TERT is the catalytic protein subunit of telomerase, the ribonucleoprotein (RNP) reverse transcriptase that extends the single-stranded 3' ends of linear chromosomes with telomeric repeats. The 1117-residue protein comprises a telomerase-essential N-terminal (TEN) domain, an RNA-binding domain (TRBD), a reverse-transcriptase (RT) domain and a C-terminal extension (CTE); the TRBD, RT and CTE form a ring around the active-site cavity. Catalysis (EC 2.7.7.49) requires the integral RNA subunit TER, which supplies the internal template encoding the Tetrahymena 5'-TTGGGG-3' repeat, so the enzyme is an RNA-directed DNA polymerase whose template is part of the enzyme rather than a separate substrate. TERT itself determines how that internal template is used: single substitutions in the ciliate-specific N-terminal motif CP2 and in RT motifs 1, 2, A and D alter the 5' and 3' template boundaries, nucleotide- and repeat-addition processivity, and deoxy- versus ribonucleotide selectivity. The TEN domain binds the single-stranded telomeric DNA primer sequence-specifically and contacts RNA non-specifically, while the TRBD binds TER at the template-boundary element and loop 4. In Tetrahymena, TERT, TER and the La-family protein p65/TAP65 form the catalytic core of a larger holoenzyme that also contains the p50 hub, an RPA-paralogous TEB module (Teb1-Teb2-Teb3) and a CST-paralogous p75-p45-p19 module; these accessory modules, not TERT, supply high repeat-addition processivity and the physical bridge to the chromosome end. TERT acts in the nucleus at telomeric chromosome ends and is required for telomere length maintenance in vivo.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000333 telomerase catalytic core complex | IEA GO_REF:0000118 | ACCEPT | Summary: TERT is a constituent of the minimal catalytic core of telomerase, which in Tetrahymena is TERT plus the RNA subunit TER plus the La-family protein p65/TAP65. The GO definition of this complex, a catalytic reverse transcriptase subunit together with an RNA subunit that provides the template for telomeric DNA addition, describes TERT's situation exactly. Reason: The TreeGrafter/PAINT node placement is sound. TERT is by definition the reverse-transcriptase subunit of the telomerase catalytic core, and the Tetrahymena core has been resolved structurally as TERT-TER-p65. This term is more specific than the GO:0005697 holoenzyme rows and is retained as the core complex assignment. Supporting Evidence: PMID:23552895 Fitting with high-resolution structures reveals the organization of TERT, TER and p65 in the ribonucleoprotein (RNP) catalytic core. PMID:23552895 Three of these subunits are required for in vivo assembly of a catalytically active RNP: TERT, TER, and the La-family protein p65 |
| GO:0000723 telomere maintenance | IEA GO_REF:0000002 | TOO GENERAL | Summary: The claim is true, since TERT is required for telomere maintenance in Tetrahymena, but the specific mechanism term GO:0007004 telomere maintenance via telomerase is accepted elsewhere in this review, and GO:0000723 is its strict ancestor (QuickGO ancestor query). Reason: Not a false claim and not an over-annotation; simply uninformative once GO:0007004 telomere maintenance via telomerase is asserted, which entails it. The InterPro IPR003545 (Telomerase_RT) mapping is correct but stops one level short of the mechanism the family defines. Supporting Evidence: PMID:19941821 Each of seven telomerase proteins is required for telomere maintenance and copurifies active RNP. |
| GO:0000781 chromosome, telomeric region | IEA GO_REF:0000044 | ACCEPT | Summary: Telomerase acts at chromosome ends, and the holoenzyme is physically bridged to telomeres by its accessory subunits; TERT travels with it as the catalytic subunit. UniProt records Chromosome, telomere for this entry, citing PubMed:16462747 alongside its rule-based assertion. Reason: Correct site of action. The Tetrahymena-specific support is indirect, resting on TEN-domain binding of a single-stranded telomeric primer plus in vivo telomere elongation rather than on a microscopy or ChIP localisation in the cached literature, but the claim is not in doubt and no more precise component term is warranted. Note that the recruitment machinery itself (p50, Teb1/TEB) belongs to other subunits, so this row is kept as a location for TERT and not read as a recruitment function. Supporting Evidence: PMID:23552895 reveals the organization of holoenzyme subunits that confer processivity and bridge telomerase to telomeres PMID:16462747 These residues are crucial for telomerase catalytic activity, and several of them are required for sequence-specific binding of a single-stranded telomeric DNA primer. |
