X-Ray-Induced Base Sequence Damage in Primate Alphoid DNA

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Abstract
Radiation-induced single-strand breaks were found throughout the 172 bp repeat units of African green monkey component .alpha.DNA. Two kinds of 3''-ends of 5''-32P-labeled restriction fragments were found, as previously described by others. After irradiation in vitro, the yield of single-strand breaks was 4 .times. 10-5 breaks/nucleotide/Gy, as determined by analyses in DNA sequencing type gels. Protection from X-ray damage was found when the DNA received 150 Gy in the presence of 2-mercaptoethanol. The results demonstrate a very sensitive quantitative means to study the role of indirect effects of ionizing radiation on strand-break induction and protection at the base sequence level. Component .alpha.DNA was isolated from irradiated CV-1 cells and was analyzed for single-strand breaks. Under these conditions the frequency of breaks was less than the frequency obtained when purififed DNA was irradiated. The methodology is presented because of its relevance to the study of DNA strand breakage in living cells.