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Lue NF, Autexier C. Orchestrating nucleic acid-protein interactions at chromosome ends: telomerase mechanisms come into focus. Nat Struct Mol Biol 2023; 30:878-890. [PMID: 37400652 PMCID: PMC10539978 DOI: 10.1038/s41594-023-01022-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Accepted: 05/16/2023] [Indexed: 07/05/2023]
Abstract
Telomerase is a special reverse transcriptase ribonucleoprotein dedicated to the synthesis of telomere repeats that protect chromosome ends. Among reverse transcriptases, telomerase is unique in using a stably associated RNA with an embedded template to synthesize a specified sequence. Moreover, it is capable of iteratively copying the same template region (repeat addition processivity) through multiple rounds of RNA-DNA unpairing and reannealing, that is, the translocation reaction. Biochemical analyses of telomerase over the past 3 decades in protozoa, fungi and mammals have identified structural elements that underpin telomerase mechanisms and have led to models that account for the special attributes of telomerase. Notably, these findings and models can now be interpreted and adjudicated through recent cryo-EM structures of Tetrahymena and human telomerase holoenzyme complexes in association with substrates and regulatory proteins. Collectively, these structures reveal the intricate protein-nucleic acid interactions that potentiate telomerase's unique translocation reaction and clarify how this enzyme reconfigures the basic reverse transcriptase scaffold to craft a polymerase dedicated to the synthesis of telomere DNA. Among the many new insights is the resolution of the telomerase 'anchor site' proposed more than 3 decades ago. The structures also highlight the nearly universal conservation of a protein-protein interface between an oligonucleotide/oligosaccharide-binding (OB)-fold regulatory protein and the telomerase catalytic subunit, which enables spatial and temporal regulation of telomerase function in vivo. In this Review, we discuss key features of the structures in combination with relevant functional analyses. We also examine conserved and divergent aspects of telomerase mechanisms as gleaned from studies in different model organisms.
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Affiliation(s)
- Neal F Lue
- Department of Microbiology and Immunology, Weill Cornell Medicine, New York, NY, USA.
| | - Chantal Autexier
- Lady Davis Institute for Medical Research, Jewish General Hospital and Department of Anatomy and Cell Biology and Department of Medicine, McGill University, Montreal, Quebec, Canada.
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2
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Zipper head mechanism of telomere synthesis by human telomerase. Cell Res 2021; 31:1275-1290. [PMID: 34782750 PMCID: PMC8648750 DOI: 10.1038/s41422-021-00586-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Accepted: 10/08/2021] [Indexed: 11/08/2022] Open
Abstract
Telomerase, a multi-subunit ribonucleoprotein complex, is a unique reverse transcriptase that catalyzes the processive addition of a repeat sequence to extend the telomere end using a short fragment of its own RNA component as the template. Despite recent structural characterizations of human and Tetrahymena telomerase, it is still a mystery how telomerase repeatedly uses its RNA template to synthesize telomeric DNA. Here, we report the cryo-EM structure of human telomerase holoenzyme bound with telomeric DNA at resolutions of 3.5 Å and 3.9 Å for the catalytic core and biogenesis module, respectively. The structure reveals that a leucine residue Leu980 in telomerase reverse transcriptase (TERT) catalytic subunit functions as a zipper head to limit the length of the short primer-template duplex in the active center. Moreover, our structural and computational analyses suggest that TERT and telomerase RNA (hTR) are organized to harbor a preformed active site that can accommodate short primer-template duplex substrates for catalysis. Furthermore, our findings unveil a double-fingers architecture in TERT that ensures nucleotide addition processivity of human telomerase. We propose that the zipper head Leu980 is a structural determinant for the sequence-based pausing signal of DNA synthesis that coincides with the RNA element-based physical template boundary. Functional analyses unveil that the non-glycine zipper head plays an essential role in both telomerase repeat addition processivity and telomere length homeostasis. In addition, we also demonstrate that this zipper head mechanism is conserved in all eukaryotic telomerases. Together, our study provides an integrated model for telomerase-mediated telomere synthesis.
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3
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Song J, Logeswaran D, Castillo-González C, Li Y, Bose S, Aklilu BB, Ma Z, Polkhovskiy A, Chen JJL, Shippen DE. The conserved structure of plant telomerase RNA provides the missing link for an evolutionary pathway from ciliates to humans. Proc Natl Acad Sci U S A 2019; 116:24542-24550. [PMID: 31754031 PMCID: PMC6900512 DOI: 10.1073/pnas.1915312116] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Telomerase is essential for maintaining telomere integrity. Although telomerase function is widely conserved, the integral telomerase RNA (TR) that provides a template for telomeric DNA synthesis has diverged dramatically. Nevertheless, TR molecules retain 2 highly conserved structural domains critical for catalysis: a template-proximal pseudoknot (PK) structure and a downstream stem-loop structure. Here we introduce the authentic TR from the plant Arabidopsis thaliana, called AtTR, identified through next-generation sequencing of RNAs copurifying with Arabidopsis TERT. This RNA is distinct from the RNA previously described as the templating telomerase RNA, AtTER1. AtTR is a 268-nt Pol III transcript necessary for telomere maintenance in vivo and sufficient with TERT to reconstitute telomerase activity in vitro. Bioinformatics analysis identified 85 AtTR orthologs from 3 major clades of plants: angiosperms, gymnosperms, and lycophytes. Through phylogenetic comparisons, a secondary structure model conserved among plant TRs was inferred and verified using in vitro and in vivo chemical probing. The conserved plant TR structure contains a template-PK core domain enclosed by a P1 stem and a 3' long-stem P4/5/6, both of which resemble a corresponding structural element in ciliate and vertebrate TRs. However, the plant TR contains additional stems and linkers within the template-PK core, allowing for expansion of PK structure from the simple PK in the smaller ciliate TR during evolution. Thus, the plant TR provides an evolutionary bridge that unites the disparate structures of previously characterized TRs from ciliates and vertebrates.
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Affiliation(s)
- Jiarui Song
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
| | | | | | - Yang Li
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287
| | - Sreyashree Bose
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
| | - Behailu Birhanu Aklilu
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
| | - Zeyang Ma
- National Maize Improvement Center of China, China Agricultural University, 100193 Beijing, China
- College of Agronomy and Biotechnology, China Agricultural University, 100193 Beijing, China
| | - Alexander Polkhovskiy
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
- Center of Life Sciences, Skolkovo Institute of Science and Technology, 121205 Moscow, Russian Federation
| | - Julian J-L Chen
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287;
| | - Dorothy E Shippen
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843;
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4
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Deshpande AP, Collins K. Mechanisms of template handling and pseudoknot folding in human telomerase and their manipulation to expand the sequence repertoire of processive repeat synthesis. Nucleic Acids Res 2018; 46:7886-7901. [PMID: 29986069 PMCID: PMC6125678 DOI: 10.1093/nar/gky601] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2018] [Accepted: 06/26/2018] [Indexed: 01/12/2023] Open
Abstract
Telomerase adds telomeric repeats to chromosome ends by processive copying of a template within the telomerase RNA bound to telomerase reverse transcriptase. Telomerase RNAs have single-stranded regions that separate the template from a 5' stem and 3' pseudoknot, and mammals gained additional stem P2a.1 separating the template from the pseudoknot. Using human telomerase, we show that the length of template 3'-flanking single-stranded RNA is a determinant of repeat addition processivity whereas template 5'-flanking single-stranded RNA and P2a.1 are critical for activity but not processivity. In comparison, requirements for the template sequence itself are confounding: different substitutions of the same position have strikingly different consequences, from improved processivity and activity to complete inactivation. We discovered that some altered-template sequences stabilize an alternative RNA conformation that precludes the pseudoknot by base-pairing of one pseudoknot strand to the template 3' end. Using mutations to reduce over-stability of the alternative conformation, we restore high activity and processivity to otherwise inactive altered-template telomerase ribonucleoproteins. In cells, over-stabilization or destabilization of the alternative state severely inhibited biogenesis of active telomerase. Our findings delineate roles for human telomerase RNA template-flanking regions, establish a biologically relevant pseudoknot-alternative RNA conformation, and expand the repertoire of human telomerase repeat synthesis.
