Split-dose Recovery Is Due to the Repair of DNA Double-strand Breaks

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Abstract
DNA double-strand breaks are the molecular lesions the repair of which leads to the reappearance of the shoulder observed in split-dose experiments. This conclusion is based on results obtained with the help of a diploid yeast mutant rad54-3 which is temperature-conditional for the repair of DNA double-strand breaks. Two repair steps must be met to yield the reappearance of the shoulder on a split-dose survival curve: the repair of double-strand breaks during the interval between 2 doses and on the nutrient agar plate after the 2nd dose. In yeast lethality may be attributable to either an unrepaired double-strand break (i.e., a double-strand break is a potentially lethal lesion) or to the interaction of 2 double-strand breaks (misrepair of double-strand breaks). Evidence is presented that the 2 cellular phenomena of liquid holding recovery (repair of potentially lethal damage) and of split-dose recovery (repair of sublethal damage) are based on the repair of the same molecular lesion, the DNA double-strand break.