| GO:0003677 DNA binding | IEA GO_REF:0000002 | TOO GENERAL | Summary: TERT does bind DNA, specifically the single-stranded telomeric primer via the TEN domain, but GO:0003677 is a strict ancestor of the telomeric DNA-binding term carried elsewhere in this review (QuickGO ancestor query), so it adds nothing. Reason: True but uninformative. GO:0043047 single-stranded telomeric DNA binding, proposed as the replacement for the GO:0042162 rows, entails GO:0003677. This judges the term, not the InterPro mapping, which is correct as far as it goes. Supporting Evidence: PMID:16462747 These residues are crucial for telomerase catalytic activity, and several of them are required for sequence-specific binding of a single-stranded telomeric DNA primer. |
| GO:0003720 telomerase activity | IDA PMID:10944124 Template definition by Tetrahymena telomerase reverse transc... | ACCEPT | Summary: The defining molecular function of TERT. This study reconstituted recombinant Tetrahymena telomerase from TERT and TER and measured primer extension directly, showing that 54 single substitutions in TERT alter the level and the qualitative features of repeat synthesis. Reason: Core function, established in the organism being annotated. GO:0003720 is the right level of specificity, since its definition requires catalysis using an internal RNA template that encodes the telomeric repeat sequence, which is precisely what distinguishes telomerase from the generic DNA-polymerase and RNA-directed-DNA-polymerase ancestors. The activity is strictly a property of the TERT-TER RNP, but TERT carries the RT active site and determines template use, which is why GOA annotates the protein subunit with it. Supporting Evidence: PMID:10944124 Only two telomerase components are known to be essential for properly templated telomerase activity assayed on oligonucleotide substrates: the telomerase RNA and the telomerase reverse transcriptase (TERT) protein. PMID:10944124 Our results indicate that TERT contributes directly to RNA template definition and the characteristics of template use. |
| GO:0003720 telomerase activity | IDA PMID:15696174 A telomerase holoenzyme protein enhances telomerase RNA asse... | ACCEPT | Summary: This study assembled TERT with TER in rabbit reticulocyte lysate and assayed primer extension, confirming that the TERT-TER pair alone constitutes an active enzyme. Reason: Reinforces the same core claim as the other GO:0003720 rows with an independent reconstitution. The paper is primarily about p65, but it explicitly measures TERT-TER primer-extension activity, so the annotation is well placed. Supporting Evidence: PMID:15696174 The telomerase reverse transcriptase (TERT) and telomerase RNA (TER) alone can assemble into active enzyme in a heterologous cell extract PMID:15696174 Coassembly of p65 did not affect the primer-extension activity of T. thermophila TERT reconstituted with TER in RRL |
| GO:0003720 telomerase activity | IDA PMID:16462747 Crystal structure of the essential N-terminal domain of telo... | ACCEPT | Summary: The TEN-domain crystal structure paper mutated conserved surface residues and scored telomerase catalytic activity, showing those residues are required for it. Reason: Correct, and consistent with the other GO:0003720 rows. The cached record is abstract-only, but the abstract itself states that the mutated residues are crucial for telomerase catalytic activity, so the curator's IDA is directly corroborated by the accessible text. Supporting Evidence: PMID:16462747 These residues are crucial for telomerase catalytic activity |
| GO:0003720 telomerase activity | IDA PMID:20713447 Tetrahymena telomerase protein p65 induces conformational ch... | ACCEPT | Summary: This study used purified p65 together with TERT and TER variants and measured telomerase activity, distinguishing TERT assembly mutants, which p65 rescued, from TERT activity mutants, which it did not. Reason: Correct. The cached record is abstract-only, but the abstract states that TERT activity mutants were assayed and were not rescued by p65, which presupposes direct measurement of TERT-dependent telomerase activity. Consistent with the other GO:0003720 rows. Supporting Evidence: PMID:20713447 Several TER mutants exhibited telomerase activity only in the presence of p65 |