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Affiliation(s)
- Aishwarya P Deshpande
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
| | - Kathleen Collins
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
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5
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Current Perspectives of Telomerase Structure and Function in Eukaryotes with Emerging Views on Telomerase in Human Parasites. Int J Mol Sci 2018; 19:ijms19020333. [PMID: 29364142 PMCID: PMC5855555 DOI: 10.3390/ijms19020333] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Revised: 01/10/2018] [Accepted: 01/17/2018] [Indexed: 12/11/2022] Open
Abstract
Replicative capacity of a cell is strongly correlated with telomere length regulation. Aberrant lengthening or reduction in the length of telomeres can lead to health anomalies, such as cancer or premature aging. Telomerase is a master regulator for maintaining replicative potential in most eukaryotic cells. It does so by controlling telomere length at chromosome ends. Akin to cancer cells, most single-cell eukaryotic pathogens are highly proliferative and require persistent telomerase activity to maintain constant length of telomere and propagation within their host. Although telomerase is key to unlimited cellular proliferation in both cases, not much was known about the role of telomerase in human parasites (malaria, Trypanosoma, etc.) until recently. Since telomerase regulation is mediated via its own structural components, interactions with catalytic reverse transcriptase and several factors that can recruit and assemble telomerase to telomeres in a cell cycle-dependent manner, we compare and discuss here recent findings in telomerase biology in cancer, aging and parasitic diseases to give a broader perspective of telomerase function in human diseases.
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Lai AG, Pouchkina-Stantcheva N, Di Donfrancesco A, Kildisiute G, Sahu S, Aboobaker AA. The protein subunit of telomerase displays patterns of dynamic evolution and conservation across different metazoan taxa. BMC Evol Biol 2017; 17:107. [PMID: 28441946 PMCID: PMC5405514 DOI: 10.1186/s12862-017-0949-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Accepted: 04/04/2017] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Most animals employ telomerase, which consists of a catalytic subunit known as the telomerase reverse transcriptase (TERT) and an RNA template, to maintain telomere ends. Given the importance of TERT and telomere biology in core metazoan life history traits, like ageing and the control of somatic cell proliferation, we hypothesised that TERT would have patterns of sequence and regulatory evolution reflecting the diverse life histories across the Animal Kingdom. RESULTS We performed a complete investigation of the evolutionary history of TERT across animals. We show that although TERT is almost ubiquitous across Metazoa, it has undergone substantial sequence evolution within canonical motifs. Beyond the known canonical motifs, we also identify and compare regions that are highly variable between lineages, but show conservation within phyla. Recent data have highlighted the importance of alternative splice forms of TERT in non-canonical functions and although animals may share some conserved introns, we find that the selection of exons for alternative splicing appears to be highly variable, and regulation by alternative splicing appears to be a very dynamic feature of TERT evolution. We show that even within a closely related group of triclad flatworms, where alternative splicing of TERT was previously correlated with reproductive strategy, we observe highly diverse splicing patterns. CONCLUSIONS Our work establishes that the evolutionary history and structural evolution of TERT involves previously unappreciated levels of change and the emergence of lineage specific motifs. The sequence conservation we describe within phyla suggests that these new motifs likely serve essential biological functions of TERT, which along with changes in splicing, underpin diverse functions of TERT important for animal life histories.
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Affiliation(s)
- Alvina G Lai
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
| | | | | | - Gerda Kildisiute
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK
| | - Sounak Sahu
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK
| | - A Aziz Aboobaker
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
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7
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Abstract
Telomerase is the eukaryotic solution to the ‘end-replication problem’ of linear chromosomes by synthesising the highly repetitive DNA constituent of telomeres, the nucleoprotein cap that protects chromosome termini. Functioning as a ribonucleoprotein (RNP) enzyme, telomerase is minimally composed of the highly conserved catalytic telomerase reverse transcriptase (TERT) and essential telomerase RNA (TR) component. Beyond merely providing the template for telomeric DNA synthesis, TR is an innate telomerase component and directly facilitates enzymatic function. TR accomplishes this by having evolved structural elements for stable assembly with the TERT protein and the regulation of the telomerase catalytic cycle. Despite its prominence and prevalence, TR has profoundly diverged in length, sequence, and biogenesis pathway among distinct evolutionary lineages. This diversity has generated numerous structural and mechanistic solutions for ensuring proper RNP formation and high fidelity telomeric DNA synthesis. Telomerase provides unique insights into RNA and protein coevolution within RNP enzymes.
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Affiliation(s)
- Joshua D Podlevsky
- a School of Molecular Sciences, Arizona State University , Tempe , AZ , USA
| | - Julian J-L Chen
- a School of Molecular Sciences, Arizona State University , Tempe , AZ , USA
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8
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Podlevsky JD, Li Y, Chen JJL. Structure and function of echinoderm telomerase RNA. RNA (NEW YORK, N.Y.) 2016; 22:204-215. [PMID: 26598712 PMCID: PMC4712671 DOI: 10.1261/rna.053280.115] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Accepted: 10/23/2015] [Indexed: 06/05/2023]
Abstract
Telomerase is a ribonucleoprotein (RNP) enzyme that requires an integral telomerase RNA (TR) subunit, in addition to the catalytic telomerase reverse transcriptase (TERT), for enzymatic function. The secondary structures of TRs from the three major groups of species, ciliates, fungi, and vertebrates, have been studied extensively and demonstrate dramatic diversity. Herein, we report the first comprehensive secondary structure of TR from echinoderms-marine invertebrates closely related to vertebrates-determined by phylogenetic comparative analysis of 16 TR sequences from three separate echinoderm classes. Similar to vertebrate TR, echinoderm TR contains the highly conserved template/pseudoknot and H/ACA domains. However, echinoderm TR lacks the ancestral CR4/5 structural domain found throughout vertebrate and fungal TRs. Instead, echinoderm TR contains a distinct simple helical region, termed eCR4/5, that is functionally equivalent to the CR4/5 domain. The urchin and brittle star eCR4/5 domains bind specifically to their respective TERT proteins and stimulate telomerase activity. Distinct from vertebrate telomerase, the echinoderm TR template/pseudoknot domain with the TERT protein is sufficient to reconstitute significant telomerase activity. This gain-of-function of the echinoderm template/pseudoknot domain for conferring telomerase activity presumably facilitated the rapid structural evolution of the eCR4/5 domain throughout the echinoderm lineage. Additionally, echinoderm TR utilizes the template-adjacent P1.1 helix as a physical template boundary element to prevent nontelomeric DNA synthesis, a mechanism used by ciliate and fungal TRs. Thus, the chimeric and eccentric structural features of echinoderm TR provide unparalleled insights into the rapid evolution of telomerase RNP structure and function.
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Affiliation(s)
- Joshua D Podlevsky
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, USA
| | - Yang Li
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, USA
| | - Julian J-L Chen
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, USA
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9
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Lee SS, Bohrson C, Pike AM, Wheelan SJ, Greider CW. ATM Kinase Is Required for Telomere Elongation in Mouse and Human Cells. Cell Rep 2015; 13:1623-32. [PMID: 26586427 PMCID: PMC4663052 DOI: 10.1016/j.celrep.2015.10.035] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Revised: 09/11/2015] [Accepted: 10/11/2015] [Indexed: 12/26/2022] Open
Abstract
Short telomeres induce a DNA damage response, senescence, and apoptosis, thus maintaining telomere length equilibrium is essential for cell viability. Telomerase addition of telomere repeats is tightly regulated in cells. To probe pathways that regulate telomere addition, we developed the ADDIT assay to measure new telomere addition at a single telomere in vivo. Sequence analysis showed telomerase-specific addition of repeats onto a new telomere occurred in just 48 hr. Using the ADDIT assay, we found that ATM is required for addition of new repeats onto telomeres in mouse cells. Evaluation of bulk telomeres, in both human and mouse cells, showed that blocking ATM inhibited telomere elongation. Finally, the activation of ATM through the inhibition of PARP1 resulted in increased telomere elongation, supporting the central role of the ATM pathway in regulating telomere addition. Understanding this role of ATM may yield new areas for possible therapeutic intervention in telomere-mediated disease.
