Effect of expression of the Escherichia coli nth gene in Saccharomyces cerevisiae on the toxicity of ionizing radiation and hydrogen peroxide

Abstract

Purpose: To examine the contribution of endonuclease III (Nth)‐repairable lesions to the cytotoxicity of ionizing radiation (IR) and hydrogen peroxide (H₂O₂) in the yeast Saccharomyces cerevisiae.

Materials and methods: A selectable expression vector containing the E. coli nth gene was transformed into two different wild‐type strains (7799‐4B and YNN‐27) as well as one rad52 mutant strain (C5–6). Nth expression was verified by Western analysis. Colony‐forming assay was used to determine the sensitivity to IR and H₂O₂ in both stationary and exponentially growing cells.

Results: The pADHnth‐transformed wild‐type (7799‐4B) strain was considerably more resistant than vector‐only transformants to the toxic effects of IR, in both stationary and exponential growth phases, although this was not the case in another wild‐type strain (YNN‐27). In contrast, there were no significant effects of nth expression on the sensitivity of the wild‐type cells to H₂O₂. Moreover, nth expression caused no effects on the H₂O₂ sensitivity in the rad52 mutant cells, but it led to a slight increase in sensitivity in these cells following IR, particularly at the highest dose levels used.

Conclusions: Whilst other damage‐processing systems may play a role, DNA lesions that are substrates for Nth can also make a contribution to the toxic effects of IR in certain wild‐type yeast. Hence, DNA double‐strand breaks should not be considered the sole lethal lesions following IR exposure.