| GO:0003720 telomerase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic assertion of the same core function from the Telomerase_RT InterPro signature and an ARBA rule. Reason: The electronic mapping lands on exactly the term that four experimental rows in this review also support; it is right, and at the right level of specificity. Rows sharing a term reinforce each other, so this is accepted rather than treated as a duplicate. Supporting Evidence: PMID:10944124 The ribonucleoprotein enzyme telomerase extends chromosome ends by copying a specific template sequence within its integral RNA component. |
| GO:0003964 RNA-directed DNA polymerase activity | IEA GO_REF:0000120 | TOO GENERAL | Summary: True, since telomerase is an RNA-templated DNA polymerase and UniProt assigns EC 2.7.7.49 to this entry with four experimental references, but GO:0003964 is a strict ancestor of GO:0003720 telomerase activity (QuickGO ancestor query), which is accepted elsewhere in this review. Reason: The EC 2.7.7.49 mapping is correct and the claim is not in doubt; it is simply entailed by the accepted telomerase-activity term, which additionally captures that the RNA template is internal to the enzyme. Judges the term, not the mapping. Supporting Evidence: PMID:10944124 An active recombinant telomerase RNP is minimally composed of this RNA and the telomerase reverse transcriptase (TERT) protein |
| GO:0005634 nucleus | IEA GO_REF:0000044 | ACCEPT | Summary: TERT acts on nuclear chromosome ends, and UniProt records Nucleus for this entry. Tetrahymena has two nuclei (macronucleus and micronucleus, GO:0031039 and GO:0031040), and the cached literature does not resolve which compartment was assayed. Reason: Correct and, given the available evidence, as precise as is warranted. The generic nucleus term is kept rather than modified to macronucleus, because no cached Tetrahymena source distinguishes the two nuclei for TERT. Refining this is raised as a suggested question instead of being asserted here. Supporting Evidence: file:TETTS/TERT/TERT-uniprot.txt SUBCELLULAR LOCATION: Nucleus |
| GO:0005697 telomerase holoenzyme complex | IDA PMID:15696174 A telomerase holoenzyme protein enhances telomerase RNA asse... | ACCEPT | Summary: TERT was shown to co-assemble with TER and the holoenzyme protein p65 into a ternary complex, placing it in the Tetrahymena telomerase holoenzyme. Reason: Directly demonstrated membership. The holoenzyme term remains informative alongside the narrower catalytic-core term because the Tetrahymena holoenzyme is a distinct, biologically functional nine-subunit entity whose composition was established in these very papers. Supporting Evidence: PMID:15696174 These findings demonstrate that in the presence of TER, p65 and TERT associate to form a ternary complex. |
| GO:0005697 telomerase holoenzyme complex | IDA PMID:19941821 An RPA-related sequence-specific DNA-binding subunit of telo... | ACCEPT | Summary: Affinity purification from Tetrahymena defined a seven-protein holoenzyme built around the p65-TER-TERT catalytic core, with the p75-p45-p19 subcomplex and the peripheral p82 and p50 subunits. Reason: Direct experimental identification of TERT within the holoenzyme in the organism being annotated. This row also establishes the division of labour used throughout this review, namely that processivity and DNA handling come from Teb1/p82 and p50 rather than from TERT. Supporting Evidence: PMID:19941821 The catalytic core (p65-TER-TERT) is assembled with a three-protein subcomplex (p75-p45-p19) and two peripheral subunits (p82 and p50). PMID:19941821 Each of seven telomerase proteins is required for telomere maintenance and copurifies active RNP. |
| GO:0005697 telomerase holoenzyme complex | IDA PMID:20713447 Tetrahymena telomerase protein p65 induces conformational ch... | ACCEPT | Summary: TERT was reconstituted with TER and the holoenzyme protein p65, which stabilises TER and TERT within the assembled RNP. Reason: Consistent with the other GO:0005697 rows. The cached record is abstract-only, but the abstract describes TERT within an assembled RNP containing p65 and TER, which is the claim being made. Supporting Evidence: PMID:20713447 p65 acts as a molecular buttress within the assembled RNP, mutually stabilizing TER and TERT in catalytically active conformations |
