be addressed. Tel: +1 704 687 1882; Fax: +1 704 687 1488;
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2
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Dong X, Ranganathan S, Qu G, Piazza CL, Belfort M. Structural accommodations accompanying splicing of a group II intron RNP. Nucleic Acids Res 2019; 46:8542-8556. [PMID: 29790987 PMCID: PMC6144810 DOI: 10.1093/nar/gky416] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Accepted: 05/03/2018] [Indexed: 01/21/2023] Open
Abstract
Group II introns, the putative progenitors of spliceosomal introns and retrotransposons, are ribozymes that are capable of self-splicing and DNA invasion. In the cell, group II introns form ribonucleoprotein (RNP) complexes with an intron-encoded protein, which is essential to folding, splicing and retromobility of the intron. To understand the structural accommodations underlying splicing, in preparation for retromobility, we probed the endogenously expressed Lactococcus lactis Ll.LtrB group II intron RNP using SHAPE. The results, which are consistent in vivo and in vitro, provide insights into the dynamics of the intron RNP as well as RNA-RNA and RNA-protein interactions. By comparing the excised intron RNP with mutant RNPs in the precursor state, confined SHAPE profile differences were observed, indicative of rearrangements at the active site as well as disengagement at the functional RNA-protein interface in transition between the two states. The exon-binding sequences in the intron RNA, which interact with the 5' exon and the target DNA, show increased flexibility after splicing. In contrast, stability of major tertiary and protein interactions maintains the scaffold of the RNA through the splicing transition, while the active site is realigned in preparation for retromobility.
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Affiliation(s)
- Xiaolong Dong
- Department of Biological Sciences and RNA Institute, University at Albany, Albany, NY 12222, USA
| | - Srivathsan Ranganathan
- Department of Biological Sciences and RNA Institute, University at Albany, Albany, NY 12222, USA
| | - Guosheng Qu
- Department of Biological Sciences and RNA Institute, University at Albany, Albany, NY 12222, USA
| | - Carol Lyn Piazza
- Department of Biological Sciences and RNA Institute, University at Albany, Albany, NY 12222, USA
| | - Marlene Belfort
- Department of Biological Sciences and RNA Institute, University at Albany, Albany, NY 12222, USA
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3
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Smathers CM, Robart AR. The mechanism of splicing as told by group II introns: Ancestors of the spliceosome. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2019; 1862:194390. [PMID: 31202783 DOI: 10.1016/j.bbagrm.2019.06.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 06/10/2019] [Indexed: 12/31/2022]
Abstract
Spliceosomal introns and self-splicing group II introns share a common mechanism of intron splicing where two sequential transesterification reactions remove intron lariats and ligate exons. The recent revolution in cryo-electron microscopy (cryo-EM) has allowed visualization of the spliceosome's ribozyme core. Comparison of these cryo-EM structures to recent group II intron crystal structures presents an opportunity to draw parallels between the RNA active site, substrate positioning, and product formation in these two model systems of intron splicing. In addition to shared RNA architectural features, structural similarity between group II intron encoded proteins (IEPs) and the integral spliceosomal protein Prp8 further support a shared catalytic core. These mechanistic and structural similarities support the long-held assertion that group II introns and the eukaryotic spliceosome have a common evolutionary origin. In this review, we discuss how recent structural insights into group II introns and the spliceosome facilitate the chemistry of splicing, highlight similarities between the two systems, and discuss their likely evolutionary connections. This article is part of a Special Issue entitled: RNA structure and splicing regulation edited by Francisco Baralle, Ravindra Singh and Stefan Stamm.
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Affiliation(s)
- Claire M Smathers
- Department of Biochemistry, West Virginia University, Morgantown, WV, United States of America
| | - Aaron R Robart
- Department of Biochemistry, West Virginia University, Morgantown, WV, United States of America.
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4
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Wang Y, Feigon J. Structural biology of telomerase and its interaction at telomeres. Curr Opin Struct Biol 2017; 47:77-87. [PMID: 28732250 PMCID: PMC5564310 DOI: 10.1016/j.sbi.2017.06.010] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Accepted: 06/29/2017] [Indexed: 12/21/2022]
Abstract
Telomerase is an RNP that synthesizes the 3' ends of linear chromosomes and is an important regulator of telomere length. It contains a single long non-coding telomerase RNA (TER), telomerase reverse transcriptase (TERT), and other proteins that vary among organisms. Recent progress in structural biology of telomerase includes reports of the first cryo-electron microscopy structure of telomerase, from Tetrahymena, new crystal structures of TERT domains, telomerase RNA structures and models, and identification in Tetrahymena telomerase holoenzyme of human homologues of telomere-associated proteins that have provided a more unified view of telomerase interaction at telomeres as well as insights into the role of telomerase RNA in activity and assembly.
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Affiliation(s)
- Yaqiang Wang
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, CA 90095-1569, USA
| | - Juli Feigon
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, CA 90095-1569, USA.
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5
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Abstract
Telomerase is an RNA-protein complex that extends the 3' ends of linear chromosomes, using a unique telomerase reverse transcriptase (TERT) and template in the telomerase RNA (TR), thereby helping to maintain genome integrity. TR assembles with TERT and species-specific proteins, and telomerase function in vivo requires interaction with telomere-associated proteins. Over the past two decades, structures of domains of TR and TERT as well as other telomerase- and telomere-interacting proteins have provided insights into telomerase function. A recently reported 9-Å cryo-electron microscopy map of the Tetrahymena telomerase holoenzyme has provided a framework for understanding how TR, TERT, and other proteins from ciliate as well as vertebrate telomerase fit and function together as well as unexpected insight into telomerase interaction at telomeres. Here we review progress in understanding the structural basis of human and Tetrahymena telomerase activity, assembly, and interactions.
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Affiliation(s)
- Henry Chan
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569; , ,
| | - Yaqiang Wang
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569; , ,
| | - Juli Feigon
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569; , ,
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6
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Ozturk MB, Li Y, Tergaonkar V. Current Insights to Regulation and Role of Telomerase in Human Diseases. Antioxidants (Basel) 2017; 6:antiox6010017. [PMID: 28264499 PMCID: PMC5384180 DOI: 10.3390/antiox6010017] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 02/16/2017] [Accepted: 02/21/2017] [Indexed: 12/31/2022] Open
Abstract
The telomerase ribonucleoprotein complex has a pivotal role in regulating the proliferation and senescence of normal somatic cells as well as cancer cells. This complex is comprised mainly of telomerase reverse transcriptase (TERT), telomerase RNA component (TERC) and other associated proteins that function to elongate telomeres localized at the end of the chromosomes. While reactivation of telomerase is a major hallmark of most cancers, together with the synergistic activation of other oncogenic signals, deficiency in telomerase and telomeric proteins might lead to aging and senescence-associated disorders. Therefore, it is critically important to understand the canonical as well as non-canonical functions of telomerase through TERT to develop a therapeutic strategy against telomerase-related diseases. In this review, we shed light on the regulation and function of telomerase, and current therapeutic strategies against telomerase in cancer and age-related diseases.
