PROKARYOTIC IRON SUPEROXIDE-DISMUTASE REPLACES CYTOSOLIC COPPER, ZINCSUPEROXIDE-DISMUTASE IN PROTECTING YEAST-CELLS AGAINST OXIDATIVE STRESS

The iron superoxide dismutase (FeSOD) gene of Escherichia coli was clo ned in Saccharomyces cerevisiae cells deficient in copper,zinc superox ide dismutase (Cu,ZnSOD). FeSOD replaced Cu,ZnSOD in protecting the ye ast cells against oxidative stress. In the recombinant strains the FeS OD gene, which was under the transcriptional control of the yeast phos phoglycerate kinase gene promoter, was functionally expressed at two d ifferent levels on episomal and centromeric plasmids. Despite suppress ion of methionine and lysine auxotrophy, the higher level of FeSOD act ivity was more beneficial to growth of the mutant yeast cells only whe n these were exposed to higher levels of oxidative stress induced by p araquat or 100% oxygen. In the presence of paraquat, there was a novel stimulation of FeSOD activity. This was associated with a marked incr ease in catalase activity, and a decrease in glutathione reductase act ivity.