Repair of Damage in Double-stranded ϕX174 (RF) DNA Due to Radiation-induced Water Radicals

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Abstract
Experiments in which the yields of radiation-induced OH and H radicals were varied, showed that both types of water radicals inactivate .vphi.X174 RF DNA to about the same extent as measured by transfection of the (irradiated) DNA to [Escherichia coli] wild-type spheroplasts. on the other hand, using spheroplasts prepared from E. coli strains, deficient in one of the proteins involved in excision DNA repair (uvrA- or uvrC-) or in post-replication repair (recA-), clear differences between damage originating from OH or H radical attack were found. Part of the radiation damage due to H radicals appeared to be repairable by an uvrA-gene-dependent repair mechanism, whereas this repair pathway does not play an important role in the case of OH radical damage. The reverse applies to uvrC-gene-dependent repair, which only affects OH radical damage (obtained under anoxic conditions), but has no influence on damage due to H radicals. Irradiation of double-stranded phage .vphi.X174 (RF) DNA in the presence of O2 however, yields damage, due to OH radicals only, which appeared not to be sensitive to either uvrC- or uvrA-gene-dependent repair. Furthermore, post-replication repair (recA) has only very little effect on the amount of inactivation by H or OH radicals, when irradiation is carried out under anoxic conditions. Significant inactivation due to hydrated electrons, whether the biological activity was determined by use of wild-type spheroplasts or of strains deficient in excision or post-replication repair proteins, was not found.
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