Role of the Srs2 helicase and Ctf18 clamp loader in replication of structure-forming CAG repeats in S. cerevisiae
Nguyen, Jennifer.
2016
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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 in... read moreterfere 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.
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
- Component ID:
- tufts:21265
- To Cite:
- DCA Citation Guide EndNote
