Cryo–electron microscopy structure of the budding yeast telomerase holoenzyme.
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| Title: | Cryo–electron microscopy structure of the budding yeast telomerase holoenzyme. |
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| Authors: | Hu, Hongmiao (AUTHOR), Neumann, Hannah (AUTHOR), Teplitz, Gabriela M. (AUTHOR), Franco-Echevarría, Elsa (AUTHOR), Chartrand, Pascal (AUTHOR), Wellinger, Raymund J. (AUTHOR), Nguyen, Thi Hoang Duong (AUTHOR) |
| Source: | Science. 3/26/2026, Vol. 391 Issue 6792, p1-15. 15p. |
| Subjects: | Telomerase, Electron cryomicroscopy, Saccharomyces cerevisiae, Zinc-finger proteins, Telomerase reverse transcriptase, Phylogeny, Nucleoproteins |
| Abstract: | Telomerase is a reverse transcriptase that synthesizes telomeric repeats at chromosome ends, safeguarding genome integrity. We present the cryo–electron microscopy structure of the budding yeast telomerase, which exhibits substantial divergence from its ciliate and vertebrate counterparts. The structure reveals a stable core formed by telomerase RNA TLC1; the three ever shorter telomere (Est) proteins, Est1, Est2 and Est3; and the Pop1/Pop6/Pop7 complex (Pop1/6/7). TLC1, Est3, and Pop1/6/7 serve critical roles in complex assembly. We identified a zinc finger (ZnF) motif in the telomerase reverse transcriptase (TERT) subunit Est2 that is crucial for telomerase function. Structure prediction suggests the presence of ZnFs in TERT from diverse species. These findings offer insights into the functional organization of yeast telomerase and underscore the evolutionary diversity of telomerase holoenzymes. Editor's summary: Most eukaryotes use the telomerase ribonucleoprotein to maintain chromosome ends. Although its catalytic function is conserved, telomerase exhibits remarkable evolutionary divergence, with highly variable RNA components and distinct sets of associated proteins. Hu et al. present the cryo–electron microscopy structure of budding yeast telomerase, revealing its molecular architecture and clarifying the functional roles of its components. Structural predictions indicate that divergence in the conserved telomerase reverse transcriptase may accommodate the variable RNA, underscoring the evolutionary diversity of telomerases across eukaryotes. —Di Jiang INTRODUCTION: Telomerase adds telomeric DNA repeats to chromosome ends, preserving genome integrity. Its catalytic core comprises telomerase reverse transcriptase (TERT) that synthesizes DNA using an RNA template within telomerase RNA (TR). Across eukaryotes, TRs vary greatly in sizes and predicted secondary structures, resulting in a substantial diversity in holoenzyme composition. Studies in ciliates, yeasts, and humans have been pivotal in establishing our understanding of telomerase biology. Cryo–electron microscopy (cryo-EM) structures of human and Tetrahymena telomerases have provided insights into their architecture, mechanism, and regulation. Structures of active yeast telomerase remain lacking. Yeast TRs are unusually large and predicted to form flexible scaffolds for protein subunits. How yeast telomerase achieves its conserved function despite its divergent composition and expansive RNA is unknown. RATIONALE: Saccharomyces cerevisiae telomerase contains an RNA component, TLC1, and 15 protein subunits, including the three ever shorter telomere (Est) proteins, Est1, Est2 (budding yeast TERT), and Est3; the yKu70/Ku80 (yKu) heterodimer; the Sm heptamer (Sm7); and the Pop1/Pop6/Pop7 (Pop1/6/7) heterotrimer. The structural basis for subunit organization and functions remains elusive. We sought to elucidate the molecular architecture of S. cerevisiae telomerase and define key interactions underlying telomerase function. RESULTS: We reconstituted telomerase by coexpressing Est1, Est2, Est3, and TLC1 in yeast and purified it for cryo-EM. The resulting structure shows that several distant regions of TLC1 converge to form a compact core with the three Est proteins and Pop1/6/7 complex, whereas the yKu and Sm7 complexes are flexibly tethered through long RNA linkers. The oligosaccharide/oligonucleotide-binding (OB) fold protein Est3 is a key