Telomere elongation and de novo formation by telomerase from hypotrich ciliates /
Telomeres are the essential protein-DNA structures found at the termini of linear eukaryotic chromosomes. They are synthesized by a unique ribonucleoprotein reverse transcriptase, telomerase. The enzyme consists of RNA and protein components, both of which are involved in telomere synthesis. Telo...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1996.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=739669531&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Telomeres are the essential protein-DNA structures found at the termini of linear eukaryotic chromosomes. They are synthesized by a unique ribonucleoprotein reverse transcriptase, telomerase. The enzyme consists of RNA and protein components, both of which are involved in telomere synthesis. Telomerase serves a dual role at chromosome ends. It can maintain tracts of telomere repeats as well as form telomeres de novo on broken chromosomes in a process called chromosome healing. This study used the hypotrich ciliates, Oxytricha nova and Euplotes crassus as model systems to investigate the templating function of the telomerase RNA and to study the process of developmentally-regulated de novo telomere formation. Oxytricha and Euplotes telomerases both synthesize T4G4 telomeric arrays. However, the telomerase RNA components, both 190 nucleotides in length, have diverged in sequence and templating function. Based on the ability of telomerase RNA antisense oligonucleotides to inhibit or prime telomere synthesis, ii: was demonstrated that the Oxytricha template comprises residues 42 to 50 in the RNA. This is in contrast to the Euplotes telomerase, which uses residues 37 to 45 to template T4G4 addition. Euplotes is an ideal organism to study chromosome healing by telomerase because it undergoes a massive developmentally regulated chromosome fragmentation and de novo telomere addition event. Chimeric primers, consisting of both telomeric and nontelomeric sequence, were used to define two pathways by which telomerase processes the nontelomeric 3' ends of DNA. The first pathway, referred to as default, initiates synthesis independently of Watson-Crick basepairing of the primer to the RNA template and results in the direct addition of telomeres to nontelomeric DNA. The second pathway is initiated with the endonucleolytic removal of 3' residues from the primer to expose an upstream, internal telomeric sequence for nucleotide addition. Cells undergoing development can process DNA in both pathways, whereas vegetative cells only utilize cleavage-initiated telomere addition to process nontelomeric DNA. Partial purification of telomerase from developing cells resulted in the loss of the default mode of telomere addition. We propose telomerase in ciliates is developmentally-regulated, capable of catalyzing specific reactions only during the appropriate time in development. |
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| Item Description: | Vita. "Major Subject: Biochemistry". |
| Physical Description: | xi, 262 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references: pages 197-218. |