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Affiliation(s)
- Mert Burak Ozturk
- Division of Cancer Genetics and Therapeutics, Laboratory of NFκB Signaling, Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), Singapore 138673, Singapore.
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), Singapore 117597, Singapore.
| | - Yinghui Li
- Division of Cancer Genetics and Therapeutics, Laboratory of NFκB Signaling, Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), Singapore 138673, Singapore.
| | - Vinay Tergaonkar
- Division of Cancer Genetics and Therapeutics, Laboratory of NFκB Signaling, Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), Singapore 138673, Singapore.
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), Singapore 117597, Singapore.
- Centre for Cancer Biology, University of South Australia and SA Pathology, Adelaide SA 5000, Australia.
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7
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Qu G, Kaushal PS, Wang J, Shigematsu H, Piazza CL, Agrawal RK, Belfort M, Wang HW. Structure of a group II intron in complex with its reverse transcriptase. Nat Struct Mol Biol 2016; 23:549-57. [PMID: 27136327 PMCID: PMC4899178 DOI: 10.1038/nsmb.3220] [Citation(s) in RCA: 77] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Accepted: 04/04/2016] [Indexed: 01/08/2023]
Abstract
Bacterial group II introns are large catalytic RNAs related to nuclear spliceosomal introns and eukaryotic retrotransposons. They self-splice, yielding mature RNA, and integrate into DNA as retroelements. A fully active group II intron forms a ribonucleoprotein complex comprising the intron ribozyme and an intron-encoded protein that performs multiple activities including reverse transcription, in which intron RNA is copied into the DNA target. Here we report cryo-EM structures of an endogenously spliced Lactococcus lactis group IIA intron in its ribonucleoprotein complex form at 3.8-Å resolution and in its protein-depleted form at 4.5-Å resolution, revealing functional coordination of the intron RNA with the protein. Remarkably, the protein structure reveals a close relationship between the reverse transcriptase catalytic domain and telomerase, whereas the active splicing center resembles the spliceosomal Prp8 protein. These extraordinary similarities hint at intricate ancestral relationships and provide new insights into splicing and retromobility.
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Affiliation(s)
- Guosheng Qu
- Department of Biological Sciences and RNA Institute, University at Albany, Albany, New York, USA
| | - Prem Singh Kaushal
- Laboratory of Cellular and Molecular Basis of Diseases, Wadsworth Center, New York State Department of Health, Albany, New York, USA
| | - Jia Wang
- Ministry of Education Key Laboratory of Protein Sciences, Tsinghua-Peking Joint Center for Life Sciences, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing, China
| | - Hideki Shigematsu
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut, USA
| | - Carol Lyn Piazza
- Department of Biological Sciences and RNA Institute, University at Albany, Albany, New York, USA
| | - Rajendra Kumar Agrawal
- Laboratory of Cellular and Molecular Basis of Diseases, Wadsworth Center, New York State Department of Health, Albany, New York, USA
- Department of Biomedical Sciences, School of Public Health, University at Albany, Albany, New York, USA
| | - Marlene Belfort
- Department of Biological Sciences and RNA Institute, University at Albany, Albany, New York, USA
- Department of Biomedical Sciences, School of Public Health, University at Albany, Albany, New York, USA
| | - Hong-Wei Wang
- Ministry of Education Key Laboratory of Protein Sciences, Tsinghua-Peking Joint Center for Life Sciences, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing, China
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut, USA
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8
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Matsuguchi T, Blackburn E. The yeast telomerase RNA, TLC1, participates in two distinct modes of TLC1-TLC1 association processes in vivo. PeerJ 2016; 4:e1534. [PMID: 27004145 PMCID: PMC4800423 DOI: 10.7717/peerj.1534] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2015] [Accepted: 12/04/2015] [Indexed: 11/23/2022] Open
Abstract
Telomerase core enzyme minimally consists of the telomerase reverse transcriptase domain-containing protein (Est2 in budding yeast S. cerevisiae) and telomerase RNA, which contains the template specifying the telomeric repeat sequence synthesized. Here we report that in vivo, a fraction of S. cerevisiae telomerase RNA (TLC1) molecules form complexes containing at least two molecules of TLC1, via two separable modes: one requiring a sequence in the 3′ region of the immature TLC1 precursor and the other requiring Ku and Sir4. Such physical TLC1-TLC1 association peaked in G1 phase and did not require telomere silencing, telomere tethering to the nuclear periphery, telomerase holoenzyme assembly, or detectable Est2-Est2 protein association. These data indicate that TLC1-TLC1 associations reflect processes occurring during telomerase biogenesis; we propose that TLC1-TLC1 associations and subsequent reorganization may be regulatory steps in telomerase enzymatic activation.
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Affiliation(s)
- Tet Matsuguchi
- Department of Biochemistry and Biophysics, University of California , San Francisco, CA , United States
| | - Elizabeth Blackburn
- Department of Biochemistry and Biophysics, University of California , San Francisco, CA , United States
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9
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Wu RA, Dagdas YS, Yilmaz ST, Yildiz A, Collins K. Single-molecule imaging of telomerase reverse transcriptase in human telomerase holoenzyme and minimal RNP complexes. eLife 2015; 4. [PMID: 26457608 PMCID: PMC4600948 DOI: 10.7554/elife.08363] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2015] [Accepted: 09/03/2015] [Indexed: 02/07/2023] Open
Abstract
Telomerase synthesizes chromosome-capping telomeric repeats using an active site in telomerase reverse transcriptase (TERT) and an integral RNA subunit template. The fundamental question of whether human telomerase catalytic activity requires cooperation across two TERT subunits remains under debate. In this study, we describe new approaches of subunit labeling for single-molecule imaging, applied to determine the TERT content of complexes assembled in cells or cell extract. Surprisingly, telomerase reconstitutions yielded heterogeneous DNA-bound TERT monomer and dimer complexes in relative amounts that varied with assembly and purification method. Among the complexes, cellular holoenzyme and minimal recombinant enzyme monomeric for TERT had catalytic activity. Dimerization was suppressed by removing a TERT domain linker with atypical sequence bias, which did not inhibit cellular or minimal enzyme assembly or activity. Overall, this work defines human telomerase DNA binding and synthesis properties at single-molecule level and establishes conserved telomerase subunit architecture from single-celled organisms to humans.