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Affiliation(s)
- Stella Suyong Lee
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Predoctoral Training Program in Human Genetics and Molecular Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Craig Bohrson
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Alexandra Mims Pike
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Sarah Jo Wheelan
- Predoctoral Training Program in Human Genetics and Molecular Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA
| | - Carol Widney Greider
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Predoctoral Training Program in Human Genetics and Molecular Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA.
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10
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The putative Leishmania telomerase RNA (LeishTER) undergoes trans-splicing and contains a conserved template sequence. PLoS One 2014; 9:e112061. [PMID: 25391020 PMCID: PMC4229120 DOI: 10.1371/journal.pone.0112061] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2014] [Accepted: 10/11/2014] [Indexed: 02/07/2023] Open
Abstract
Telomerase RNAs (TERs) are highly divergent between species, varying in size and sequence composition. Here, we identify a candidate for the telomerase RNA component of Leishmania genus, which includes species that cause leishmaniasis, a neglected tropical disease. Merging a thorough computational screening combined with RNA-seq evidence, we mapped a non-coding RNA gene localized in a syntenic locus on chromosome 25 of five Leishmania species that shares partial synteny with both Trypanosoma brucei TER locus and a putative TER candidate-containing locus of Crithidia fasciculata. Using target-driven molecular biology approaches, we detected a ∼2,100 nt transcript (LeishTER) that contains a 5′ spliced leader (SL) cap, a putative 3′ polyA tail and a predicted C/D box snoRNA domain. LeishTER is expressed at similar levels in the logarithmic and stationary growth phases of promastigote forms. A 5′SL capped LeishTER co-immunoprecipitated and co-localized with the telomerase protein component (TERT) in a cell cycle-dependent manner. Prediction of its secondary structure strongly suggests the existence of a bona fide single-stranded template sequence and a conserved C[U/C]GUCA motif-containing helix II, representing the template boundary element. This study paves the way for further investigations on the biogenesis of parasite TERT ribonucleoproteins (RNPs) and its role in parasite telomere biology.
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11
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Abstract
Telomerase is a specialized reverse transcriptase (RT) containing an intrinsic telomerase RNA (TR) component. It synthesizes telomeric DNA repeats, (GGTTAG)n in humans, by reiteratively copying a precisely defined, short template sequence from the integral TR. The specific mechanism of how the telomerase active site uses this short template region accurately and efficiently during processive DNA repeat synthesis has remained elusive. Here we report that the human TR template, in addition to specifying the DNA sequence, is embedded with a single-nucleotide signal to pause DNA synthesis. After the addition of a dT residue to the DNA primer, which is specified by the 49 rA residue in the template, telomerase extends the DNA primer with three additional nucleotides and then pauses DNA synthesis. This sequence-defined pause site coincides precisely with the helix paired region 1 (P1)-defined physical template boundary and precludes the incorporation of nontelomeric nucleotides from residues outside the template region. Furthermore, this sequence-defined pausing mechanism is a key determinant, in addition to the P1-defined template boundary, for generating the characteristic 6-nt ladder banding pattern of telomeric DNA products in vitro. In the absence of the pausing signal, telomerase stalls nucleotide addition at multiple sites along the template, generating DNA products with heterogeneous terminal repeat registers. Our findings demonstrate that this unique self-regulating mechanism of the human TR template is essential for high-fidelity synthesis of DNA repeats.
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12
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Abstract
Telomerase adds simple-sequence repeats to the ends of linear chromosomes to counteract the loss of end sequence inherent in conventional DNA replication. Catalytic activity for repeat synthesis results from the cooperation of the telomerase reverse transcriptase protein (TERT) and the template-containing telomerase RNA (TER). TERs vary widely in sequence and structure but share a set of motifs required for TERT binding and catalytic activity. Species-specific TER motifs play essential roles in RNP biogenesis, stability, trafficking, and regulation. Remarkably, the biogenesis pathways that generate mature TER differ across eukaryotes. Furthermore, the cellular processes that direct the assembly of a biologically functional telomerase holoenzyme and its engagement with telomeres are evolutionarily varied and regulated. This review highlights the diversity of strategies for telomerase RNP biogenesis, RNP assembly, and telomere recruitment among ciliates, yeasts, and vertebrates and suggests common themes in these pathways and their regulation.
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Affiliation(s)
- Emily D. Egan
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720-3200, USA
| | - Kathleen Collins
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720-3200, USA
- Corresponding authorE-mail
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13
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Goldin S, Kertesz Rosenfeld K, Manor H. Tracing the path of DNA substrates in active Tetrahymena telomerase holoenzyme complexes: mapping of DNA contact sites in the RNA subunit. Nucleic Acids Res 2012; 40:7430-41. [PMID: 22584626 PMCID: PMC3424564 DOI: 10.1093/nar/gks416] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Telomerase, the enzyme that extends single-stranded telomeric DNA, consists of an RNA subunit (TER) including a short template sequence, a catalytic protein (TERT) and accessory proteins. We used site-specific UV cross-linking to map the binding sites for DNA primers in TER within active Tetrahymena telomerase holoenzyme complexes. The mapping was performed at single-nucleotide resolution by a novel technique based on RNase H digestion of RNA–DNA hybrids made with overlapping complementary oligodeoxynucleotides. These data allowed tracing of the DNA path through the telomerase complexes from the template to the TERT binding element (TBE) region of TER. TBE is known to bind TERT and to be involved in the template 5′-boundary definition. Based on these findings, we propose that upstream sequences of each growing telomeric DNA chain are involved in regulation of its growth arrest at the 5′-end of the RNA template. The upstream DNA–TBE interaction may also function as an anchor for the subsequent realignment of the 3′-end of the DNA with the 3′-end of the template to enable initiation of synthesis of a new telomeric repeat.
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Affiliation(s)
- Svetlana Goldin
- Department of Biology, Technion-Israel Institute of Technology, Haifa 32 000, Israel
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14
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Berman AJ, Akiyama BM, Stone MD, Cech TR. The RNA accordion model for template positioning by telomerase RNA during telomeric DNA synthesis. Nat Struct Mol Biol 2011; 18:1371-5. [PMID: 22101935 PMCID: PMC3230705 DOI: 10.1038/nsmb.2174] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2011] [Accepted: 10/07/2011] [Indexed: 12/27/2022]
Abstract
Telomerase is a ribonucleoprotein (RNP) enzyme that maintains the ends of linear eukaryotic chromosomes and whose activation is a hallmark of 90% of all cancers. This RNP minimally contains a reverse transcriptase protein subunit (TERT) that catalyzes telomeric DNA synthesis and an RNA subunit (TER) that has templating, architectural and protein-scaffolding roles. Telomerase is unique among polymerases in that it synthesizes multiple copies of the template on the 3′ end of a primer following a single binding event, a process known as repeat addition processivity (RAP). Using biochemical assays and single-molecule Förster resonance energy transfer (smFRET) experiments on Tetrahymena thermophila telomerase, we now directly demonstrate that TER contributes to template positioning within the active site and to the template translocation required for RAP. We propose that the single-stranded RNA elements flanking the template act as a molecular accordion, undergoing reciprocal extension and compaction during telomerase translocation.
