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 (77994B) 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.

• PMID: 14703947
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Journal Article | Research Support, Non-U.S. Gov't

Authors

Skorvaga M, Cernáková L, Chovanec M, Vlasáková D, Kleibl K, Hendry JH, Margison GP, Brozmanová J

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