Telomerase as a DNA-Dependent DNA Polymerase

Legassie, Jason D.; Jarstfer, Michael B.

doi:10.1021/bi050628s

Cited by 11 publications

(8 citation statements)

References 55 publications

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“…14c Although there is some evidence that TERT can utilize alternative templates, this alternative activity appears much less efficient than its canonical acticty. 19 Like all reverse transcriptases, telomerase catalyzes processive nucleotide addition to its primer. Uniquely, telomerase also efficiently conducts repeat addition processivity to generate long copies of its repetitive DNA product.…”

Section: Introductionmentioning

confidence: 99%

New Models of Tetrahymena Telomerase RNA from Experimentally Derived Constraints and Modeling

et al. 2012

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The telomerase ribonucleoprotein complex ensures complete replication of eukaryotic chromosomes. Telomerase RNA, TER, provides the template for replicating the G-rich strand of telomeric DNA, provides an anchor site for telomerase-associated proteins, and participates in catalysis through several incompletely characterized mechanisms. A major impediment towards understanding its non-templating roles is the absence of high content structural information for TER within the telomerase complex. Here, we used selective 2′-hydroxyl acylation analyzed by primer extension (SHAPE) to examine the structure of Tetrahymena TER free in solution and bound to tTERT in the minimal telomerase RNP. We discovered a striking difference in the two conformations and established direct evidence for base pair triples in the tTER pseudoknot. We then used SHAPE data, previously published FRET data, and biochemical inference to model the structure of tTER using discrete molecular dynamics simulations. The resulting tTER structure was docked with a homology model of tTERT to characterize the conformational changes of tTER that attend binding to tTERT. Free in solution, tTER appears to contain four pairing regions: stems I, II, and IV, which are present in the commonly accepted structure, and stem III, a large paired region that encompasses the template and pseudoknot domains. Our interpretation of the data and subsequent modeling affords a molecular model for telomerase assemblage in which a large stem III of tTER unwinds to allow proper association of the template with the tTERT active site and formation of the pseudoknot. Additionally, analysis of our SHAPE data and previous enzymatic footpinting allows us to propose a model for stem-loop IV function in which tTERT is activated by binding stem IV in the major grove of the helix-capping loop.

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Section: Introductionmentioning

confidence: 99%

New Models of Tetrahymena Telomerase RNA from Experimentally Derived Constraints and Modeling

et al. 2012

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“…Telomerase synthesizes telomeric repeats at the ends of chromosomes using a catalytic protein subunit known as telomerase reverse transcriptase (TERT) and an integral RNA subunit as the template (Legassie et al 2005). Although other proteins are involved in the function of the telomerase complex, these two essential components are conserved among all eukaryotes (Weinrich et al 1997).…”

Section: Introductionmentioning

confidence: 99%

Characterization of telomeres and telomerase expression in Xiphophorus

Downs¹,

Shen²,

Pasquali³

et al. 2012

Comparative Biochemistry and Physiology Part C: Toxicology &

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Research investigating telomere lengths and telomerase expression in vertebrates has progressively become important due to the association of these two biological endpoints with cellular aging and cancer in humans. Studies that rely upon the traditional use of laboratory mice have been faced with limitations largely due to inbred mice possessing large telomeres and ubiquitous expression of telomerase. Recently, a number of small fish species have been shown to provide potentially informative models for examining the role of telomeres and telomerase within intact vertebrate animals. Xiphophorus fishes represent a new world live-bearing genus that has not previously been assessed for telomere length or telomerase expression. To add to the knowledge base of telomere and telomerase biology in vertebrates we assessed telomere length and telomerase expression among several species of Xiphophorus. The telomere lengths in several organs (gill, brain, eyes, testis, ovary and liver) in three species (X. hellerii, X. maculatus, X. couchianus) and also in F1 interspecies hybrids were approximately 2–6 kb. This size was consistent within the same organs of the same species, as well as between species and F1 hybrids. Despite possessing relatively short telomere lengths compared to humans, the consistency of size among Xiphophorus species and organs may allow experimental detection of telomere shortening. The relative expression of telomerase reverse transcriptase (TERT) was determined by quantitative real-time PCR. Expression levels of TERT was measured in seven organs (ovary, testis, liver, gill, brain, heart, skin) from X. maculatus, X. hellerii and in control and ultraviolet light (UVB) exposed skin samples from X. maculatus, X. hellerii, and F1 interspecies hybrids. TERT gene expression was significantly higher in ovary and testis, while all other organs showed low relative TERT expression. Detectable increases in TERT expression were found in skin samples upon UVB exposure. Our findings suggest Xiphophorus may serve as a suitable model for future studies investigating the association of telomere length and telomerase expression in regard to aging and disease.

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“…The inner diameter of this structure is 26 Å, and its depth is 21Å; approximately corresponding to the size of the A-helix consisting of 8 bp. The DNA–RNA duplex located in the polymerase active site has precisely this type of structure [109]. The surface of the opening is a spiral structure consisting of positively charged amino acid residues.…”

Section: Telomerase Structurementioning

confidence: 99%

Telomere Lengthening and Other Functions of Telomerase

et al. 2012

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Telomerase is an enzyme that maintains the length of the telomere. The telomere length specifies the number of divisions a cell can undergo before it finally dies (i.e. the proliferative potential of cells). For example, telomerase is activated in embryonic cell lines and the telomere length is maintained at a constant level; therefore, these cells have an unlimited fission potential. Stem cells are characterized by a lower telomerase activity, which enables only partial compensation for the shortening of telomeres. Somatic cells are usually characterized by the absence of telomerase activity. Telomere shortening leads to the attainment of the Hayflick limit, the transition of cells to a state of senescence. The cells subsequently enter a state of crisis, accompanied by massive cell death. The surviving cells become cancer cells, which are capable both of dividing indefinitely and maintaining telomere length (usually with the aid of telomerase). Telomerase is a reverse transcriptase. It consists of two major components: telomerase RNA (TER) and reverse transcriptase (TERT). TER is a non-coding RNA, and it contains the region which serves as a template for telomere synthesis. An increasing number of articles focussing on the alternative functions of telomerase components have recently started appearing. The present review summarizes data on the structure, biogenesis, and functions of telomerase.

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Telomerase as a DNA-Dependent DNA Polymerase

Cited by 11 publications

References 55 publications

New Models of Tetrahymena Telomerase RNA from Experimentally Derived Constraints and Modeling

New Models of Tetrahymena Telomerase RNA from Experimentally Derived Constraints and Modeling

Characterization of telomeres and telomerase expression in Xiphophorus

Telomere Lengthening and Other Functions of Telomerase

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