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N-Acetyltransferase Mpr1 of Saccharomyces cerevisiae can reduce intracellular oxidation levels and protect yeast cells under oxidative stress, including H(2)O(2), heat-shock, or freeze-thaw treatment. Unlike many antioxidant enzyme genes induced in response to oxidative stress, the MPR1 gene seems to be constitutively expressed in yeast cells. Based on a recent report that ethanol toxicity is correlated with the production of reactive oxygen species (ROS), we examined here the role of Mpr1 under ethanol stress conditions. The null mutant of the MPR1 and MPR2 genes showed hypersensitivity to ethanol stress, and the expression of the MPR1 gene conferred stress tolerance. We also found that yeast cells exhibited increased ROS levels during exposure to ethanol stress, and that Mpr1 protects yeast cells from ethanol stress by reducing intracellular ROS levels. When the MPR1 gene was overexpressed in antioxidant enzyme-deficient mutants, increased resistance to H(2)O(2) or heat shock was observed in cells lacking the CTA1, CTT1, or GPX1 gene encoding catalase A, catalase T, or glutathione peroxidase, respectively. These results suggest that Mpr1 might compensate the function of enzymes that detoxify H(2)O(2). Hence, Mpr1 has promising potential for the breeding of novel ethanol-tolerant yeast strains.

N-Acetyltransferase Mpr1 of Saccharomyces cerevisiae can reduce intracellular oxidation levels and protect yeast cells under oxidative stress. We found that yeast cells exhibited increased levels of reactive oxygen species during freezing and thawing. Gene disruption and expression experiments indicated that Mpr1 protects yeast cells from freezing stress by reducing the intracellular levels of reactive oxygen species. The combination of Mpr1 and l-proline could further enhance the resistance to freezing stress. Hence, Mpr1 as well as l-proline has promising potential for the breeding of novel freeze-tolerant yeast strains.

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