| GO:0005697 telomerase holoenzyme complex | IDA PMID:23552895 The architecture of Tetrahymena telomerase holoenzyme. | ACCEPT | Summary: Electron microscopy of the affinity-purified Tetrahymena holoenzyme localised six of seven proteins plus TER, with TERT occupying the centre of the particle and p50 acting as a hub to the p75-p19-p45 subcomplex and Teb1. Reason: The strongest structural demonstration of TERT's position within the holoenzyme. Directly supports part_of membership. Supporting Evidence: PMID:23552895 Fitting with high-resolution structures reveals the organization of TERT, TER and p65 in the ribonucleoprotein (RNP) catalytic core. PMID:23552895 Affinity purification, mass spectrometry, and subunit tagging assays have established 8 telomerase-specific, reciprocally co-purifying subunits of Tetrahymena telomerase holoenzyme, each essential for telomere length maintenance |
| GO:0005697 telomerase holoenzyme complex | IDA PMID:26472759 Structure of Tetrahymena telomerase reveals previously unkno... | ACCEPT | Summary: The cryo-EM structure of Tetrahymena telomerase resolved TERT within the holoenzyme and identified two further subunits, defining the RPA-paralogous TEB module and the CST-paralogous p75-p45-p19 module. Reason: Direct structural evidence for TERT as a holoenzyme subunit, and the reference that fixes the Tetrahymena-specific composition, namely TEB and CST paralogs rather than shelterin. Consistent with the other GO:0005697 rows. Supporting Evidence: PMID:26472759 extensive subunit interactions of the TERT essential N-terminal domain, p50, and TEB PMID:26472759 The p75-p45-p19 subcomplex is identified as another RPA-related complex, CST (CTC1-STN1-TEN1). |
| GO:0007004 telomere maintenance via telomerase | IDA PMID:15696174 A telomerase holoenzyme protein enhances telomerase RNA asse... | ACCEPT | Summary: TERT is the catalytic subunit that synthesises the telomeric repeats by which telomere length is maintained; this paper reconstituted the TERT-TER enzyme and the physiological p65-dependent biogenesis pathway that produces it in vivo. Reason: This is the process TERT itself executes, since it catalyses the repeat-addition step, so the participation test is satisfied directly rather than by necessity evidence. The mechanism-specific term is the right level; its ancestor GO:0000723 is marked TOO_GENERAL elsewhere in this review. Supporting Evidence: PMID:15696174 Telomerase maintains the simple sequence repeats at chromosome ends, protecting cells from genomic rearrangement, proliferative senescence and death. PMID:15696174 The telomerase reverse transcriptase (TERT) and telomerase RNA (TER) alone can assemble into active enzyme in a heterologous cell extract |
| GO:0007004 telomere maintenance via telomerase | IEA GO_REF:0000118 | ACCEPT | Summary: TreeGrafter propagation of the telomerase-mediated telomere maintenance process from the TERT ancestral node, reinforcing the IDA row to the same term. Reason: The PAINT node placement is sound. Telomerase-mediated telomere maintenance is the ancestral function of the TERT family and Tetrahymena TERT sits squarely inside the clade, with its own experimental annotation to the same term. The propagated row says something the IDA row does not, namely that the function is inherited rather than lineage-specific. Supporting Evidence: PMID:19941821 Each of seven telomerase proteins is required for telomere maintenance and copurifies active RNP. |
| GO:0034061 DNA polymerase activity | EXP PMID:10944124 Template definition by Tetrahymena telomerase reverse transc... | TOO GENERAL | Summary: True, since TERT catalyses template-directed addition of dNTPs to a DNA 3' end, but GO:0034061 is a strict ancestor of both GO:0003964 and GO:0003720 (QuickGO ancestor query), and GO:0003720 telomerase activity is accepted elsewhere in this review from this same reference. Reason: Uninformative rather than wrong, and the experimental evidence behind it is not in question. The same paper's data support the specific telomerase-activity term, which entails this one and additionally encodes the internal-template distinction. This is a judgement about the term, not about the EXP evidence. Supporting Evidence: PMID:10944124 We conclude that the major qualitative change in activity of the Class 5 enzyme derives from a loss of dNTP/rNTP selectivity. |
