MUTANTS OF SACCHAROMYCES-CEREVISIAE SENSITIVE TO OXIDATIVE AND OSMOTIC-STRESS

Although oxidative stress is involved in many human diseases, little i s known of its molecular basis in eukaryotes. In a genetic approach, S . cerevisiae was used to identify elements involved in oxidative stres s. By using hydrogen peroxide as an agent for oxidative stress, 34 mut ants were identified. All mutants were recessive and fell into 16 comp lementation groups (posl to pos16 for peroxide sensitivity). They corr esponded to single mutations as shown by a 2:2 segregation pattern. En zymes reportedly involved in oxidative stress, such as glucose-6-phosp hate dehydrogenase, glutathione reductase, superoxide dismutase, as we ll as glutathione concentrations, were investigated in wild-type and m utant-cells. One complementation group lacked glucose-6-phosphate dehy drogenase and was shown to be allelic to the glucose-6-phosphate dehyd rogenase structural gene ZWF1/MET19. In other mutants all enzymes supp osedly involved in oxidative-stress resistance were still present. How ever, several mutants showed strongly elevated levels of glutathione r eductase, gluconate-6-phospate dehydrogenase and glucose-6-phosphate d ehydrogenase. One complementation group, pos9, was highly sensitive to oxidative stress and revealed the same growth phenotype as the previo usly described yap1/par1 mutant coding for the yeast homologue of mamm alian transcriptional activator protein, c-Jun, of the proto-oncogenic AP-1 complex. However, unlike par1 mutants, which showed diminished a ctivities of oxidative-stress enzymes and glutathion level, the pos9 m utants did not reveal any such changes. In contrast to other recombina nts between pos mutations and par1, the sensitivity did not further in crease in par1 pos9 recombinants, which may indicate that both mutatio ns belong to the same regulating circuit. Interestingly, ten complemen tation groups were, in parallel, sensitive to osmotic stress, and one mutant allele revealed increased heat sensitivity. Our results indicat e that a surprisingly large number of genes seem to be involved in oxi dative-stress resistance and a possible overlap exists between osmotic stress and other stress reactions.