Order effect of base excision processes to repair clustered DNA damage

Yokoya, Akinari; Shiraishi, Iyo; Shikazono, Naoya

In the present study, we investigate how the initial enzymatic repair affects the activity of the latter repair enzyme. Plasmid DNA (pUC18) irradiated with C ion is treated with two base excision repair enzymes, Nth and Fpg, which convert pyrimidine and purine lesions to a SSB. The enzymatic activities are quantified by measuring the conformational changes of the plasmid using agarose gel electrophoresis. Obtained results show that the amount of enzymatically induced SSB is slightly (about 5%) less in DNA sample treated with Nth first and then Fpg than that in the sample treated with Fpg first and then Nth, or with both enzymes simultaneously. The repairability of clustered damage induced by high-LET ions will be discussed.