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Affiliation(s)
- Robert Alexander Wu
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Yavuz S Dagdas
- Biophysics Graduate Group, University of California, Berkeley, Berkeley, United States
| | - S Tunc Yilmaz
- Department of Physics, University of California, Berkeley, Berkeley, United States
| | - Ahmet Yildiz
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,Department of Physics, University of California, Berkeley, Berkeley, United States
| | - Kathleen Collins
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
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10
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Abstract
In this review, Schmidt and Cech cover human telomerase biogenesis, trafficking, and activation, comparing key aspects with the analogous events in other species. Telomerase is the ribonucleoprotein enzyme that catalyzes the extension of telomeric DNA in eukaryotes. Recent work has begun to reveal key aspects of the assembly of the human telomerase complex, its intracellular trafficking involving Cajal bodies, and its recruitment to telomeres. Once telomerase has been recruited to the telomere, it appears to undergo a separate activation step, which may include an increase in its repeat addition processivity. This review covers human telomerase biogenesis, trafficking, and activation, comparing key aspects with the analogous events in other species.
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Affiliation(s)
- Jens C Schmidt
- Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, BioFrontiers Institute, University of Colorado Boulder, Boulder, Colorado 80309, USA
| | - Thomas R Cech
- Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, BioFrontiers Institute, University of Colorado Boulder, Boulder, Colorado 80309, USA
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11
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Bajon E, Laterreur N, Wellinger RJ. A Single Templating RNA in Yeast Telomerase. Cell Rep 2015; 12:441-8. [PMID: 26166570 DOI: 10.1016/j.celrep.2015.06.045] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Revised: 06/04/2015] [Accepted: 06/13/2015] [Indexed: 12/31/2022] Open
Abstract
The number of essential telomerase components in the active ribonucleoprotein (RNP) has important implications for its mechanism of action yet is by and large unknown. We report that two differentially tagged TLC1 RNAs endogenously expressed in a heterozygous diploid and simultaneously detected via multi-color fluorescence in situ hybridization (FISH) experiments do not co-localize. Probabilistic calculations combined with direct quantification of FISH signals demonstrate that the TLC1 RNA indeed occurs as a single molecule in these RNPs. In addition, two differentially tagged reverse-transcriptase subunits could not be co-immunoprecipitated. These results therefore show that, in yeast cells, telomerase is assembled and matured and occurs as a monomer when not on telomeres. Finally, combining these findings with previous evidence leads us to propose that the enzyme also acts as a monomer when elongating telomeres.
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Affiliation(s)
- Emmanuel Bajon
- Department of Microbiology and Infectious Diseases, Faculty of Medicine, Université de Sherbrooke, 3201, rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada
| | - Nancy Laterreur
- Department of Microbiology and Infectious Diseases, Faculty of Medicine, Université de Sherbrooke, 3201, rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada
| | - Raymund J Wellinger
- Department of Microbiology and Infectious Diseases, Faculty of Medicine, Université de Sherbrooke, 3201, rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada.
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12
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Akiyama BM, Parks JW, Stone MD. The telomerase essential N-terminal domain promotes DNA synthesis by stabilizing short RNA-DNA hybrids. Nucleic Acids Res 2015; 43:5537-49. [PMID: 25940626 PMCID: PMC4477650 DOI: 10.1093/nar/gkv406] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2014] [Accepted: 04/15/2015] [Indexed: 01/11/2023] Open
Abstract
Telomerase is an enzyme that adds repetitive DNA sequences to the ends of chromosomes and consists of two main subunits: the telomerase reverse transcriptase (TERT) protein and an associated telomerase RNA (TER). The telomerase essential N-terminal (TEN) domain is a conserved region of TERT proposed to mediate DNA substrate interactions. Here, we have employed single molecule telomerase binding assays to investigate the function of the TEN domain. Our results reveal telomeric DNA substrates bound to telomerase exhibit a dynamic equilibrium between two states: a docked conformation and an alternative conformation. The relative stabilities of the docked and alternative states correlate with the number of basepairs that can be formed between the DNA substrate and the RNA template, with more basepairing favoring the docked state. The docked state is further buttressed by the TEN domain and mutations within the TEN domain substantially alter the DNA substrate structural equilibrium. We propose a model in which the TEN domain stabilizes short RNA–DNA duplexes in the active site of the enzyme, promoting the docked state to augment telomerase processivity.
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Affiliation(s)
- Benjamin M Akiyama
- Department of Molecular, Cell, and Developmental Biology, University of California, Santa Cruz, CA 95064, USA Center for Molecular Biology of RNA, University of California, Santa Cruz, CA 95064, USA
| | - Joseph W Parks
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA Center for Molecular Biology of RNA, University of California, Santa Cruz, CA 95064, USA
| | - Michael D Stone
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA Center for Molecular Biology of RNA, University of California, Santa Cruz, CA 95064, USA
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13
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Sandin S, Rhodes D. Telomerase structure. Curr Opin Struct Biol 2014; 25:104-10. [PMID: 24704747 PMCID: PMC4045397 DOI: 10.1016/j.sbi.2014.02.003] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 02/17/2014] [Accepted: 02/21/2014] [Indexed: 12/18/2022]
Abstract
First of telomerase architecture. Human telomerase functions as a dimer. Conserved RNA/reverse transcriptase core.
The telomerase reverse transcriptase has an essential role in telomere maintenance and in cancer biology. Progress during the last year has revealed the three-dimensional architecture of both human and ciliate telomerase at about 25 Å resolution, obtained using single particle electron microscopy (EM). The structural analysis of the two holoenzyme complexes isolated from cells shows that whilst the ciliate telomerase is monomeric, the human telomerase is dimeric and only functional as a dimer. We critically discuss the approaches taken to assign the location of protein and RNA subunits, as well as fitting the crystal structure of the catalytic protein subunit in the medium resolution EM density maps. Comparison of the two structural interpretations reveals not only a common RNA/reverse transcriptase core, but also significant differences due to different RNA subunit size and protein composition. These differences suggest that the oligomeric state and subunit composition of telomerase in evolutionary distant organism have evolved.
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Affiliation(s)
- Sara Sandin
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Singapore
| | - Daniela Rhodes
- School of Biological Sciences and LKC Medicine, Proteos, 61 Biopolis Drive, Singapore 138673, Singapore.