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Affiliation(s)
- Andrea J Berman
- Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Colorado, Boulder, Colorado, USA
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15
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Tetrahymena telomerase protein p65 induces conformational changes throughout telomerase RNA (TER) and rescues telomerase reverse transcriptase and TER assembly mutants. Mol Cell Biol 2010; 30:4965-76. [PMID: 20713447 DOI: 10.1128/mcb.00827-10] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The biogenesis of the Tetrahymena telomerase ribonucleoprotein particle (RNP) is enhanced by p65, a La family protein. Single-molecule and biochemical studies have uncovered a hierarchical assembly of the RNP, wherein the binding of p65 to stems I and IV of telomerase RNA (TER) causes a conformational change that facilitates the subsequent binding of telomerase reverse transcriptase (TERT) to TER. We used purified p65 and variants of TERT and TER to investigate the conformational rearrangements that occur during RNP assembly. Nuclease protection assays and mutational analysis revealed that p65 interacts with and stimulates conformational changes in regions of TER beyond stem IV. Several TER mutants exhibited telomerase activity only in the presence of p65, revealing the importance of p65 in promoting the correct RNP assembly pathway. In addition, p65 rescued TERT assembly mutants but not TERT activity mutants. Taken together, these results suggest that p65 stimulates telomerase assembly and activity in two ways. First, by sequestering stems I and IV, p65 limits the ensemble of structural conformations of TER, thereby presenting TERT with the active conformation of TER. Second, p65 acts as a molecular buttress within the assembled RNP, mutually stabilizing TER and TERT in catalytically active conformations.
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16
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Fakhoury J, Marie-Egyptienne DT, Londoño-Vallejo JA, Autexier C. Telomeric function of mammalian telomerases at short telomeres. J Cell Sci 2010; 123:1693-704. [PMID: 20427319 DOI: 10.1242/jcs.063636] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Telomerase synthesizes telomeric sequences and is minimally composed of a reverse transcriptase (RT) known as TERT and an RNA known as TR. We reconstituted heterologous mouse (m) and human (h) TERT-TR complexes and chimeric mTERT-hTERT-hTR complexes in vitro and in immortalized human alternative lengthening of telomere (ALT) cells. Our data suggest that species-specific determinants of activity, processivity and telomere function map not only to the TR but also to the TERT component. The presence of hTERT-hTR, but not heterologous TERT-TR complexes or chimeric mTERT-hTERT-hTR complexes, significantly reduced the percentage of chromosomes without telomeric signals in ALT cells. Moreover, heterologous and chimeric complexes were defective in recruitment to telomeres. Our results suggest a requirement for several hTERT domains and interaction with multiple proteins for proper recruitment of telomerase to the shortest telomeres in human ALT cells. Late-passage mTERT(-/-) mouse embryonic stem (ES) cells ectopically expressing hTERT or mTERT harboured fewer chromosome ends without telomeric signals and end-to-end fusions than typically observed in late-passage mTERT(-/-) ES cells. The ability of hTERT to function at mouse telomeres and the inability of mTERT to function at human telomeres suggest that mechanisms regulating the recruitment and activity of hTERT at mouse telomeres might be less stringent than the mechanisms regulating mTERT at human telomeres.
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Affiliation(s)
- Johans Fakhoury
- Bloomfield Center for Research in Aging, Lady Davis Institute, Jewish General Hospital, 3755 Côte Ste-Catherine Road, Montreal QC, Canada H3T 1E2
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17
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Structural basis for telomerase catalytic subunit TERT binding to RNA template and telomeric DNA. Nat Struct Mol Biol 2010; 17:513-8. [PMID: 20357774 DOI: 10.1038/nsmb.1777] [Citation(s) in RCA: 146] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2009] [Accepted: 01/20/2010] [Indexed: 12/17/2022]
Abstract
Telomerase is a specialized DNA polymerase that extends the 3' ends of eukaryotic linear chromosomes, a process required for genomic stability and cell viability. Here we present the crystal structure of the active Tribolium castaneum telomerase catalytic subunit, TERT, bound to an RNA-DNA hairpin designed to resemble the putative RNA-templating region and telomeric DNA. The RNA-DNA hybrid adopts a helical structure, docked in the interior cavity of the TERT ring. Contacts between the RNA template and motifs 2 and B' position the solvent-accessible RNA bases close to the enzyme active site for nucleotide binding and selectivity. Nucleic acid binding induces rigid TERT conformational changes to form a tight catalytic complex. Overall, TERT-RNA template and TERT-telomeric DNA associations are remarkably similar to those observed for retroviral reverse transcriptases, suggesting common mechanistic aspects of DNA replication between the two families of enzymes.
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18
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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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19
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20
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Box JA, Bunch JT, Zappulla DC, Glynn EF, Baumann P. A flexible template boundary element in the RNA subunit of fission yeast telomerase. J Biol Chem 2008; 283:24224-33. [PMID: 18574244 DOI: 10.1074/jbc.m802043200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Telomerase adds telomeric repeat sequences to chromosome ends using a short region of its RNA subunit as a template. Telomerase RNA subunits are phylogenetically highly divergent, and different strategies have evolved to demarcate the boundary of the template region. The recent identification of the gene encoding telomerase RNA in the fission yeast Schizosaccharomyces pombe (ter1+) has opened the door for structure-function analyses in a model that shares many features with the telomere maintenance machinery of higher eukaryotes. Here we describe a structural element in TER1 that defines the 5' boundary of the template. Disruption of a predicted long range base pairing interaction between template-adjacent nucleotides and a sequence further upstream resulted in reverse transcription beyond the template region and caused telomere shortening. Normal telomere length was restored by combining complementary nucleotide substitutions in both elements, showing that base pairing, not a specific sequence, limits reverse transcription beyond the template. The template boundary described here resembles that of budding yeasts and some mammalian telomerases. However, unlike any previously characterized boundary element, part of the paired region overlaps with the template itself, thus necessitating disruption of these interactions during most reverse transcription cycles. We show that changes in the paired region directly affect the length of individual telomeric repeat units. Our data further illustrate that marginal alignment of the telomeric 3' end with RNA sequences downstream of the template is responsible for primer slippage, causing incorporation of strings of guanosines at the start of a subset of repeats.
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Affiliation(s)
- Jessica A Box
- Stowers Institute for Medical Research, 1000 East 50th Street, Kansas City, MO 64110, USA
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21
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Chakrabarti K, Pearson M, Grate L, Sterne-Weiler T, Deans J, Donohue JP, Ares M. Structural RNAs of known and unknown function identified in malaria parasites by comparative genomics and RNA analysis. RNA (NEW YORK, N.Y.) 2007; 13:1923-39. [PMID: 17901154 PMCID: PMC2040097 DOI: 10.1261/rna.751807] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
As the genomes of more eukaryotic pathogens are sequenced, understanding how molecular differences between parasite and host might be exploited to provide new therapies has become a major focus. Central to cell function are RNA-containing complexes involved in gene expression, such as the ribosome, the spliceosome, snoRNAs, RNase P, and telomerase, among others. In this article we identify by comparative genomics and validate by RNA analysis numerous previously unknown structural RNAs encoded by the Plasmodium falciparum genome, including the telomerase RNA, U3, 31 snoRNAs, as well as previously predicted spliceosomal snRNAs, SRP RNA, MRP RNA, and RNAse P RNA. Furthermore, we identify six new RNA coding genes of unknown function. To investigate the relationships of the RNA coding genes to other genomic features in related parasites, we developed a genome browser for P. falciparum (http://areslab.ucsc.edu/cgi-bin/hgGateway). Additional experiments provide evidence supporting the prediction that snoRNAs guide methylation of a specific position on U4 snRNA, as well as predicting an snRNA promoter element particular to Plasmodium sp. These findings should allow detailed structural comparisons between the RNA components of the gene expression machinery of the parasite and its vertebrate hosts.
