| 1. |
- Karademir Andersson, Ahu, et al.
(författare)
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Multiple DNA Interactions Contribute to the Initiation of Telomerase Elongation
- 2017
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Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836. ; 429:14, s. 2109-2123
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Tidskriftsartikel (refereegranskat)abstract
- Telomerase maintains telomere length and chromosome integrity by adding short tandem repeats of single-stranded DNA to the 3' ends, via reverse transcription of a defined template region of its RNA subunit. To further understand the telomerase elongation mechanism, we studied the primer utilization and extension activity of the telomerase from the budding yeast Naumovozyma castellii (Saccharomyces castellii), which displays a processive nucleotide and repeat addition polymerization. For the efficient initiation of canonical elongation, telomerase required 4-nt primer 3' end complementarity to the template RNA. This DNA-RNA hybrid formation was highly important for the stabilization of an initiation-competent telomerase-DNA complex. Anchor site interactions with the DNA provided additional stabilization to the complex. Our studies indicate three additional separate interactions along the length of the DNA primer, each providing different and distinct contributions to the initiation event. A sequence-independent anchor site interaction acts immediately adjacent to the base-pairing 3' end, indicating a protein anchor site positioned very close to the catalytic site. Two additional anchor regions further 5' on the DNA provide sequence-specific contributions to the initiation of elongation. Remarkably, a non-telomeric sequence in the distal 25- to 32-nt region negatively influences the initiation of telomerase elongation, suggesting an anchor site with a regulatory role in the telomerase elongation decision.
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| 2. |
- Karademir Andersson, Ahu, et al.
(författare)
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Naumovozyma castellii: an alternative model for budding yeast molecular biology
- 2017
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Ingår i: Yeast. - : Wiley. - 1097-0061 .- 0749-503X. ; 34:3, s. 95-109
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Tidskriftsartikel (refereegranskat)abstract
- Naumovozyma castellii (Saccharomyces castellii) is a member of the budding yeast family Saccharomycetaceae. It has been extensively used as a model organism for telomere biology research and has gained an increasing interest as a budding yeast model for functional analyses owing to its amenability to genetic modifications. Due to the suitable phylogenetic distance to S. cerevisiae the whole genome sequence of N. castellii has provided unique data for comparative genomic studies, and it played a key role in the establishment of the timing of the whole genome duplication and the evolutionary events that took place in the subsequent genomic evolution of the Saccharomyces lineage. Here we summarize the historical background of its establishment as a laboratory yeast species, and the development of genetic and molecular tools and strains. We review the research performed on N. castellii, focusing on areas where it has significantly contributed to the discovery of new features of molecular biology and to the advancement of our understanding of molecular evolution.
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| 3. |
- Karademir Andersson, Ahu
(författare)
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Studies of molecular mechanisms of telomere maintenance in Naumovozyma castellii
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Telomeres are special DNA-protein structures that protect ends of chromosomes from being recognized as double-strand breaks. Telomeres consist of tandemly repeated units of TG-rich DNA and associate with telomere-specific proteins.When a cell replicates its chromosomes, a certain piece of DNA is lost from chromosomal ends due to the ´´ end replication problem´´. This progressive shortening of telomeric sequences leads to inability of the chromosomal ends to distinguish themselves from double-stranded breaks. When a cell reaches to this crisis point, its proliferation will stop, leading to replicative senescence and eventually apoptosis. The most common way to counteract telomere loss is utilization of telomerase enzyme. Telomerase extends telomeres by using its intrinsic RNA template. Telomerase is active in human germ cells, cancer cells and certain eukaryotic species including the budding yeast Naumovozyma castellii. Most cancers cells (85-90 %) gain cellular immortality by re-activating the telomerase enzyme. The remaining cancer cells use alternative ways to restore lengths of their telomeres.In my doctoral studies I investigated molecular mechanisms of telomere maintenance in N. castellii. We reviewed the historical background of its establishment as a model organism and summarized its significant contributions to understanding of various molecular biological pathways. We developed stable haploid strains, which are amenable for genetic studies, to study telomerase-independent telomere maintenance. We characterized N. castellii telomerase regarding to its substrate specificity and priming capacity. We proposed a model where four different interactions occur, influencing the initiation of its priming capacity. We have showed the anchoring DNA regions that influence the initiation of telomere extension. Lastly, we investigated how telomeres are maintained when telomerase is disabled. Surprisingly, telomerase-negative cells proliferate without a detectable growth crisis. We showed that they maintain a short stretch of telomeric seqeunce at the very ends of chromosomes and also wild type structural organization at the chromosomal ends.In conclusion, I investigated the telomere maintenance from two different perspectives. These parallel studies contributed to understanding of the dynamics of telomere maintenance. Moreover, they emphasized conserved features of telomere biology, helping visualizing the evolutionary origins of telomerase and maintenance of linear chromosomes.
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