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


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.
Skorvaga
M
M
Laboratory of Molecular Genetics, Cancer Research Institute, Slovak Academy of Sciences, Vlárska 7, 833 91 Bratislava 37, Slovak Republic.
Cernáková
L
L
Chovanec
M
M
Vlasáková
D
D
Kleibl
K
K
Hendry
J H
JH
Margison
G P
GP
Brozmanová
J
J
D002470:Cell Survival / Q000187:drug effects* / Q000528:radiation effects*; D004249:DNA Damage / Q000502:physiology; D043224:Deoxyribonuclease (Pyrimidine Dimer) / Q000235:genetics* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004351:Drug Resistance / Q000502:physiology; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000528:radiation effects; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects / Q000528:radiation effects; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D016297:Mutagenesis, Site-Directed; D011836:Radiation Tolerance / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects*; D014170:Transformation, Genetic
D029968:Escherichia coli Proteins; D006861:Hydrogen Peroxide; D043224:Deoxyribonuclease (Pyrimidine Dimer); C106403:NTH protein, E coli