protein-protein interaction hub that stabilizes the holoenzyme. Disrupting Est3 interactions with Est2 and Pop1 caused telomere shortening and senescence in vivo, demonstrating their functional importance. Structural analysis confirmed that Est3 is a homolog of human TPP1, a component of the telomere-associated shelterin complex, which transiently recruits telomerase to telomeres in humans. The Pop1/6/7 complex is shared with ribonuclease P and MRP, which are involved in RNA processing. In our structure, the Pop1/6/7 complex facilitates the association of the three Est proteins, rationalizing its role in telomerase assembly. We identified a Pop1 loop that is required for telomere maintenance but is dispensable for RNA processing. The Pop1/6/7 complex is, therefore, a bona fide telomerase component with a telomere-specific role. Comparison with the human and Tetrahymena telomerases reveals structural divergence among holoenzymes yet conservation of the catalytic core. Within this core, we discovered a Zinc finger motif (ZnF) in Est2 that is conserved among Saccharomycetales and Saccharomycodales. This ZnF is essential for telomerase activity in vitro and in vivo, likely through stabilization of the RNA template during catalysis. AlphaFold3 predicts diverse insertions of ZnF motifs in TERTs from multiple lineages, suggesting evolutionary remodeling of TERT to accommodate structurally distinct TRs. CONCLUSION: Our work defines the architectural principles governing assembly of a telomerase built on a large and flexible RNA scaffold. These principles are likely shared with other yeast telomerases and long noncoding ribonucleoproteins. We further uncovered species-specific innovations in subunit organization and the evolutionary adaptations that preserve catalytic function across highly divergent holoenzymes. Structure of the S. cerevisiae telomerase holoenzyme.: The structure of yeast telomerase provides insights into its molecular architecture and the function of holoenzyme subunits. Together with reported structures of the human and Tetrahymena telomerases, it reveals divergent architectural principles among eukaryotic telomerases while preserving a conserved function at chromosome ends. RPA, replication protein A; CST, Ctc1-Stn1-Ten1. [Figure created with BioRender.com] [ABSTRACT FROM AUTHOR] |
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| Database: | Psychology and Behavioral Sciences Collection |
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| Abstract: | Telomerase is a reverse transcriptase that synthesizes telomeric repeats at chromosome ends, safeguarding genome integrity. We present the cryo–electron microscopy structure of the budding yeast telomerase, which exhibits substantial divergence from its ciliate and vertebrate counterparts. The structure reveals a stable core formed by telomerase RNA TLC1; the three ever shorter telomere (Est) proteins, Est1, Est2 and Est3; and the Pop1/Pop6/Pop7 complex (Pop1/6/7). TLC1, Est3, and Pop1/6/7 serve critical roles in complex assembly. We identified a zinc finger (ZnF) motif in the telomerase reverse transcriptase (TERT) subunit Est2 that is crucial for telomerase function. Structure prediction suggests the presence of ZnFs in TERT from diverse species. These findings offer insights into the functional organization of yeast telomerase and underscore the evolutionary diversity of telomerase holoenzymes. Editor's summary: Most eukaryotes use the telomerase ribonucleoprotein to maintain chromosome ends. Although its catalytic function is conserved, telomerase exhibits remarkable evolutionary divergence, with highly variable RNA components and distinct sets of associated proteins. Hu et al. present the cryo–electron microscopy structure of budding yeast telomerase, revealing its molecular architecture and clarifying the functional roles of its components. Structural predictions indicate that divergence in the conserved telomerase reverse transcriptase may accommodate the variable RNA, underscoring the evolutionary diversity of telomerases across eukaryotes. —Di Jiang INTRODUCTION: Telomerase adds telomeric DNA repeats to chromosome ends, preserving genome integrity. Its catalytic