| GO:0034061 DNA polymerase activity | EXP PMID:15696174 A telomerase holoenzyme protein enhances telomerase RNA asse... | TOO GENERAL | Summary: As for the other GO:0034061 rows, correct but a strict ancestor of the accepted GO:0003720 telomerase activity, which this same reference also supports. Reason: Entailed by the specific term accepted elsewhere in this review. Kept consistent with the other four DNA-polymerase-activity rows; never a reason to doubt the primer extension measured here. Supporting Evidence: PMID:15696174 Coassembly of p65 did not affect the primer-extension activity of T. thermophila TERT reconstituted with TER in RRL |
| GO:0034061 DNA polymerase activity | EXP PMID:16462747 Crystal structure of the essential N-terminal domain of telo... | TOO GENERAL | Summary: As for the other GO:0034061 rows, true and supported by this paper's mutagenesis of catalytically required TEN-domain residues, but entailed by the accepted GO:0003720. Reason: A strict ancestor of telomerase activity, which this same reference supports and which is accepted in this review. Consistent with the other DNA-polymerase-activity rows. Supporting Evidence: PMID:16462747 These residues are crucial for telomerase catalytic activity |
| GO:0034061 DNA polymerase activity | EXP PMID:20713447 Tetrahymena telomerase protein p65 induces conformational ch... | TOO GENERAL | Summary: As for the other GO:0034061 rows, true but entailed by the accepted GO:0003720 telomerase activity, which this same reference also supports. Reason: A strict ancestor of the specific term accepted in this review. The abstract-only cache is sufficient to confirm that TERT-dependent telomerase activity was measured; the issue is the term's level, not the evidence. Supporting Evidence: PMID:20713447 Several TER mutants exhibited telomerase activity only in the presence of p65 |
| GO:0034061 DNA polymerase activity | IEA GO_REF:0000116 | TOO GENERAL | Summary: Rhea mapping of the generic DNA-polymerase reaction (RHEA:22508) recorded in UniProt for this entry together with EC 2.7.7.49. Reason: The Rhea reaction is the correct chemistry, but GO:0034061 is a strict ancestor of the accepted GO:0003720 telomerase activity, whose GO definition is the same reaction qualified by the internal RNA template. Entailed, therefore uninformative; consistent with the four EXP rows to the same term. Supporting Evidence: PMID:10944124 The ribonucleoprotein enzyme telomerase extends chromosome ends by copying a specific template sequence within its integral RNA component. |
| GO:0042162 telomeric repeat DNA binding | IDA PMID:16462747 Crystal structure of the essential N-terminal domain of telo... | MODIFY | Summary: The TEN crystal structure paper showed that conserved surface residues of the Tetrahymena TERT N-terminal domain are required for sequence-specific binding of a single-stranded telomeric DNA primer. What TERT engages is the single-stranded 3' telomeric overhang, not duplex telomeric repeat DNA. Reason: The essence is right but the term is less specific than the evidence supports. The cited paper states explicitly that the binding is to a single-stranded telomeric DNA primer, and GO:0043047 single-stranded telomeric DNA binding is an is_a descendant of GO:0042162 (QuickGO) that also falls under GO:0003697 single-stranded DNA binding. This is the substrate telomerase actually extends, so the narrower term is both true and more informative. Proposed replacements: single-stranded telomeric DNA binding Supporting Evidence: PMID:16462747 These residues are crucial for telomerase catalytic activity, and several of them are required for sequence-specific binding of a single-stranded telomeric DNA primer. PMID:26472759 Telomerase helps maintain telomeres by processive synthesis of telomere repeat DNA at their 3'-ends, using an integral telomerase RNA (TER) and telomerase reverse transcriptase (TERT). |
| GO:0042162 telomeric repeat DNA binding | IEA GO_REF:0000118 | MODIFY | Summary: TreeGrafter propagation of telomeric repeat DNA binding from the TERT ancestral node. Correct for the family, but the Tetrahymena evidence identifies the ligand more precisely as the single-stranded telomeric primer. Reason: Refined for the same reason as the IDA row to this term, and kept consistent with it. This is not a challenge to the PAINT node placement, since telomeric DNA binding is ancestral to TERT; it is only a refinement to the single-stranded descendant term that the target-specific structural evidence supports. Proposed replacements: single-stranded telomeric DNA binding Supporting Evidence: PMID:16462747 These residues are crucial for telomerase catalytic activity, and several of them are required for sequence-specific binding of a single-stranded telomeric DNA primer. |