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14
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Progress in structural studies of telomerase. Curr Opin Struct Biol 2014; 24:115-24. [PMID: 24508601 DOI: 10.1016/j.sbi.2014.01.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2013] [Revised: 01/01/2014] [Accepted: 01/08/2014] [Indexed: 02/01/2023]
Abstract
Telomerase is the ribonucleoprotein (RNP) reverse transcriptase responsible for synthesizing the 3' ends of linear chromosomes. It plays critical roles in tumorigenesis, cellular aging, and stem cell renewal. The past two years have seen exciting progress in determining telomerase holoenzyme architecture and the structural basis of telomerase activity. Notably, the first electron microscopy structures of telomerase were reported, of the Tetrahymena thermophila telomerase holoenzyme and a human telomerase dimer. In addition to new structures of TERT and TER domains, the first structures of telomerase protein domains beyond TERT, and their complexes with TER or telomeric single-stranded DNA, were reported. Together these studies provide the first glimpse into the organization of the proteins and RNA in the telomerase RNP.
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15
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Cohn EPMT, Wu KL, Pettus TRR, Reich NO. A New Strategy for Detection and Development of Tractable Telomerase Inhibitors. J Med Chem 2012; 55:3678-86. [DOI: 10.1021/jm201191d] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Elysia P. M. T. Cohn
- Department of Chemistry
and Biochemistry, University of California, Santa Barbara, California
93106, United States
| | - Kun-Liang Wu
- Department of Chemistry
and Biochemistry, University of California, Santa Barbara, California
93106, United States
| | - Thomas R. R. Pettus
- Department of Chemistry
and Biochemistry, University of California, Santa Barbara, California
93106, United States
| | - Norbert O. Reich
- Department of Chemistry
and Biochemistry, University of California, Santa Barbara, California
93106, United States
- Program
in Biomolecular Science and Engineering, University of California,
Santa Barbara, California 93106, United States
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16
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17
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Functional importance of telomerase pseudoknot revealed by single-molecule analysis. Proc Natl Acad Sci U S A 2011; 108:20339-44. [PMID: 21571642 DOI: 10.1073/pnas.1017686108] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Telomerase ribonucleoprotein (RNP) employs an RNA subunit to template the addition of telomeric repeats onto chromosome ends. Previous studies have suggested that a region of the RNA downstream of the template may be important for telomerase activity and that the region could fold into a pseudoknot. Whether the pseudoknot motif is formed in the active telomerase RNP and what its functional role is have not yet been conclusively established. Using single-molecule FRET, we show that the isolated pseudoknot sequence stably folds into a pseudoknot. However, in the context of the full-length telomerase RNA, interference by other parts of the RNA prevents the formation of the pseudoknot. The protein subunits of the telomerase holoenzyme counteract RNA-induced misfolding and allow a significant fraction of the RNPs to form the pseudoknot structure. Only those RNP complexes containing a properly folded pseudoknot are catalytically active. These results not only demonstrate the functional importance of the pseudoknot but also reveal the critical role played by telomerase proteins in pseudoknot folding.
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18
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Abstract
Ribonucleoproteins (RNPs) play key roles in many cellular processes and often function as RNP enzymes. Similar to proteins, some of these RNPs exist and function as multimers, either homomeric or heteromeric. While in some cases the mechanistic function of multimerization is well understood, the functional consequences of multimerization of other RNPs remain enigmatic. In this review we will discuss the function and organization of small RNPs that exist as stable multimers, including RNPs catalyzing RNA chemical modifications, telomerase RNP, and RNPs involved in pre-mRNA splicing.
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19
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Wu JY, Stone MD, Zhuang X. A single-molecule assay for telomerase structure-function analysis. Nucleic Acids Res 2009; 38:e16. [PMID: 19920121 PMCID: PMC2817460 DOI: 10.1093/nar/gkp1033] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The activity of the telomerase ribonucleoprotein enzyme is essential for the maintenance of genome stability and normal cell development. Despite the biomedical importance of telomerase activity, detailed structural models for the enzyme remain to be established. Here we report a single-molecule assay for direct structural analysis of catalytically active telomerase enzymes. In this assay, oligonucleotide hybridization was used to probe the primer-extension activity of individual telomerase enzymes with single nucleotide sensitivity, allowing precise discrimination between inactive, active and processive enzyme binding events. FRET signals from enzyme molecules during the active and processive binding events were then used to determine the global organization of telomerase RNA within catalytically active holoenzymes. Using this assay, we have identified an active conformation of telomerase among a heterogeneous population of enzymes with distinct structures.
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Affiliation(s)
- John Y Wu
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA
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20
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Shcherbakova DM, Sokolov KA, Zvereva MI, Dontsova OA. Telomerase from yeast Saccharomyces cerevisiae is active in vitro as a monomer. BIOCHEMISTRY (MOSCOW) 2009; 74:749-55. [PMID: 19747095 DOI: 10.1134/s0006297909070074] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
A system for isolation of yeast telomerase via RNA affinity tag in TLC1 RNA was developed. Streptavidin aptamer was inserted at two different positions in TLC1 RNA. Telomerase with TLC1 RNA with one of these inserts is functional in vivo and can be isolated by affinity chromatography in vitro. A telomerase preparation isolated using this technique from a strain producing two distinguishable TLC1 RNA molecules (with and without aptameric insertion) resulted in isolation of active telomerase containing only TLC1 RNA with the aptamer. Our results indicate that yeast telomerase is active in vitro as a monomer.
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Affiliation(s)
- D M Shcherbakova
- Faculty of Chemistry, Lomonosov Moscow State University, Moscow, 119992, Russia
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21
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Sekaran VG, Soares J, Jarstfer MB. Structures of telomerase subunits provide functional insights. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2009; 1804:1190-201. [PMID: 19665593 DOI: 10.1016/j.bbapap.2009.07.019] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2009] [Revised: 07/09/2009] [Accepted: 07/28/2009] [Indexed: 01/14/2023]
Abstract
BACKGROUND Telomerase continues to generate substantial attention both because of its pivotal roles in cellular proliferation and aging and because of its unusual structure and mechanism. By replenishing telomeric DNA lost during the cell cycle, telomerase overcomes one of the many hurdles facing cellular immortalization. Functionally, telomerase is a reverse transcriptase, and it shares structural and mechanistic features with this class of nucleotide polymerases. Telomerase is a very unusual reverse transcriptase because it remains stably associated with its template and because it reverse transcribes multiple copies of its template onto a single primer in one reaction cycle. SCOPE OF REVIEW Here, we review recent findings that illuminate our understanding of telomerase. Even though the specific emphasis is on structure and mechanism, we also highlight new insights into the roles of telomerase in human biology. GENERAL SIGNIFICANCE Recent advances in the structural biology of telomerase, including high resolution structures of the catalytic subunit of a beetle telomerase and two domains of a ciliate telomerase catalytic subunit, provide new perspectives into telomerase biochemistry and reveal new puzzles.