core comprises telomerase reverse transcriptase (TERT) that synthesizes DNA using an RNA template within telomerase RNA (TR). Across eukaryotes, TRs vary greatly in sizes and predicted secondary structures, resulting in a substantial diversity in holoenzyme composition. Studies in ciliates, yeasts, and humans have been pivotal in establishing our understanding of telomerase biology. Cryo–electron microscopy (cryo-EM) structures of human and Tetrahymena telomerases have provided insights into their architecture, mechanism, and regulation. Structures of active yeast telomerase remain lacking. Yeast TRs are unusually large and predicted to form flexible scaffolds for protein subunits. How yeast telomerase achieves its conserved function despite its divergent composition and expansive RNA is unknown. RATIONALE: Saccharomyces cerevisiae telomerase contains an RNA component, TLC1, and 15 protein subunits, including the three ever shorter telomere (Est) proteins, Est1, Est2 (budding yeast TERT), and Est3; the yKu70/Ku80 (yKu) heterodimer; the Sm heptamer (Sm7); and the Pop1/Pop6/Pop7 (Pop1/6/7) heterotrimer. The structural basis for subunit organization and functions remains elusive. We sought to elucidate the molecular architecture of S. cerevisiae telomerase and define key interactions underlying telomerase function. RESULTS: We reconstituted telomerase by coexpressing Est1, Est2, Est3, and TLC1 in yeast and purified it for cryo-EM. The resulting structure shows that several distant regions of TLC1 converge to form a compact core with the three Est proteins and Pop1/6/7 complex, whereas the yKu and Sm7 complexes are flexibly tethered through long RNA linkers. The oligosaccharide/oligonucleotide-binding (OB) fold protein Est3 is a key protein-protein interaction hub that stabilizes the holoenzyme. Disrupting Est3 interactions with Est2 and Pop1 caused telomere shortening and senescence in vivo, demonstrating their functional importance. Structural analysis confirmed that Est3 is a homolog of human TPP1, a component of the telomere-associated shelterin complex, which transiently recruits telomerase to telomeres in humans. The Pop1/6/7 complex is shared with ribonuclease P and MRP, which are involved in RNA processing. In our structure, the Pop1/6/7 complex facilitates the association of the three Est proteins, rationalizing its role in telomerase assembly. We identified a Pop1 loop that is required for telomere maintenance but is dispensable for RNA processing. The Pop1/6/7 complex is, therefore, a bona fide telomerase component with a telomere-specific role. Comparison with the human and Tetrahymena telomerases reveals structural divergence among holoenzymes yet conservation of the catalytic core. Within this core, we discovered a Zinc finger motif (ZnF) in Est2 that is conserved among Saccharomycetales and Saccharomycodales. This ZnF is essential for telomerase activity in vitro and in vivo, likely through stabilization of the RNA template during catalysis. AlphaFold3 predicts diverse insertions of ZnF motifs in TERTs from multiple lineages, suggesting evolutionary remodeling of TERT to accommodate structurally distinct TRs. CONCLUSION: Our work defines the architectural principles governing assembly of a telomerase built on a large and flexible RNA scaffold. These principles are likely shared with other yeast telomerases and long noncoding ribonucleoproteins. We further uncovered species-specific innovations in subunit organization and the evolutionary adaptations that preserve catalytic function across highly divergent holoenzymes. Structure of the S. cerevisiae telomerase holoenzyme.: The structure of yeast telomerase provides insights into its molecular architecture and the function of holoenzyme subunits. Together with reported structures of the human and Tetrahymena telomerases, it reveals divergent architectural principles among eukaryotic telomerases while preserving a conserved function at chromosome ends. RPA, replication protein A; CST, Ctc1-Stn1-Ten1. [Figure created with BioRender.com] [ABSTRACT FROM AUTHOR] |
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| ISSN: | 00368075 |
| DOI: | 10.1126/science.adz5344 |
