INDUCIBILITY OF THE RESPONSE OF YEAST-CELLS TO PEROXIDE STRESS

Exponential phase cells of the yeast Saccharomyces cerevisiae when treated with a non-lethal concentration of hydrogen peroxide (H2O2; 0.2 mM) for 60 min adapted to become resistant to the lethal effects of a higher dose of H2O2 (2 mM). From studies using cycloheximide to inhibit protein synthesis it appears that protein synthesis is required for maximal induction of resistance but that some degree of protection from the lethal effects of peroxide can be acquired in the absence of protein synthesis. Treatment of cells with 50-mu-g cycloheximide ml-1 alone led to them acquiring some protection from peroxide. Cells subjected to heat shock became more resistant to 2 mM-H2O2; however, peroxide pretreatment did not confer thermotolerance. L-[S-35]Methionine labelling of cells subjected to 0.2 mM-H2O2 stress showed that synthesis of at least ten polypeptides was induced by peroxide treatment. Some of these were also induced in cells subjected to heat shock (23 to 37-degrees-C shift) but the synthesis of at least four polypeptides (45, 39.5, 38 and 24 kDa) was unique to peroxide-stressed cells. Resistance to peroxide was also inducible in an isogenic petite and an isogenic strain with a mutation in the HAP1 gene, indicating that the adaptive response does not require functional mitochondria.