Telomeres, the ends of eukaryotic chromosomes, are a crucial link in understanding carcinogenesis and cellular sensescence in humans. Telomeres are composed of tandem arrays of a short repeat (TTAGGG in humans) that serve as binding sites for proteins that protect the ends from degradation and fusion. Because telomeres cannot be fully replicated, some sequence can be lost from their ends each time a cell divides. This is normally averted by telomerase, a ribonucleoprotein enzyme that adds copies of the telomeric repeat onto chromosome ends. Much evidence indicates that telomere shortening underlies the limited proliferative capacity of normal human somatic cells (which have little or no telomerase). Immortal human cancers show a restored ability to maintain telomeres. In most cases, this restoration is associated with restored telomerase activity, but in some cases involve an alternative, recombination-independent form of telomere maintenance called ALT. In this application, a powerful yeast system, Kluyveromyces lactis, is utilized to understand how recombinational telomere elongation (RTE) occurs. Recent work has suggested that the RTE that happens in K. lactis mutants lacking telomerase occurs through a 'roll and spread'mechanism whereby a tiny circle of telomeric DNA (t-circle) is first copied by a rolling circle mechanism to make the first elongated telomere, followed by other telomeres copying sequence from that telomere. This proposal aims to do further experiments to characterize how RTE occurs, including an alternate type of RTE which produces extreme telomere elongation especially similar to what occurs in human ALT cells. Other experiments will be done to determine precisely which features permit a telomere to be 'capped'and lengthened by telomerase and which cause uncapping and trigger repair through recombination or non- homologous end joining. Still other work will test the hypothesis that t-circles are derived from a strand- invaded telomeric end (t-loop) that undergoes an intramolecular deletion event and test whether dysfunctional telomeres perturb recombinational repair throughout the genome.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM061645-08
Application #
7617121
Study Section
Molecular Genetics C Study Section (MGC)
Program Officer
Carter, Anthony D
Project Start
2000-09-01
Project End
2011-05-31
Budget Start
2009-06-01
Budget End
2010-05-31
Support Year
8
Fiscal Year
2009
Total Cost
$277,137
Indirect Cost
Name
University of Georgia
Department
Genetics
Type
Schools of Arts and Sciences
DUNS #
004315578
City
Athens
State
GA
Country
United States
Zip Code
30602
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Xu, Jianing; McEachern, Michael J (2012) Maintenance of very long telomeres by recombination in the Kluyveromyces lactis stn1-M1 mutant involves extreme telomeric turnover, telomeric circles, and concerted telomeric amplification. Mol Cell Biol 32:2992-3008
Hsu, Min; Yu, Eun Young; Sprusansky, Ondrej et al. (2012) Functional analysis of the single Est1/Ebs1 homologue in Kluyveromyces lactis reveals roles in both telomere maintenance and rapamycin resistance. Eukaryot Cell 11:932-42
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Guo, Leilei; Zhang, Dong; Wang, Yingfeng et al. (2011) TRFolder: computational prediction of novel telomerase RNA structures in yeast genomes. Int J Bioinform Res Appl 7:63-81
Bechard, Laura H; Jamieson, Nathan; McEachern, Michael J (2011) Recombination can cause telomere elongations as well as truncations deep within telomeres in wild-type Kluyveromyces lactis cells. Eukaryot Cell 10:226-36
Basenko, Evelina; Topcu, Zeki; McEachern, Michael J (2011) Recombination can either help maintain very short telomeres or generate longer telomeres in yeast cells with weak telomerase activity. Eukaryot Cell 10:1131-42
Basenko, Evelina Y; Cesare, Anthony J; Iyer, Shilpa et al. (2010) Telomeric circles are abundant in the stn1-M1 mutant that maintains its telomeres through recombination. Nucleic Acids Res 38:182-9
Wang, Zhi-Ru; Guo, Leilei; Chen, Lizhen et al. (2009) Evidence for an additional base-pairing element between the telomeric repeat and the telomerase RNA template in Kluyveromyces lactis and other yeasts. Mol Cell Biol 29:5389-98
Cesare, Anthony J; Groff-Vindman, Cindy; Compton, Sarah A et al. (2008) Telomere loops and homologous recombination-dependent telomeric circles in a Kluyveromyces lactis telomere mutant strain. Mol Cell Biol 28:20-9

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