Role of the Srs2 helicase and Ctf18 clamp loader in replication of structure-forming CAG repeats in S. cerevisiae
Nguyen, Jennifer.
2017-04-19T18:07:27.381Z
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Abstract: Our genome is riddled with repetitive sequences. While the functions of these repetitive sequences largely remain elusive, expansions of a subset of structure-forming microsatellites have been found to be associated with the onset of several neurodegenerative diseases. These repeat sequences pose a natural threat to the cell during replication and repair, forming barriers that can interf... read moreere with these processes that need to occur with high fidelity to faithfully transmit and maintain genetic information. The structure-forming nature of these repetitive sequences can lead to genomic instability: expansions, contractions, chromosomal breakage and fork stalling, and therefore they need to be properly maintained to prevent damage. This work has characterized the roles of the Srs2 helicase and the Ctf18 clamp loader in maintaining repeat integrity. Srs2 and Ctf18 have previously been shown to have a general role in genome maintenance, but also a specialized role in repeat protection. We have found that the Rad51 displacement activity of Srs2 is needed to prevent repeat instability but is dispensable in preventing repeat fragility. Srs2 helicase activity and PCNA interaction are needed to prevent repeat fragility. RTEL1, a human anti-recombinase helicase, is capable of complementing some srs2Δ repeat-specific mutant phenotypes in S. cerevisiae, providing support that it is a potential human ortholog of Srs2. The alternative clamp loader Ctf18 is needed to prevent repeat fragility and in its absence, Srs2 recruitment through PCNA interaction is vital. We hypothesize that Ctf18 is preventing repeat fragility by unloading/loading PCNA when a hairpin structure is encountered. Alternatively, Srs2 hairpin unwinding can prevent repeat fragility. The absence of both of these pathways leads to a synergistic increase in fragility. This work has contributed to the understanding of how cells cope with replication and repair through repetitive sequences, which our genome is mostly composed of.
At the request of the author, this graduate work is not available to view in the Tufts Digital Library until June 1, 2019.
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Biology.
Advisor: Catherine Freudenreich.
Committee: Juliet Fuhrman, Mitch McVey, Sergei Mirkin, and Susan Lovett.
Keywords: Biology, Molecular biology, and Genetics.read less - ID:
- fb494m72f
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