Increased DNA double strand breakage is responsible for sensitivity of thepso3-1 mutant of Saccharomyces cerevisiae to hydrogen peroxide

Escherichia coli endonuclease III (endo III) is the key repair enzyme essen tial for removal of oxidized pyrimidines and abasic sites. Although two hom ologues of endo III, Ntg1 and Ntg2, were found in Saccharomyces cerevisiae, they do not significantly contribute to repair of oxidative DNA damage in vivo. This suggests that an additional activity(ies) or a regulatory pathwa y(s) involved in cellular response to oxidative DNA damage may exist in yea st. The pso3-1 mutant of S. cerevisiae was previously shown to be specifica lly sensitive to toxic effects of hydrogen peroxide (H2O2) and paraquat. He re, we show that increased DNA double strand breakage is very likely the ba sis of sensitivity of the pso3-1 mutant cells to H2O2. Our results, thus, i ndicate an involvement of the Pso3 protein in protection of yeast cells fro m oxidative stress presumably through its ability to prevent DNA double str and breakage. Furthermore, complementation of the repair defects of the pso 3-1 mutant cells by E. coli endo III has been examined. It has been found t hat expression of the nth gene in the pso3-1 mutant cells recovers survival , decreases mutability and protects yeast genomic DNA from breakage followi ng H2O2 treatment. This might suggest some degree of functional similarity between Pso3 and Nth. (C) 2001 Elsevier Science B.V. All rights reserved.