ESCHERICHIA-COLI IRON SUPEROXIDE-DISMUTASE TARGETED TO THE MITOCHONDRIA OF YEAST-CELLS PROTECTS THE CELLS AGAINST OXIDATIVE STRESS

A gene encoding a fusion protein consisting of Escherichia coli iron s uperoxide dismutase (FeSOD) with the mitochondrial targeting presequen ce of yeast manganese superoxide dismutase (MnSOD) was cloned and expr essed in E. coli and in Saccharomyces cerevisiae DL1Mn(-) yeast cells deficient in MnSOD. In the yeast cells the fusion protein was imported into the mitochondrial matrix. However, the presequence was not cleav ed. In a control set of experiments, the E. coli FeSOD gene without th e yeast MnSOD leader sequence was also cloned and expressed in S. cere visiae DL1Mn(-) cells. In this case the FeSOD was located in the cytos ol and was not imported into the mitochondrial matrix. E. coli FeSOD, with and without the yeast MnSOD presequence, proved to be active in y east, but, whereas the FeSOD targeted to the mitochondria of yeast cel ls deficient in MnSOD protected the cells from the toxic effects of ox idative stress, FeSOD without the yeast MnSOD presequence did not prot ect the yeast cells deficient in MnSOD against oxidative stress.