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Affiliation(s)
- Vijay G Sekaran
- Division of Medicinal Chemistry and Natural Products, Eshelman School of Pharmacy, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
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22
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23
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Structure of the Tribolium castaneum telomerase catalytic subunit TERT. Nature 2008; 455:633-7. [PMID: 18758444 DOI: 10.1038/nature07283] [Citation(s) in RCA: 203] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Accepted: 07/23/2008] [Indexed: 01/26/2023]
Abstract
A common hallmark of human cancers is the overexpression of telomerase, a ribonucleoprotein complex that is responsible for maintaining the length and integrity of chromosome ends. Telomere length deregulation and telomerase activation is an early, and perhaps necessary, step in cancer cell evolution. Here we present the high-resolution structure of the Tribolium castaneum catalytic subunit of telomerase, TERT. The protein consists of three highly conserved domains, organized into a ring-like structure that shares common features with retroviral reverse transcriptases, viral RNA polymerases and B-family DNA polymerases. Domain organization places motifs implicated in substrate binding and catalysis in the interior of the ring, which can accommodate seven to eight bases of double-stranded nucleic acid. Modelling of an RNA-DNA heteroduplex in the interior of this ring demonstrates a perfect fit between the protein and the nucleic acid substrate, and positions the 3'-end of the DNA primer at the active site of the enzyme, providing evidence for the formation of an active telomerase elongation complex.
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24
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Disease-associated human telomerase RNA variants show loss of function for telomere synthesis without dominant-negative interference. Mol Cell Biol 2008; 28:6510-20. [PMID: 18710936 DOI: 10.1128/mcb.00777-08] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Telomerase adds simple-sequence repeats to chromosome ends to offset the terminal sequence loss inherent in each cycle of genome replication. Inherited mutations in genes encoding subunits of the human telomerase holoenzyme give rise to disease phenotypes including hematopoietic failure and pulmonary fibrosis. Disease-associated variants of the human telomerase RNA are expressed in heterozygous combination with wild-type telomerase RNA. Here, we exploit a sensitized human primary cell assay system to investigate the biological function of disease-linked telomerase RNA variants and their impact on the function of coexpressed wild-type telomerase RNA. We find that telomerase RNA variants discovered in patients with dyskeratosis congenita or aplastic anemia show loss of function without any indication of dominant-negative impact on telomere maintenance by the coexpressed wild-type RNA. To reconcile this result with contradictory findings from reconstitution assays in vitro, we demonstrate that the lack of dominant-negative impact on telomere maintenance correlates with physiological assembly of active human telomerase holoenzyme ribonucleoproteins harboring monomers rather than higher-order multimers of telomerase RNA and telomerase reverse transcriptase. These findings support loss of function of telomerase RNA as a general mechanism of human disease.
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25
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Alves D, Li H, Codrington R, Orte A, Ren X, Klenerman D, Balasubramanian S. Single-molecule analysis of human telomerase monomer. Nat Chem Biol 2008; 4:287-9. [DOI: 10.1038/nchembio.82] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2007] [Accepted: 02/29/2008] [Indexed: 11/09/2022]
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26
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Finger SN, Bryan TM. Multiple DNA-binding sites in Tetrahymena telomerase. Nucleic Acids Res 2008; 36:1260-72. [PMID: 18174223 PMCID: PMC2275084 DOI: 10.1093/nar/gkm866] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2007] [Revised: 09/13/2007] [Accepted: 09/24/2007] [Indexed: 12/20/2022] Open
Abstract
Telomerase is a ribonucleoprotein enzyme that maintains chromosome ends through de novo addition of telomeric DNA. The ability of telomerase to interact with its DNA substrate at sites outside its catalytic centre ('anchor sites') is important for its unique ability to undergo repeat addition processivity. We have developed a direct and quantitative equilibrium primer-binding assay to measure DNA-binding affinities of regions of the catalytic protein subunit of recombinant Tetrahymena telomerase (TERT). There are specific telomeric DNA-binding sites in at least four regions of TERT (the TEN, RBD, RT and C-terminal domains). Together, these sites contribute to specific and high-affinity DNA binding, with a K(d) of approximately 8 nM. Both the K(m) and K(d) increased in a stepwise manner as the primer length was reduced; thus recombinant Tetrahymena telomerase, like the endogenous enzyme, contains multiple anchor sites. The N-terminal TEN domain, which has previously been implicated in DNA binding, shows only low affinity binding. However, there appears to be cooperativity between the TEN and RNA-binding domains. Our data suggest that different DNA-binding sites are used by the enzyme during different stages of the addition cycle.
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Affiliation(s)
| | - Tracy M. Bryan
- Children's Medical Research Institute, 214 Hawkesbury Road, Westmead NSW 2145 and University of Sydney, NSW 2006, Australia
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27
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Bryan TM, Jarstfer MB. Interrogation of G-quadruplex–protein interactions. Methods 2007; 43:332-9. [DOI: 10.1016/j.ymeth.2007.05.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2007] [Accepted: 05/01/2007] [Indexed: 10/22/2022] Open
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28
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Affiliation(s)
- Jean-Louis Mergny
- INSERM, U565, Acides Nucléiques: Dynamique, Ciblage et Fonctions Biologiques, 43 Rue Cuvier, CP26, Paris Cedex 05, 75231, France.
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29
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Gipson CL, Xin ZT, Danzy SC, Parslow TG, Ly H. Functional Characterization of Yeast Telomerase RNA Dimerization. J Biol Chem 2007; 282:18857-63. [PMID: 17491007 DOI: 10.1074/jbc.m700057200] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Telomerase is the cellular RNA-dependent DNA polymerase (i.e. reverse transcriptase) that uses an integral RNA template to synthesize telomeric DNA repeats at the ends of linear chromosomes. Human telomerase RNA (hTERC) is thought to function as a dimeric complex consisting of two RNAs that interact with each other physically as well as genetically. We show here for the first time that the yeast Saccharomyces cerevisiae telomerase RNA TLC1 likewise forms dimers in vitro. TLC1 dimerization depends on a unique 6-base self-complementary sequence, which closely mimics palindromic sequences that mediate functional dimerization of HIV-1 and other retroviral genomes. We found that dissimilar but comparably located TLC1 palindromes from other sensu stricto yeasts can functionally substitute for that of S. cerevisiae. Yeast cells expressing dimerization-defective TLC1 alleles have shorter telomeres than those with wild-type TLC1. This study, therefore, highlights dimerization as a functionally conserved feature of the RNA templates utilized by reverse transcriptases of both viral and cellular origins.
