The Human rad52-G59R Mutant Allele Confers a Hypomorphic Homologous Recombination Phenotype in Saccharomyces cerevisiae
Authors:Lauren Liddell, Shannon Owens
Mentor:Adam Bailis, Associate Professor, Molecular and Cellular Biology, City of Hope, Irell & Manella Graduate School of Biological Sciences
DNA double strand breaks (DSBs) are repaired by homologous recombination (HR) in order to prevent genome rearrangements or cell lethality. The human tumor suppressor genes, BRCA1 and BRCA2 promote the HR that circumvents genomic rearrangements, such as the translocations that are a hallmark of many cancers. RAD52, a gene conserved from yeast to humans has been implicated in HR in human cells, and, when lost acts synergistically with loss of the BRCA1 and BRCA2 genes. This suggests that RAD52 mediates distinct mechanisms of DSB repair by HR in human cells. This research describes the introduction of the human RAD52 gene (HsRAD52) into the budding yeast Saccharomyces cerevisiae in order to examine its ability to function in HR, which has been difficult to assess in mammalian cells. After demonstrating that HsRAD52 could complement loss of yeast RAD52 (ScRAD52) in an HR assay, we introduced Hsrad52-G59R, an allele isolated from a breast cancer patient. This allele encodes an amino acid substitution at a position that is conserved throughout phylogeny, and is in a region of the protein thought to be involved in DNA binding and the annealing of complementary single strands. Therefore, this mutation may affect HR and, perhaps, the genome stability of the patient. We found that a Scrad52 mutant strain containing the Hsrad52-G59R mutant allele displayed a 2.7-fold reduction in HR frequency relative to a strain containing the wild-type HsRAD52 gene. If the patient who had this mutant allele experienced a similar HR defect, this may have increased genome instability and promoted tumorigenesis.