부산대학교 도서관

The effects of 222 Rn were measured in mouse L5178Y (LY) lymphoblasts that differ in repair capabilities. Line LY-S1 is deficient in the repair of X-radiation-induced DNA double-strand breaks, while lines LY-R16 and LY-R83 are presumed to be deficient in the excision of UV-radiation-induced pyrimidine dimers. Line LY-R83 is hemizygous while the other two lines are heterozygous at the thymidine kinase (tk) locus. After exposure to radon the $D_{0}\text{'}{\rm s}$ were found to be very similar for the three lines (0.30-0.31 Gy), whereas for X radiation the D0 for line LY-S1 is lower (0.7 Gy) than that for the two LY-R lines (1.3 Gy). Mutant frequencies at the tk locus were higher per gray after treatment with radon than X radiation, but at equitoxic doses the mutant frequencies were similar for X and α-particle radiation. A low radon-induced mutant frequency was observed for the hemizygous line, in agreement with the hypothesis that multilocus lesions were induced by the α-particle radiation and that mutants bearing intergenic lesions were not recovered in the ${\rm TK}^{+/-}$ line. The entire active tk allele was lost by 81% of the ${\rm TK}^{-/-}$ mutants of line LY-R16. In lines LY-S1 and LY-R16, 39-43% of the ${\rm TK}^{-/-}$ mutants exhibited loss of galactokinase activity, indicating that the mutational lesion inactivating the tk gene frequently extended to the neighboring galactokinase gene.