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Affiliation(s)
- Clay L Gipson
- Department of Pathology and Laboratory Medicine, Experimental Pathology Division, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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30
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Abstract
The structure and integrity of telomeres are essential for genome stability. Telomere dysregulation can lead to cell death, cell senescence, or abnormal cell proliferation. The maintenance of telomere repeats in most eukaryotic organisms requires telomerase, which consists of a reverse transcriptase (RT) and an RNA template that dictates the synthesis of the G-rich strand of telomere terminal repeats. Structurally, telomerase reverse transcriptase (TERT) contains unique and variable N- and C-terminal extensions that flank a central RT-like domain. The enzymology of telomerase includes features that are both similar to and distinct from those characteristic of other RTs. Two distinguishing features of TERT are its stable association with the telomerase RNA and its ability to repetitively reverse transcribe the template segment of RNA. Here we discuss TERT structure and function; its regulation by RNA-DNA, TERT-DNA, TERT-RNA, TERT-TERT interactions, and TERT-associated proteins; and the relationship between telomerase enzymology and telomere maintenance.
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Affiliation(s)
- Chantal Autexier
- Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, Quebec, Canada.
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31
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Legassie JD, Jarstfer MB. The unmasking of telomerase. Structure 2007; 14:1603-9. [PMID: 17098185 DOI: 10.1016/j.str.2006.09.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2006] [Revised: 09/01/2006] [Accepted: 09/08/2006] [Indexed: 12/15/2022]
Abstract
Telomerase is a ribonucleoprotein complex that reverse transcribes a portion of its RNA subunit during the synthesis of G-rich DNA at the 3' end of each chromosome in most eukaryotes. This activity compensates for the inability of the normal DNA replication machinery to fully replicate chromosome termini. The roles of telomerase in cellular immortality and tumor biology have catalyzed a significant interest in this unusual polymerase. Recently the first structures of two domains, the CR4/CR5 and pseudoknot, of human telomerase RNA (hTR) were reported, offering a structural basis for interpreting biochemical studies and possible roles of hTR mutations in human diseases. Structures of the stem II and stem IV domains of Tetrahymena thermophila TR as well as the N-terminal domain of the T. thermophila telomerase reverse transcriptase have also been determined. These studies complement previous biochemical studies, providing rich insight into the structural basis for telomerase activity.
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Affiliation(s)
- Jason D Legassie
- Division of Medicinal Chemistry and Natural Products, School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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32
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Gavory G, Symmons MF, Ghosh YK, Klenerman D, Balasubramanian S. Structural analysis of the catalytic core of human telomerase RNA by FRET and molecular modeling. Biochemistry 2006; 45:13304-11. [PMID: 17073451 PMCID: PMC2196208 DOI: 10.1021/bi061150a] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Telomerase is the ribonucleoprotein reverse transcriptase involved in the maintenance of the telomeres, the termini of eukaryotic chromosomes. The RNA component of human telomerase (hTR) consists of 451 nucleotides with the 5' half folding into a highly conserved catalytic core comprising the template region and an adjacent pseudoknot domain (nucleotides 1-208). While the secondary structure of hTR is established, there is little understanding of its three-dimensional (3D) architecture. Here, we have used fluorescence resonance energy transfer (FRET) between fluorescently labelled peptide nucleic acids, hybridized to defined single stranded regions of full length hTR, to evaluate long-range distances. Using molecular modeling, the distance constraints derived by FRET were subsequently used, together with the known secondary structure, to generate a 3D model of the catalytic core of hTR. An overlay of a large set of models generated has provided a low-resolution structure (6.5-8.0 A) that can readily be refined as new structural information becomes available. A notable feature of the modeled structure is the positioning of the template adjacent to the pseudoknot, which brings a number of conserved nucleotides close in space.
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Affiliation(s)
- Gérald Gavory
- University Chemical Laboratories, Lensfield Road, Cambridge CB2 1EW, U.K
| | - Martyn F. Symmons
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, U.K
| | | | - David Klenerman
- University Chemical Laboratories, Lensfield Road, Cambridge CB2 1EW, U.K
| | - Shankar Balasubramanian
- University Chemical Laboratories, Lensfield Road, Cambridge CB2 1EW, U.K
- To whom correspondence should be addressed. Tel: +44-1223-336347. Fax: +44-1223-336362. E-mail:
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33
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Abstract
Chromosome stability requires a dynamic balance of DNA loss and gain in each terminal tract of telomeric repeats. Repeat addition by a specialized reverse transcriptase, telomerase, has an important role in maintaining this equilibrium. Insights that have been gained into the cellular pathways for biogenesis and regulation of telomerase ribonucleoproteins raise new questions, particularly concerning the dynamic nature of this unique polymerase.
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Affiliation(s)
- Kathleen Collins
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3204, USA.
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34
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Shcherbakova DM, Zvereva ME, Shpanchenko OV, Dontsova OA. Telomerase: Structure and properties of the enzyme, and peculiarities of yeast telomerase. Mol Biol 2006. [DOI: 10.1134/s0026893306040042] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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35
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Chen Y, Fender J, Legassie JD, Jarstfer MB, Bryan TM, Varani G. Structure of stem-loop IV of Tetrahymena telomerase RNA. EMBO J 2006; 25:3156-66. [PMID: 16778765 PMCID: PMC1500990 DOI: 10.1038/sj.emboj.7601195] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2006] [Accepted: 05/15/2006] [Indexed: 12/21/2022] Open
Abstract
Conserved domains within the RNA component of telomerase provide the template for reverse transcription, recruit protein components to the holoenzyme and are required for enzymatic activity. Among the functionally essential domains in ciliate telomerase RNA is stem-loop IV, which strongly stimulates telomerase activity and processivity even when provided in trans. The NMR structure of Tetrahymena thermophila stem-loop IV shows a highly structured distal stem-loop linked to a conformationally flexible template-proximal region by a bulge that severely kinks the entire RNA. Through extensive structure-function studies, we identify residues that contribute to both these structural features and to enzymatic activity, with no apparent effect on the binding of TERT protein. We propose that the bending induced by the GA bulge and the flexibility of the template-proximal region allow positioning of the prestructured apical loop during the catalytic cycle.
