Date Approved

2020

Degree Type

Open Access Senior Honors Thesis

Department or School

Biology

First Advisor

Dr. Anne Caper

Second Advisor

Dr. Aaron Liepman

Third Advisor

Dr. Marianne Laporte

Abstract

Common fragile sites are large chromosomal regions that are especially prone to double-strand breaks and are associated with cancer progression. We are studying how breaks at Fragile Site 2 (FS2), on Saccharomyces cerevisiae chromosome III, are repaired. Rad51p is a DNA-binding protein involved in DNA repair pathways. We hypothesize that the rad51Δ mutation, which results in complete loss of Rad51p, will promote the use of the error-prone mmBIR repair pathway. Because Rad51p is involved in higher fidelity repair pathways, we expect other repair pathways to be used when it is absent. Breaks were induced at FS2 in rad51Δ mutant diploids and repair events were characterized in cultures that underwent DNA repair. We categorized repair events by testing three single nucleotide polymorphisms (SNPs). We determined the chromosome size by performing CHEF gel electrophoresis and Southern blotting on isolated chromosomal DNA. We determined the sequence of the entire genome and further analyzed each repair event using next-generation paired-end sequencing. Contrary to our hypothesis, the results of this study suggest that the loss of Rad1p does not significantly increase the frequency of repair events by mmBIR. The findings of this study suggest that Rad51p does not play a significant role in cellular choice of repair pathways. Moreover, because no mmBIR was observed in rad51 mutants, this is consistent with the possibility that Rad51p may be needed in the mmBIR pathway.

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