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Affiliation(s)
- Kausik Chakrabarti
- Department of Molecular, Cell and Developmental Biology, Center for Molecular Biology of RNA, University of California at Santa Cruz, Santa Cruz, CA 95064, USA
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22
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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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23
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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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24
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Richards RJ, Wu H, Trantirek L, O'Connor CM, Collins K, Feigon J. Structural study of elements of Tetrahymena telomerase RNA stem-loop IV domain important for function. RNA (NEW YORK, N.Y.) 2006; 12:1475-85. [PMID: 16809815 PMCID: PMC1524899 DOI: 10.1261/rna.112306] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Tetrahymena telomerase RNA (TER) contains several regions in addition to the template that are important for function. Central among these is the stem-loop IV domain, which is involved in both catalysis and RNP assembly, and includes binding sites for both the holoenzyme assembly protein p65 and telomerase reverse transcriptase (TERT). Stem-loop IV contains two regions with high evolutionary sequence conservation: a central GA bulge between helices, and a terminal loop. We solved the solution structure of loop IV and modeled the structure of the helical region containing the GA bulge, using NMR and residual dipolar couplings. The central GA bulge with flanking C-G base pairs induces a approximately 50 degrees semi-rigid bend in the helix. Loop IV is highly structured, and contains a conserved C-U base pair at the top of the helical stem. Analysis of new and previous biochemical data in light of the structure provides a rationale for some of the sequence conservation in this region of TER. The results suggest that during holoenzyme assembly the protein p65 recognizes a bend in stem IV, and this binding to central stem IV helps to position the structured loop IV for interaction with TERT and other region(s) of TER.
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Affiliation(s)
- Rebecca J Richards
- Department of Molecular Biology and Biochemistry, University of South Bohemia, Czech Republic
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25
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Richards RJ, Theimer CA, Finger LD, Feigon J. Structure of the Tetrahymena thermophila telomerase RNA helix II template boundary element. Nucleic Acids Res 2006; 34:816-25. [PMID: 16452301 PMCID: PMC1360744 DOI: 10.1093/nar/gkj481] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Telomere addition by telomerase requires an internal templating sequence located in the RNA subunit of telomerase. The correct boundary definition of this template sequence is essential for the proper addition of the nucleotide repeats. Incorporation of incorrect telomeric repeats onto the ends of chromosomes has been shown to induce chromosomal instability in ciliate, yeast and human cells. A 5′ template boundary defining element (TBE) has been identified in human, yeast and ciliate telomerase RNAs. Here, we report the solution structure of the TBE element (helix II) from Tetrahymena thermophila telomerase RNA. Our results indicate that helix II and its capping pentaloop form a well-defined structure including unpaired, stacked adenine nucleotides in the stem and an unusual syn adenine nucleotide in the loop. A comparison of the T.thermophila helix II pentaloop with a pentaloop of the same sequence found in the 23S rRNA of the Haloarcula marismortui ribosome suggests possible RNA and/or protein interactions for the helix II loop within the Tetrahymena telomerase holoenzyme.
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Affiliation(s)
- Rebecca J. Richards
- Department of Chemistry and Biochemistry, University of CaliforniaLos Angeles, CA 90095-1569, USA
| | - Carla A. Theimer
- Department of Chemistry and Biochemistry, University of CaliforniaLos Angeles, CA 90095-1569, USA
| | - L. David Finger
- Department of Chemistry and Biochemistry, University of CaliforniaLos Angeles, CA 90095-1569, USA
| | - Juli Feigon
- Department of Chemistry and Biochemistry, University of CaliforniaLos Angeles, CA 90095-1569, USA
- Molecular Biology Institute, University of CaliforniaLos Angeles, CA 90095-1569, USA
- To whom correspondence should be addressed. Tel: +1 310 206 6922; Fax: +1 310 825 0982;
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26
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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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27
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O’Connor CM, Lai CK, Collins K. Two purified domains of telomerase reverse transcriptase reconstitute sequence-specific interactions with RNA. J Biol Chem 2005; 280:17533-9. [PMID: 15731105 PMCID: PMC2917599 DOI: 10.1074/jbc.m501211200] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Telomerase reverse transcriptase (TERT) and telomerase RNA (TER) function together to create a uniquely specialized polymerase. Here we have described for the first time domains of bacterially expressed Tetrahymena TERT that interacted directly with TER in the absence of assembly chaperones. We used quantitative binding assays to define TER sequence requirements for recognition by the high affinity RNA binding domain and an independent N-terminal RNA interaction domain. The TERT RNA binding domain and N-terminal RNA interaction domain had distinct, nonoverlapping requirements for TER sequence and structure that together accounted for all of the sites of TER contact inferred for full-length TERT. The TER residues important for TERT binding are only a subset of the residues required for catalytic activity. Our findings demonstrate telomerase functional specialization by an elaborate ribonucleoprotein architecture physically separable from the active site.
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Affiliation(s)
- Catherine M. O’Connor
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3204
| | | | - Kathleen Collins
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3204
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28
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Affiliation(s)
- Jiunn-Liang Chen
- Department of Chemistry and Biochemistry and School of Life Sciences, Arizona State University, Tempe, AZ 85287-1604, USA.
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29
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Rivera MA, Blackburn EH. Processive utilization of the human telomerase template: lack of a requirement for template switching. J Biol Chem 2004; 279:53770-81. [PMID: 15456773 DOI: 10.1074/jbc.m407768200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ribonucleoprotein telomerase is a specialized reverse transcriptase minimally composed of an RNA, TER, and a protein catalytic subunit, TERT. The TER and TERT subunits of telomerase associate to form a dimeric enzyme in several organisms, including human. A small portion of TER, the template domain, is used by telomerase for the synthesis of tandem repeats of telomeric DNA. We studied some of the requirements for processive template usage by human telomerase. A blunt-ended duplex DNA primer was not utilized by telomerase. With a duplex telomeric DNA primer, a single-stranded 3' overhang with a minimum length of approximately 6 bases was required for efficient priming activity. Large substitutions in the human TER templating domain did not abolish enzymatic activity, although insertion of two residues into this sequence reduced processivity, as did a template mutation that results in a mismatch between the template region used for copying DNA and the region used for alignment of the substrate primer. Finally, by using a complementary pair of catalytically inactive telomerase RNA pseudoknot mutants in combination with a marked template, we demonstrated that processive synthesis by an obligatory dimer of human telomerase does not require template switching. These results indicate that processive template usage by human telomerase, like that of Tetrahymena telomerase, is strongly dependent on the base identities in the template domain and that a dimeric human telomerase can processively utilize a single template.
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Affiliation(s)
- Melissa A Rivera
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143-2200, USA
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30
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Chen JL, Greider CW. Telomerase RNA structure and function: implications for dyskeratosis congenita. Trends Biochem Sci 2004; 29:183-92. [PMID: 15082312 DOI: 10.1016/j.tibs.2004.02.003] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Jiunn-Liang Chen
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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31
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Abstract
Telomerase uses a short template sequence in its intrinsic RNA component to synthesize telomere repeats. Disruption of the helix P1b in human telomerase RNA or alteration of its distance from the template resulted in telomerase copying residues past the normal template boundary both in vivo and in vitro. Therefore, helix P1b is important for template boundary definition in human telomerase. Mouse telomerase RNA lacks helix P1b, and the boundary is established at 2 nt downstream of the 5'-end. The divergent structure of boundary definition elements in mammals, yeast, and ciliates suggests diverse mechanisms for template boundary definition in telomerase.
