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Telomere Regulation and Heterochromatin Formation in Yeasts

Wang, Jinyu
http://rave.ohiolink.edu/etdc/view?acc_num=case1474025783681296

Abstract Details

, Doctor of Philosophy, Case Western Reserve University, Genetics.
Telomeres, the ends of eukaryotic chromosomes, consist of repetitive DNA sequences and telomere-binding proteins that protect the end from the DNA damage response. Telomerase adds new telomere DNA repeats to the ends to prevent loss of genetic material. In the budding yeast Saccharomyces cerevisiae, short telomeres are preferentially elongated by telomerase. Tel1, the yeast homolog of human ATM kinase, is preferentially recruited to short telomeres and its kinase activity is required for telomere elongation. Rif1, a telomere binding protein, negatively regulates telomere length by interacting with other telomere binding proteins to block telomerase recruitment and has 14 consensus phosphorylation sites for Tel1. I therefore hypothesized that Tel1 phosphorylation of Rif1 allowed telomere elongation by telomerase. To test this hypothesis, I first took a candidate approach by mutating the putative Rif1 phosphorylation sites and found that these mutants altered telomere length. None of the mutants tested altered the response to DNA damage agents. Mass spectrometry analysis identified many Rif1 phosphorylation sites, and some of these sites had increased levels of phosphorylation or were only phosphorylated in cells with short damaged telomeres, including a Tel1 consensus site. These data led to a revised model for Rif1 phosphorylation to regulate telomere length in S. cerevisiae. Heterochromatin domains play important roles in chromosome biology, organismal development and aging. In the fission yeast Schizosaccharomyces pombe and metazoans, heterochromatin is marked by dimethylation of histone H3 lysine 9. While the factors required for heterochromatin have been identified, the dynamics of heterochromatin formation are poorly understood, especially at telomeres. Telomeres convert adjacent chromatin into silenced heterochromatin, but whether heterochromatin domain formation occurs within the first cell cycle of telomere formation or over many generations was unknown. To form a new telomere in S. pombe cells, a new rapidly inducible DNA double-strand break (DSB) system was generated and the DSB was placed next to telomere repeats in a region of euchromatin. The induced DSB resulted in immediate telomere formation, telomere elongation and the gradual spreading of heterochromatin. However, spreading was highly dynamic after the telomere had reached its stable length. The system also allowed the discovery of new failsafe mechanism where a DSB lacking telomere repeats adjacent to the subtelomeric region was rapidly and efficiently healed by recombination with a new telomere, in contrast to a DSB at a centromeric locus that caused growth arrest. Telomere formation in S. pombe therefore reveals novel aspects of heterochromatin dynamics and discovers a failsafe mechanism to repair subtelomeric breaks.
Kurt Runge (Advisor)
Ahmad Khalil (Committee Chair)
Peter Scacheri (Committee Member)
Derek Taylor (Committee Member)
Bibo Li (Committee Member)
Genetics; Molecular Biology
Telomere length regulation, Rif1, Phosphorylation, Saccharomyces cerevisiae, Telomere formation, Heterochromatin spreading, Chromosome healing, Schizosaccharomyces pombe

Recommended Citations

Citations

  • Wang, J. (n.d.). Telomere Regulation and Heterochromatin Formation in Yeasts [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1474025783681296

    APA Style (7th edition)

  • Wang, Jinyu. Telomere Regulation and Heterochromatin Formation in Yeasts. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1474025783681296.

    MLA Style (8th edition)

  • Wang, Jinyu. "Telomere Regulation and Heterochromatin Formation in Yeasts." Doctoral dissertation, Case Western Reserve University. Accessed APRIL 19, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=case1474025783681296

    Chicago Manual of Style (17th edition)

case1474025783681296
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This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.