Author： Chang P-W Zhang Q-M Takatori K Tachibana A Yonei S
Publisher： Informa Healthcare
ISSN： 1362-3095
Source： International Journal of Radiation Biology, Vol.81, Iss.2, 2005-02, pp. : 115-123
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Abstract
Purpose : In order to clarify the cellular processing and repair mechanisms for radiation-induced clustered DNA damage, we examined the correlation between the levels of DNA glycosylases and the sensitivity to ionizing radiation in Escherichia coli . Materials and methods : The lethal effects of ?-rays, X-rays, a-particles and H2O2 were determined in E. coli with different levels of DNA glycosylases. The formation of double-strand breaks by post-irradiation treatment with DNA glycosylase was assayed with ?-irradiated plasmid DNA in vitro . Results : An E. coli mutM nth nei triple mutant was less sensitive to the lethal effect of sparsely ionizing radiation (?-rays and X-rays) than the wild-type strain. Overproduction of MutM (8-oxoguanine-DNA glycosylase), Nth (endonuclease III) and Nei (endonulease VIII) increased the sensitivity to ?-rays, whereas it did not affect the sensitivity to a-particles. Increased sensitivity to ?-rays also occurred in E. coli overproducing human 8-oxoguanine-DNA glycosylase (hOgg1). Treatment of ?-irradiated plasmid DNA with purified MutM converted the covalently closed circular to the linear form of the DNA. On the other hand, overproduction of MutM conferred resistance to H2O2 on the E. coli mutM nth nei mutant. Conclusions : The levels of DNA glycosylases affect the sensitivity of E. coli to ?-rays and X-rays. Excessive excision by DNA glycosylases converts nearly opposite base damage in clustered DNA damage to double-strand breaks, which are potentially lethal.
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