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Affiliation(s)
- Jiunn-Liang Chen
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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32
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Mason DX, Goneska E, Greider CW. Stem-loop IV of tetrahymena telomerase RNA stimulates processivity in trans. Mol Cell Biol 2003; 23:5606-13. [PMID: 12897134 PMCID: PMC166324 DOI: 10.1128/mcb.23.16.5606-5613.2003] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Telomerase is a ribonucleoprotein enzyme responsible for the addition of telomeres onto the ends of chromosomes. Short or dysfunctional telomeres can lead to cell growth arrest, apoptosis, and genomic instability. Telomerase uses its RNA subunit to copy a short template region for telomere synthesis. To probe for regions of Tetrahymena telomerase RNA essential for function, we assayed 27 circularly permuted RNA deletions for telomerase in vitro activity and binding to the telomerase reverse transcriptase catalytic protein subunit. We found that stem-loop IV is required for wild-type telomerase activity in vitro and will stimulate processivity when added in trans.
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Affiliation(s)
- Douglas X Mason
- Department of Molecular Biology and Genetics, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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33
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Huard S, Moriarty TJ, Autexier C. The C terminus of the human telomerase reverse transcriptase is a determinant of enzyme processivity. Nucleic Acids Res 2003; 31:4059-70. [PMID: 12853623 PMCID: PMC165952 DOI: 10.1093/nar/gkg437] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The catalytic subunit of telomerase (TERT) contains conserved reverse transcriptase-like motifs but N- and C-terminal regions unique to telomerases. Despite weak sequence conservation, the C terminus of TERTs from various organisms has been implicated in telomerase-specific functions, including telomerase activity, functional multimerization with other TERT molecules, enzyme processivity and telomere length maintenance. We studied hTERT proteins containing small C-terminal deletions or substitutions to identify and characterize hTERT domains mediating telomerase activity, hTERT multimerization and processivity. Using sequence alignment of five vertebrate TERTs and Arabidopsis thaliana TERT, we identified blocks of highly conserved amino acids that were required for human telomerase activity and functional hTERT complementation. We adapted the non-PCR-based telomerase elongation assay to characterize telomerase expressed and reconstituted in the in vitro transcription/translation rabbit reticulocyte lysate system. Using this assay, we found that the hTERT C terminus, like the C terminus of Saccharomyces cerevisiae TERT, contributes to successive nucleotide addition within a single 6-base telomeric repeat (type I processivity). Certain mutations in the hTERT C terminus also reduced the repetitive addition of multiple telomeric repeats (type II processivity). Our results suggest a functionally conserved role for the TERT C terminus in telomerase enzyme processivity.
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Affiliation(s)
- Sylvain Huard
- Department of Anatomy and Cell Biology, McGill University, Montréal, Québec, Canada, H3A 2B4
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34
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Abstract
Arthur Kornberg "never met a dull enzyme" (For the Love of Enzymes: The Odyssey of a Biochemist, Harvard University Press, 1989) and telomerase is no exception. Telomerase is a remarkable polymerase that uses an internal RNA template to reverse-transcribe telomere DNA, one nucleotide at a time, onto telomeric, G-rich single-stranded DNA. In the 17 years since its discovery, the characterization of telomerase enzyme components has uncovered a highly conserved family of telomerase reverse transcriptases that, together with the telomerase RNA, appear to comprise the enzymatic core of telomerase. While not as comprehensively understood as yet, some telomerase-associated proteins also serve crucial roles in telomerase function in vivo, such as telomerase ribonudeoprotein (RNP) assembly, recruitment to the telomere, and the coordination of DNA replication at the telomere. A selected overview of the biochemical properties of this unique enzyme, in vitro and in vivo, will be presented.
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35
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Petcherskaia M, McGuire JM, Pherson JM, Kirk KE. Loss of cap structure causes mitotic defect in Tetrahymena thermophila telomerase mutants. Chromosoma 2003; 111:429-37. [PMID: 12707780 DOI: 10.1007/s00412-003-0233-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2002] [Revised: 12/16/2002] [Accepted: 12/16/2002] [Indexed: 11/30/2022]
Abstract
Mutation of the telomeric repeat sequence has severe cellular consequences in a variety of systems. A Tetrahymena thermophila telomerase template mutant, ter1-43AA, displays an acute mitotic chromosome segregation defect. In the study described here we investigated the molecular basis for this lethality. Although cloned ter1-43AA macronuclear telomeres had long tracts of wild-type G4T2 repeats, they were capped by a mixture of G4T3 repeats, shown previously to be non-lethal, and G4T4 repeats, the telomeric sequence normally found in hypotrichous ciliates such as Oxytricha. To test further the functionality of the G4T4 repeat sequence in T. thermophila, we devised a new template mutation, ter1-44+AA, that resulted in more uniform synthesis of this sequence at telomere caps in vivo. The ter1-44+AA mutant displayed the most severe mitotic defect reported to date, with up to 85% of the population having micronuclei in anaphase, providing firm evidence that the hypotrich repeat sequence is not functional in Tetrahymena. Surprisingly, in spite of the telomeric sequence mutation, neither the ter1-43AA nor ter1-44+AA mutant displayed any significant loss of telomere length regulation. These results demonstrate that loss of telomere cap integrity, rather than length regulation, leads to the anaphase defect.
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36
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Förstemann K, Zaug AJ, Cech TR, Lingner J. Yeast telomerase is specialized for C/A-rich RNA templates. Nucleic Acids Res 2003; 31:1646-55. [PMID: 12626706 PMCID: PMC152863 DOI: 10.1093/nar/gkg261] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Telomeres, the protective caps of eukaryotic chromosomes, are maintained by the enzyme telomerase. This telomere-specific reverse transcriptase (RT) uses a small region of its RNA subunit as template to synthesize telomeric DNA, which is generally G/T rich in the strand that contains the 3' end. To further our understanding of why telomeres are usually G/T rich, we screened Saccharomyces cerevisiae telomerase RNA (TLC1) libraries with randomized template sequences for complementation of a tlc1 deletion and decapping of existing telomeres. Surprisingly, the vast majority of the 60 000 different mutant telomerase templates tested showed no activity in vivo. This deficiency was not due to impaired assembly with the catalytic subunit (Est2p) nor could it be alleviated by enforced telomerase recruitment to the telomeres. Rather, the mutant templates reduced the nucleotide addition processivity of telomerase. The functional RNA template sequences recovered in our screens preferentially contained two or more consecutive rC nucleotides, reminiscent of the wild-type template. Thus, in contrast to retroviral RTs that can reverse transcribe any RNA sequence into DNA, the budding yeast telomerase RT is specialized for its C-rich RNA template.
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Affiliation(s)
- Klaus Förstemann
- Swiss Institute for Experimental Cancer Research (ISREC), Chemin des Boveresses 155, CH-1066 Epalinges, Switzerland
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37
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Chen JL, Greider CW. Determinants in mammalian telomerase RNA that mediate enzyme processivity and cross-species incompatibility. EMBO J 2003; 22:304-14. [PMID: 12514136 PMCID: PMC140099 DOI: 10.1093/emboj/cdg024] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Telomerase contains two essential components: an RNA molecule that templates telomeric repeat synthesis and a catalytic protein component. Human telomerase is processive, while the mouse enzyme has much lower processivity. We have identified nucleotide determinants in the telomerase RNA that are responsible for this difference in processivity. Mutations adjacent to the template region of human and mouse telomerase RNA significantly altered telomerase processivity both in vitro and in vivo. We also identified functionally important nucleotides in the pseudoknot domain of telomerase RNA that potentially mediate the incompatibility between human TERT and mouse telomerase RNA. These experiments identify essential residues of the telomerase RNA that regulate telomerase activity and processivity.