| GO:0070034 telomerase RNA binding | IDA PMID:16462747 Crystal structure of the essential N-terminal domain of telo... | ACCEPT | Summary: TERT binds its integral RNA subunit TER. The TEN domain's positively charged C terminus binds RNA non-sequence-specifically, while the TRBD binds TER at the template-boundary element and loop 4; the TERT-TER contacts were later resolved structurally. Reason: Core molecular function and the right level of specificity, since TER binding is what converts a reverse-transcriptase fold into telomerase. Supported directly by the cited paper's abstract and corroborated by the holoenzyme structures. Supporting Evidence: PMID:16462747 The positively charged C terminus, which becomes ordered upon interaction with other macromolecules, is involved in binding RNA in a non-sequence-specific manner. PMID:26472759 This study reveals the paths of TER in the TERT-TER-p65 catalytic core and single-stranded DNA exit |
| GO:0070034 telomerase RNA binding | IEA GO_REF:0000118 | ACCEPT | Summary: TreeGrafter propagation of telomerase RNA binding from the TERT ancestral node, reinforcing the IDA row to the same term. Reason: The node placement is sound, since every TERT binds its cognate TER, and the Tetrahymena protein has its own experimental evidence for it, so the propagation is both correct and grounded. Accepted at the same level as the IDA row. Supporting Evidence: PMID:23552895 The TERT TRBD, RT domain, and C-terminal extension (CTE) form a ring that encircles an active site cavity |
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Download this section (compressed HTML)Q: Does Tetrahymena TERT localise to the macronucleus, the micronucleus, or both? The generic GO:0005634 nucleus term is retained in this review because no cached source distinguishes the two nuclei, yet GO:0031039 macronucleus and GO:0031040 micronucleus exist and the two nuclei differ radically in telomere number and replication mode.
Q: Should GO offer a way to record that telomerase activity is a property of the TERT-TER ribonucleoprotein rather than of the protein alone? TERT carries the active site but cannot catalyse anything without its integral RNA subunit, and the existing enables/contributes_to distinction does not capture a protein-RNA holoenzyme cleanly.
Q: Is the sequence-specific single-stranded telomeric DNA binding of the TERT TEN domain an anchor site distinct from the primer-template duplex in the active site, and is it retained across non-ciliate TERTs, or is it a ciliate elaboration like the CP2 motif?
Q: Which Tetrahymena holoenzyme subunit should carry a processivity-related GO term? The cached literature assigns high repeat-addition processivity to Teb1/p82 and the p50 hub rather than to TERT, so a processivity annotation on TERT would misplace the function.
Experiment: Tag endogenous TERT and image it relative to macronuclear and micronuclear markers through the vegetative cell cycle and through conjugation, when new macronuclear telomeres are added de novo.
Hypothesis: TERT is predominantly macronuclear in vegetative cells and is recruited to the developing macronucleus during conjugation, which would justify refining GO:0005634 nucleus to GO:0031039 macronucleus.
Experiment: Separate the TEN-domain primer-anchor site from the active site by combining the TEN surface-groove substitutions that abolish sequence-specific single-stranded telomeric DNA binding with primers whose 3' permutation forces different active-site registers, measuring binding by fluorescence anisotropy and activity by direct primer extension.
Hypothesis: The TEN groove is a separate single-stranded telomeric DNA anchor whose loss reduces primer affinity and repeat-addition processivity without altering the chemistry of nucleotide addition.
Experiment: Reconstitute the full nine-subunit holoenzyme from recombinant parts and systematically omit the p50, TEB and CST modules while measuring repeat-addition processivity and telomeric-DNA binding of TERT-TER alone versus each partial assembly.
Hypothesis: Processivity and telomere engagement are contributed by p50, TEB and CST and not by TERT, so these functions should be annotated on those subunits rather than on TERT.
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