Date Approved


Degree Type

Open Access Senior Honors Thesis

Department or School


First Advisor

Anne Casper

Second Advisor

Aaron Liepman

Third Advisor

Marianne Laporte


Several subtypes of double-strand break repair (DSB repair) exist, with the Rad51 dependent canonical break-induced replication (BIR) pathway being extremely well documented. In contrast, little is known about the error-prone Rad51 independent DSB repair pathway called microhomology-mediated break-induced replication (mmBIR). The purpose of this study was to test the hypothesis that manipulation of the SGS1 gene in Saccharomyces cerevisiae will influence the type of DSB repair, more specifically, the amount of repair done by canonical BIR and mmBIR. A mutant, sgs1-FD, was previously documented to show no interaction with Rad51p. The interaction between Sgs1p and Rad51p is integral to the functioning of the canonical BIR pathway. As such, we suspected in these mutants that the Rad51-independent pathway, mmBIR would be more prevalent than canonical BIR since loading of Rad51p would be limited. We also predicted homologous recombination would decrease with this mutant since Sgs1p is needed. Strains that underwent repair events were categorized using SNP markers, CHEF gels, and next-generation sequencing. Surprisingly, we found that the sgs1-FD mutant experienced a higher proportion of homologous recombination when under moderate replication stress, but a reduction in the proportion of gene conversions. Additionally, mmBIR was not found to be more prevalent than canonical BIR in sgs1-FD mutants. We hypothesize that Srs2p may act redundantly with Sgs1p protein in the process of loading Rad51p onto a ssDNA overhang for homology search since Srs2p shares some of the same functions as Sgs1p.

Included in

Biology Commons