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Affiliation(s)
- Jiunn-Liang Chen
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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38
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Gavory G, Farrow M, Balasubramanian S. Minimum length requirement of the alignment domain of human telomerase RNA to sustain catalytic activity in vitro. Nucleic Acids Res 2002; 30:4470-80. [PMID: 12384594 PMCID: PMC137139 DOI: 10.1093/nar/gkf575] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Telomeres are essential for genomic stability and cell viability. Telomerase, the enzyme responsible for telomere maintenance, is composed of a reverse transcriptase protein subunit and an integral RNA component which contains the templating domain. In human telomerase, the template region consists of 11 nt (3'-rCAAUCCCAAUC-5') and comprises an alignment domain (italicised) plus a template sequence encoding the telomeric repeat d(GGT TAG). In this study, the alignment domain of human telomerase was systematically reduced from the 3' end and the resultant recombinant enzyme activity was evaluated in vitro. Deletion or substitution of one or two residues from the 3' end of the alignment domain caused only a slight reduction in overall catalytic activity and did not alter the processivity of the enzyme. Deletion or substitution of three or more residues from the 3' end of the alignment domain resulted in total loss of catalytic activity. These results suggest that the two most 3' terminal RNA residues are relevant but not essential for overall activity and that the minimal length requirement of the alignment domain is 3 nt. Furthermore, base pairing between the 3' end of the primer substrate and the first two residues of the alignment domain is also not an absolute requirement for processive synthesis.
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Affiliation(s)
- Gérald Gavory
- University Chemical Laboratory, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK
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Miller MC, Collins K. Telomerase recognizes its template by using an adjacent RNA motif. Proc Natl Acad Sci U S A 2002; 99:6585-90. [PMID: 11997465 PMCID: PMC124446 DOI: 10.1073/pnas.102024699] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Telomerase adds telomeric repeats to chromosome 3' ends, forestalling the cellular senescence, apoptosis, and genomic instability that result from telomere loss caused by incomplete DNA replication. The telomerase ribonucleoprotein is dedicated to synthesis of tandem, simple-sequence repeats by virtue of its specialization for copying only a specific template region within the integral RNA. Here, using circularly permuted variants of Tetrahymena thermophila telomerase RNA, we identify the features that allow recognition of the template region within the RNA. We engineered a template-less telomerase ribonucleoprotein that can position and reverse transcribe an exchangeable RNA oligonucleotide template accurately. Only a short "template-recognition" element sequence tag is required to direct efficient use of adjacent 5' residues as a template for telomeric repeat synthesis. Our findings reveal molecular requirements for template selection by telomerase and physically resolve templating from other RNA functions in catalysis.
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Affiliation(s)
- Michael C Miller
- Department of Molecular and Cell Biology, University of California, 401 Barker Hall, Berkeley, CA 94720-3204, USA
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40
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Abstract
Telomerase elongates chromosome ends by addition of telomeric DNA repeats. The telomerase ribonucleoprotein can copy only a short template sequence within the telomerase RNA subunit. Here, we identify a region of telomerase RNA that is necessary for both correct 5' template boundary definition and high affinity telomerase reverse transcriptase (TERT) interaction. We also demonstrate that TERT mutants in the RNA binding domain compromise both 5' boundary definition and RNA binding. Our results indicate that sequence-specific interaction of a telomerase RNA element with the TERT RNA binding domain, not the active site motifs, defines the template boundary.
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Affiliation(s)
- Cary K Lai
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3204, USA
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41
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Bachand F, Autexier C. Functional regions of human telomerase reverse transcriptase and human telomerase RNA required for telomerase activity and RNA-protein interactions. Mol Cell Biol 2001; 21:1888-97. [PMID: 11238925 PMCID: PMC86762 DOI: 10.1128/mcb.21.5.1888-1897.2001] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Telomerase is a specialized reverse transcriptase (RT) that is minimally composed of a protein catalytic subunit and an RNA component. The RNA subunit contains a short template sequence that directs the synthesis of DNA repeats at the ends of chromosomes. Human telomerase activity can be reconstituted in vitro by the expression of the human telomerase protein catalytic subunit (hTERT) in the presence of recombinant human telomerase RNA (hTR) in a rabbit reticulocyte lysate (RRL) system. We analyzed telomerase activity and binding of hTR to hTERT in RRL by expressing different hTERT and hTR variants. hTRs containing nucleotide substitutions that are predicted to disrupt base pairing in the P3 helix of the pseudoknot weakly reconstituted human telomerase activity yet retained their ability to bind hTERT. Our results also identified two distinct regions of hTR that can independently bind hTERT in vitro. Furthermore, sequences or structures between nucleotides 208 and 330 of hTR (which include the conserved CR4-CR5 domain) were found to be important for hTERT-hTR interactions and for telomerase activity reconstitution. Human TERT carboxy-terminal amino acid deletions extending to motif E or the deletion of the first 280 amino acids abolished human telomerase activity without affecting the ability of hTERT to associate with hTR, suggesting that the RT and RNA binding functions of hTERT are separable. These results indicate that the reconstitution of human telomerase activity in vitro requires regions of hTERT that (i) are distinct from the conserved RT motifs and (ii) bind nucleotides distal to the hTR template sequence.
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Affiliation(s)
- F Bachand
- Department of Anatomy & Cell Biology, McGill University, Montréal, Québec, Canada H3A 2B2
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Hardy CD, Schultz CS, Collins K. Requirements for the dGTP-dependent repeat addition processivity of recombinant Tetrahymena telomerase. J Biol Chem 2001; 276:4863-71. [PMID: 11096070 DOI: 10.1074/jbc.m005158200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Telomerase is a reverse transcriptase responsible for adding simple sequence repeats to chromosome 3'-ends. The template for telomeric repeat synthesis is carried within the RNA component of the telomerase ribonucleoprotein complex. Telomerases can copy their internal templates with repeat addition processivity, reusing the same template multiple times in the extension of a single primer. For some telomerases, optimal repeat addition processivity requires high micromolar dGTP concentrations, a much higher dGTP concentration than required for processive nucleotide addition within a repeat. We have investigated the requirements for dGTP-dependent repeat addition processivity using recombinant Tetrahymena telomerase. By altering the template sequence, we show that repeat addition processivity retains the same dGTP-dependence even if dGTP is not the first nucleotide incorporated in the second repeat. Furthermore, no dNTP other than dGTP can stimulate repeat addition processivity, even if it is the first nucleotide incorporated in the second repeat. Using structural variants of dGTP, we demonstrate that the stimulation of repeat addition processivity is specific for dGTP base and sugar constituents but requires only a single phosphate group. However, all nucleotides that stimulate repeat addition processivity also inhibit or compete with dGTP incorporation into product DNA. By assaying telomerase complexes reconstituted with a variety of altered templates, we find that repeat addition processivity has an unanticipated template or product sequence specificity. Finally, we show that a novel, nascent product DNA binding site establishes dGTP-dependent repeat addition processivity.
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Affiliation(s)
- C D Hardy
- Division of Biochemistry and Molecular Biology, Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720-3204, USA
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Beattie TL, Zhou W, Robinson MO, Harrington L. Polymerization defects within human telomerase are distinct from telomerase RNA and TEP1 binding. Mol Biol Cell 2000; 11:3329-40. [PMID: 11029039 PMCID: PMC14995 DOI: 10.1091/mbc.11.10.3329] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The minimal, active core of human telomerase is postulated to contain two components, the telomerase RNA hTER and the telomerase reverse transcriptase hTERT. The reconstitution of human telomerase activity in vitro has facilitated the identification of sequences within the telomerase RNA and the RT motifs of hTERT that are essential for telomerase activity. However, the precise role of residues outside the RT domain of hTERT is unknown. Here we have delineated several regions within hTERT that are important for telomerase catalysis, primer use, and interaction with the telomerase RNA and the telomerase-associated protein TEP1. In particular, certain deletions of the amino and carboxy terminus of hTERT that retained an interaction with telomerase RNA and TEP1 were nonetheless completely inactive in vitro and in vivo. Furthermore, hTERT truncations lacking the amino terminus that were competent to bind the telomerase RNA were severely compromised for the ability to elongate telomeric and nontelomeric primers. These results suggest that the interaction of telomerase RNA with hTERT can be functionally uncoupled from polymerization, and that there are regions outside the RT domain of hTERT that are critical for telomerase activity and primer use. These results establish that the human telomerase RT possesses unique polymerization determinants that distinguish it from other RTs.
