Deletion of MAG1 and MRE11 enhances the sensitivity of the Saccharomyces cerevisiae HUG1P-GFP promoter-reporter construct to genotoxicity.

Eukaryotic yeast-based DNA damage cellular sensors offer many advantages to traditional prokaryotic-based mutagenicity assays. The HUG1P-GFP promoter-reporter construct has proven to be an effective method to selectively screen for multiple types of DNA damage. To enhance the sensitivity and selectivity of the system to different types of DNA damage, two genes involved in distinct DNA damage responses were deleted. Deletion of MAG1, a gene encoding a DNA glycosylase and member of the base excision repair (BER) pathway, increased the biosensor's sensitivity to the alkylating agents methyl methanesulfonate (MMS) (lowering the sensitivity threshold to 0.0001% (v/v)) and ethyl methanesulfonate (EMS). Deletion of MRE11, part of the highly conserved RMX complex that aids in sensing and repairing double strand breaks in budding yeasts, enhanced sensitivity to gamma radiation (gamma-ray) (detection threshold of 50Gy) and camptothecin. The mre11Delta phenotype dominated in mag1Deltamre11Delta strains. Through the deletions, we were able to engineer increased selectivity to alkylating agents, gamma-ray, and camptothecin, since increased sensitivity to one type of damage did not alter the quantitative response to other genotoxins. The enhancements to the HUG1P-GFP system did not affect its ability to detect several other DNA damaging agents, including 1,2-dimethyl hydrazine (SDMH), phleomycin, and hydroxyurea (HU), or affect its lack of response to the potentially non-genotoxic carcinogen formaldehyde.