Effects of oxidative stress on mitotic recombination and genomic stability in yeast

Oxidative stress is a common factor threating genomic stability in almost all aerobic organisms. Using a yeast screening system, we measured the frequency of mitotic recombination was greatly elevated after H2O2 treatment. H2O2 was able to break chromatid directly in G1 synchronized cells and homologous recombination was induced to repair DNA double stand breaks at S/G2 phase. By whole genome SNP microarray and sequencing, the patterns of H2O2 induced loss of heterozygosity (LOH; gene conversion and crossover), chromosomal rearrangement, and aneuploidy changes were revealed. LOH events were the most common genomic alterations induced by H2O2 and were randomly distributed throughout the genome. JSC25 cells were grown in 7 mL YPD overnight to reach an OD600 of 0.2. Yeast cells (5×107) were collected by centrifugation and arrested in G1 in 1 mL YPD containing 2.5 μg α-factor at 300. After two hours, H2O2 was added into the cell culture. Cell culture was incubated at 300 for another hour. Yeast cells were then washed twice to remove α-factor and H2O2 before plating. Yeast cells were cultured at 300 for 3 days and sectored colonies were selected for whole genome SNP microarray analysis.