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Affiliation(s)
- T L Beattie
- Ontario Cancer Institute/Amgen Institute, Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 2C1 Canada
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Abstract
Telomerase is a cellular reverse transcriptase specialized for use of a template carried within the RNA component of the enzyme ribonucleoprotein complex. Substrates for telomerase are single-stranded oligonucleotides in vitro and chromosome ends in vivo. In vitro, a bound substrate is extended by an initial round of DNA synthesis on the internal RNA template and in some cases by multiple rounds of template copying before product dissociation. In vivo, de novo synthesis of one strand of a telomeric repeat sequence by telomerase balances the sequence loss resulting from incomplete replication of linear chromosome ends by RNA primer-requiring DNA polymerases. Telomerase biochemistry has been studied extensively by using partially purified cell extracts. Telomerase components are being identified and beginning to be produced in recombinant form. This review focuses on the enzyme mechanism of telomerases from ciliate species, thus far the most intensively studied systems.
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Affiliation(s)
- K Collins
- Department of Molecular and Cell Biology, University of California at Berkeley 94720-3204, USA.
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Ware TL, Wang H, Blackburn EH. Three telomerases with completely non-telomeric template replacements are catalytically active. EMBO J 2000; 19:3119-31. [PMID: 10856255 PMCID: PMC203363 DOI: 10.1093/emboj/19.12.3119] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Telomerase is a reverse transcriptase minimally composed of a reverse transcriptase protein subunit and an internal RNA component that contains the templating region. Point mutations of template RNA bases can cause loss of enzymatic activity, reduced processivity and misincorporation in vitro. Here we report the first complete replacement of the nine base TETRAHYMENA: thermophila telomerase templating region in vivo with non-telomeric sequences. Rather than ablating telomerase activity, three such replaced telomerases (U9, AUN and AU4) were effective in polymerization in vitro. In vivo, the AU4 and AUN genes caused telomere shortening. We demonstrated the fidelity of the AUN and U9 telomerases in vitro and utilized AUN telomerase to demonstrate that 5' end primer recognition by telomerase is independent of template base pairing. However, the mutant AUN template telomerase catalyzed an abnormal DNA cleavage reaction. For these U-only and AU- substituted templates, we conclude that base-specific interactions between the telomerase template and protein (or distant parts of the RNA) are not absolutely required for the minimal core telomerase functions of nucleotide addition and base discrimination.
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Affiliation(s)
- T L Ware
- Department of Biochemistry and Biophysics and Department of Microbiology and Immunology, Box 0414, University of California, San Francisco, CA 94143, USA
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Benjamin S, Baran N, Manor H. Interference footprinting analysis of telomerase elongation complexes. Mol Cell Biol 2000; 20:4224-37. [PMID: 10825187 PMCID: PMC85791 DOI: 10.1128/mcb.20.12.4224-4237.2000] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Telomerase is a reverse transcriptase that adds single-stranded telomeric repeats to the ends of linear eukaryotic chromosomes. It consists of an RNA molecule including a template sequence, a protein subunit containing reverse transcriptase motifs, and auxiliary proteins. We have carried out an interference footprinting analysis of the Tetrahymena telomerase elongation complexes. In this study, single-stranded oligonucleotide primers containing telomeric sequences were modified with base-specific chemical reagents and extended with the telomerase by a single (32)P-labeled dGMP or dTMP. Base modifications that interfered with the primer extension reactions were mapped by footprinting. Major functional interactions were detected between the telomerase and the six or seven 3'-terminal residues of the primers. These interactions occurred not only with the RNA template region, but also with another region in the enzyme ribonucleoprotein complex designated the telomerase DNA interacting surface (TDIS). This was indicated by footprints generated with dimethyl sulfate (that did not affect Watson-Crick hydrogen bonding) and by footprinting assays performed with mutant primers. In primers aligned at a distance of 2 nucleotides along the RNA template region, the footprints of the six or seven 3'-terminal residues were shifted by 2 nucleotides. This shift indicated that during the elongation reaction, TDIS moved in concert with the 3' ends of the primers relative to the template region. Weak interactions occurred between the telomerase and residues located upstream of the seventh nucleotide. These interactions were stronger in primers that were impaired in the ability to align with the template.
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Affiliation(s)
- S Benjamin
- Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
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47
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Abstract
The telomerase ribonucleoprotein has a phylogenetically divergent RNA subunit, which contains a short template for telomeric DNA synthesis. To understand how telomerase RNA participates in mechanistic aspects of telomere synthesis, we studied a conserved secondary structure adjacent to the template. Disruption of this structure caused DNA synthesis to proceed beyond the normal template boundary, resulting in altered telomere sequences, telomere shortening, and cellular growth defects. Compensatory mutations restored normal telomerase function. Thus, the RNA structure, rather than its sequence, specifies the template boundary. This study reveals a specific function for an RNA structure in the enzymatic action of telomerase.
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Affiliation(s)
- Y Tzfati
- Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, CA 94143-0414, USA
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48
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Abstract
Telomerase is a ribonucleoprotein enzyme that maintains telomere length by adding telomeric sequence repeats onto chromosome ends. The essential RNA component of telomerase provides the template for telomeric repeat synthesis. To determine the secondary structure of vertebrate telomerase RNA, 32 new telomerase RNA genes were cloned and sequenced from a variety of vertebrate species including 18 mammals, 2 birds, 1 reptile, 7 amphibians, and 4 fishes. Using phylogenetic comparative analysis, we propose a secondary structure that contains four structural domains conserved in all vertebrates. Ten helical regions of the RNA are universally conserved while other regions vary significantly in length and sequence between different classes of vertebrates. The proposed vertebrate telomerase RNA structure displays a strikingly similar topology to the previously determined ciliate telomerase RNA structure, implying an evolutionary conservation of the global architecture of telomerase RNA.
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Affiliation(s)
- J L Chen
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Affiliation(s)
- C Autexier
- Department of Anatomy and Cell Biology, McGill University, Montreal, Canada
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Tesmer VM, Ford LP, Holt SE, Frank BC, Yi X, Aisner DL, Ouellette M, Shay JW, Wright WE. Two inactive fragments of the integral RNA cooperate to assemble active telomerase with the human protein catalytic subunit (hTERT) in vitro. Mol Cell Biol 1999; 19:6207-16. [PMID: 10454567 PMCID: PMC84565 DOI: 10.1128/mcb.19.9.6207] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
We have mapped the 5' and 3' boundaries of the region of the human telomerase RNA (hTR) that is required to produce activity with the human protein catalytic subunit (hTERT) by using in vitro assembly systems derived from rabbit reticulocyte lysates and human cell extracts. The region spanning nucleotides +33 to +325 of the 451-base hTR is the minimal sequence required to produce levels of telomerase activity that are comparable with that made with full-length hTR. Our results suggest that the sequence approximately 270 bases downstream of the template is required for efficient assembly of active telomerase in vitro; this sequence encompasses a substantially larger portion of the 3' end of hTR than previously thought necessary. In addition, we identified two fragments of hTR (nucleotides +33 to +147 and +164 to +325) that cannot produce telomerase activity when combined separately with hTERT but can function together to assemble active telomerase. These results suggest that the minimal sequence of hTR can be divided into two sections, both of which are required for de novo assembly of active telomerase in vitro.
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Affiliation(s)
- V M Tesmer
- Department of Cell Biology and Neuroscience, The University of Texas Southwestern Medical Center, Dallas, Texas 75235-9039, USA
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