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Affiliation(s)
- Yu Chen
- Department of Chemistry, University of Washington, Seattle WA, USA
| | - Jessica Fender
- Department of Chemistry, University of Washington, Seattle WA, USA
| | - Jason D Legassie
- Division of Medicinal Chemistry and Natural Products, University of North Carolina, Chapel Hill, NC, USA
| | - Michael B Jarstfer
- Division of Medicinal Chemistry and Natural Products, University of North Carolina, Chapel Hill, NC, USA
| | - Tracy M Bryan
- Children's Medical Research Institute, Westmead, NSW, Australia
| | - Gabriele Varani
- Department of Chemistry, University of Washington, Seattle WA, USA
- Department of Biochemistry, University of Washington, Seattle WA, USA
- Departments of Chemistry & Biochemistry, University of Washington, Box 351700, Seattle, WA 98185-1700, USA. Tel: +1 206 543 7113; Fax: +1 206 685 8665; E-mail:
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36
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Theimer CA, Feigon J. Structure and function of telomerase RNA. Curr Opin Struct Biol 2006; 16:307-18. [PMID: 16713250 DOI: 10.1016/j.sbi.2006.05.005] [Citation(s) in RCA: 155] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2006] [Revised: 04/25/2006] [Accepted: 05/08/2006] [Indexed: 12/21/2022]
Abstract
Maintenance of telomeres by the enzyme telomerase is essential for genomic stability and cell viability in ciliates, vertebrates and yeast. The minimal components of telomerase required for catalytic activity are the telomerase reverse transcriptase (TERT) protein and the template-containing telomerase RNA (TER). Recent studies have afforded significant advances in the biophysical characterization of telomerase RNAs from various species. The first TER structures have been reported, for regions of the catalytically essential pseudoknot and CR4/CR5 domains of human TER, and provide a structural basis for interpretation of mutational and biochemical data. The domains and interactions of the Tetrahymena thermophila telomerase holoenzyme RNA and protein components have been further characterized biochemically, and structures of the TER template boundary element and the N-terminal domain of T. thermophila TERT have been determined. Phylogenetic and biochemical analyses of yeast TERs have revealed core structural elements in common with ciliates and vertebrates, and the minimal domains required for function in vivo.
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Affiliation(s)
- Carla A Theimer
- Department of Chemistry and Biochemistry, and Molecular Biology Institute, University of California, Los Angeles, CA 90095-1569, USA
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37
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Jacobs SA, Podell ER, Cech TR. Crystal structure of the essential N-terminal domain of telomerase reverse transcriptase. Nat Struct Mol Biol 2006; 13:218-25. [PMID: 16462747 DOI: 10.1038/nsmb1054] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2005] [Accepted: 12/14/2005] [Indexed: 11/09/2022]
Abstract
Telomerase, a ribonucleoprotein enzyme, adds telomeric DNA repeats to the ends of linear chromosomes. Here we report the first high-resolution structure of any portion of the telomerase reverse transcriptase, the telomerase essential N-terminal (TEN) domain from Tetrahymena thermophila. The structure, which seems to represent a novel protein fold, shows phylogenetically conserved amino acid residues in a groove on its surface. These residues are crucial for telomerase catalytic activity, and several of them are required for sequence-specific binding of a single-stranded telomeric DNA primer. The positively charged C terminus, which becomes ordered upon interaction with other macromolecules, is involved in binding RNA in a non-sequence-specific manner. The TEN domain's ability to bind both RNA and telomeric DNA, coupled with the notably strong effects on activity upon mutagenesis of single surface residues, suggest how this domain contributes to telomerase catalysis.
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Affiliation(s)
- Steven A Jacobs
- Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA
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38
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Marie-Egyptienne DT, Cerone MA, Londoño-Vallejo JA, Autexier C. A human-Tetrahymena pseudoknot chimeric telomerase RNA reconstitutes a nonprocessive enzyme in vitro that is defective in telomere elongation. Nucleic Acids Res 2005; 33:5446-57. [PMID: 16192571 PMCID: PMC1236975 DOI: 10.1093/nar/gki848] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The phylogenetically-derived secondary structures of telomerase RNAs (TR) from ciliates, yeasts and vertebrates are surprisingly conserved and contain a pseudoknot domain at a similar location downstream of the template. As the pseudoknot domains of Tetrahymena TR (tTR) and human TR (hTR) mediate certain similar functions, we hypothesized that they might be functionally interchangeable. We constructed a chimeric TR (htTR) by exchanging the hTR pseudoknot sequences for the tTR pseudoknot region. The chimeric RNA reconstituted human telomerase activity when coexpressed with hTERT in vitro, but exhibited defects in repeat addition processivity and levels of DNA synthesis compared to hTR. Activity was dependent on tTR sequences within the chimeric RNA. htTR interacted with hTERT in vitro and dimerized predominantly via a region of its hTR backbone, the J7b/8a loop. Introduction of htTR in telomerase-negative cells stably expressing hTERT did not reconstitute an active enzyme able to elongate telomeres. Thus, our results indicate that the chimeric RNA reconstituted a weakly active nonprocessive human telomerase enzyme in vitro that was defective in telomere elongation in vivo. This suggests that there may be species-specific requirements for pseudoknot functions.
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Affiliation(s)
- Delphine T. Marie-Egyptienne
- Department of Anatomy and Cell Biology, Institut Curie26 rue d'Ulm, 75248 Paris, CEDEX 05, France
- Bloomfield Centre for Research in Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General HospitalMontréal, Québec, Canada H3T 1E2
| | - Maria Antonietta Cerone
- Department of Anatomy and Cell Biology, Institut Curie26 rue d'Ulm, 75248 Paris, CEDEX 05, France
- Bloomfield Centre for Research in Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General HospitalMontréal, Québec, Canada H3T 1E2
| | | | - Chantal Autexier
- Department of Anatomy and Cell Biology, Institut Curie26 rue d'Ulm, 75248 Paris, CEDEX 05, France
- Department of Medicine, McGill UniversityMontréal, Québec, Canada H3A 2B2
- Bloomfield Centre for Research in Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General HospitalMontréal, Québec, Canada H3T 1E2
- To whom correspondence should be addressed. Tel: +1 514 340 8260; Fax: +1 514 340 8295;
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39
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Cunningham DD, Collins K. Biological and biochemical functions of RNA in the tetrahymena telomerase holoenzyme. Mol Cell Biol 2005; 25:4442-54. [PMID: 15899850 PMCID: PMC1140614 DOI: 10.1128/mcb.25.11.4442-4454.2005] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Telomerase extends chromosome ends by the synthesis of tandem simple-sequence repeats. Studies of minimal recombinant telomerase ribonucleoprotein (RNP) reconstituted in vitro have revealed sequences within the telomerase RNA subunit (TER) that are required to establish its internal template and other unique features of enzyme activity. Here we test the significance of these motifs following TER assembly into telomerase holoenzyme in vivo. We established a method for stable expression of epitope-tagged TER and TER variants in place of wild-type Tetrahymena TER. We found that sequence substitutions in nontemplate regions of TER altered telomere length maintenance in vivo, with an increase or decrease in the set point for telomere length homeostasis. We also characterized the in vitro activity of the telomerase holoenzymes reconstituted with TER variants, following RNA-based RNP affinity purification from cell extracts. We found that nontemplate sequence substitutions imposed specific defects in the fidelity and processivity of template use. These findings demonstrate nontemplate functions of TER that are critical for the telomerase holoenzyme catalytic cycle and for proper telomere length maintenance in vivo.
