Homologous Recombination is Activated at Early Time Points Following Exposure to Cobalt Chloride Induced Hypoxic Conditions in Saccharomyces cerevisiae

DNA repair functions are essential for the maintenance of genetic integrity and are regulated in response to both environmental and chemical stressors in mammalian and yeast cells in culture. The inhibitory effect of limited O₂ availability on DNA repair functions in general and on homologous recombination (HR) in particular, correlates with increased chromosomal abnormalities in hypoxic cancer cells. Given the above, we have investigated the effects of CoCl₂,––a hypoxia mimetic agent on HR and genetic aberrations in Saccharomyces cerevisiae. Our studies demonstrate that both acute and chronic exposure to CoCl₂ activated HR and increased genetic aberrations in S. cerevisiae D7 cells. At early time points following addition of CoCl₂ to the growth media, cells were briefly arrested in the G1-S boundary concomitant with a transient increase in Rad52-GFP foci formation and induction of low levels of DNA damage. The mode of action of CoCl₂ is thus similar to that of DNA synthesis inhibitors, the later are known to induce HR and cause G1-S arrest. We propose that the activation of HR in the presence of the hypoxia mimetic agent may be attributed to the replication stress and/or DNA damage induced by the stressor.