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Affiliation(s)
- Doreen D Cunningham
- Department of Molecular and Cell Biology, 16 Barker Hall, University of California, Berkeley, CA 94720-3204, USA
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40
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Prathapam R, Witkin KL, O'Connor CM, Collins K. A telomerase holoenzyme protein enhances telomerase RNA assembly with telomerase reverse transcriptase. Nat Struct Mol Biol 2005; 12:252-7. [PMID: 15696174 PMCID: PMC2913471 DOI: 10.1038/nsmb900] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2004] [Accepted: 01/03/2005] [Indexed: 01/07/2023]
Abstract
Telomerase maintains the simple sequence repeats at chromosome ends, protecting cells from genomic rearrangement, proliferative senescence and death. The telomerase reverse transcriptase (TERT) and telomerase RNA (TER) alone can assemble into active enzyme in a heterologous cell extract, but the physiological process of telomerase biogenesis is more complex. The endogenous accumulation of Tetrahymena thermophila TERT and TER requires an additional telomerase holoenzyme protein, p65. Here, we reconstitute this cellular pathway for telomerase ribonucleoprotein biogenesis in vitro. We demonstrate that tandem RNA interaction domains in p65 recognize the sequence of the TER 3' stem. Notably, the p65-TER complex recruits TERT much more efficiently than does TER alone. Using bacterially expressed p65 and TERT polypeptides, we show that p65 enhances TERT-TER interaction by a mechanism involving a conserved bulge in the protein-bridging TER molecule. These findings reveal a pathway for telomerase holoenzyme biogenesis that preassembles TER for TERT recruitment.
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Affiliation(s)
- Ramadevi Prathapam
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA
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41
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Aigner S, Cech TR. The Euplotes telomerase subunit p43 stimulates enzymatic activity and processivity in vitro. RNA (NEW YORK, N.Y.) 2004; 10:1108-18. [PMID: 15208446 PMCID: PMC1370601 DOI: 10.1261/rna.7400704] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2004] [Accepted: 04/29/2004] [Indexed: 05/19/2023]
Abstract
Telomerase is a reverse transcriptase that synthesizes telomeric DNA repeats at the ends of eukaryotic chromosomes. Although it is minimally composed of a conserved catalytic protein subunit (TERT) and an RNA component, additional accessory factors present in the holoenzyme play crucial roles in the biogenesis and function of the enzyme complex. Telomerase from the ciliate Tetrahymena can be reconstituted in active form in vitro. Using this system, we show that p43, a telomerase-specific La-motif protein from the ciliate Euplotes, stimulates activity and increases repeat addition processivity of telomerase. Activity enhancement by p43 requires its incorporation into a TERT.RNA.p43 ternary complex but is independent of other dissociable protein factors functioning in telomerase complex assembly. Stimulation is enhanced at elevated temperatures, supporting a role for p43 in structural stabilization of a critical region of the RNA subunit. To our knowledge, this represents the first demonstration that an authentic telomerase accessory protein can directly affect the enzymatic activity of the core enzyme in vitro.
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Affiliation(s)
- Stefan Aigner
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA
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Moriarty TJ, Marie-Egyptienne DT, Autexier C. Functional organization of repeat addition processivity and DNA synthesis determinants in the human telomerase multimer. Mol Cell Biol 2004; 24:3720-33. [PMID: 15082768 PMCID: PMC387747 DOI: 10.1128/mcb.24.9.3720-3733.2004] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human telomerase is a multimer containing two human telomerase RNAs (hTRs) and most likely two human telomerase reverse transcriptases (hTERTs). Telomerase synthesizes multiple telomeric repeats using a unique repeat addition form of processivity. We investigated hTR and hTERT sequences that were essential for DNA synthesis and processivity using a direct primer extension telomerase assay. We found that hTERT consists of two physically separable functional domains, a polymerase domain containing RNA interaction domain 2 (RID2), reverse transcriptase (RT), and C-terminal sequences, and a major accessory domain, RNA interaction domain 1 (RID1). RID2 mutants defective in high-affinity hTR interactions and an RT catalytic mutant exhibited comparable DNA synthesis defects. The RID2-interacting hTR P6.1 helix was also essential for DNA synthesis. RID1 interacted with the hTR pseudoknot-template domain and hTERT's RT motifs and putative thumb and was essential for processivity, but not DNA synthesis. The hTR pseudoknot was essential for processivity, but not DNA synthesis, and processivity was reduced or abolished in dimerization-defective pseudoknot mutants. trans-acting hTERTs and hTRs complemented the processivity defects of RID1 and pseudoknot mutants, respectively. These data provide novel insight into the catalytic organization of the human telomerase complex and suggest that repeat addition processivity is one of the major catalytic properties conferred by telomerase multimerization.
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Affiliation(s)
- Tara J Moriarty
- Bloomfield Centre for Research in Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital and Department of Anatomy and Cell Biology, McGill University, Montréal, Québec, Canada
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43
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Abstract
In their 1985 Cell paper, Greider and Blackburn announced the discovery of an enzyme that extended the DNA at chromosome telomeres in the ciliate, Tetrahymena. Since then, there has been an explosion of knowledge about both the RNA and protein subunits of this unusual ribonucleoprotein enzyme in organisms ranging from the ciliates to yeast to humans. The regulation of telomerase is now understood to take place both at the level of synthesis of the enzyme and via the state of its substrate, the telomere itself. The roles of telomerase in both cellular immortality and cancer are vibrant areas of current research.
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Affiliation(s)
- Thomas R Cech
- Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309, USA.
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