LeDoux S P, Thangada M, Bohr V A, Wilson G L
Department of Structural and Cellular Biology, University of South Alabama, Mobile 36688.
Cancer Res. 1991 Feb 1;51(3):775-9.
The repair of DNA damage induced by methylnitrosourea (MNU) in restriction fragments containing the dihydrofolate reductase (DHFR) gene in Chinese hamster ovary cells was compared to that in equal size restriction fragments containing a nontranscribed flanking sequence 3' to the DHFR gene or the c-fos gene. Following exposure to 10(-3) M MNU, restriction fragments containing either the DHFR gene or the 3' flanking sequence had similar amounts of alkali labile sites, approximately 2 sites/restriction fragment. Fragments encompassing the c-fos gene had less than 2 breaks/fragment. Twenty-four h after exposure to MNU a consistent, but slight and not statistically significant, difference was seen with more adducts removed from the DHFR gene than the 3' flanking sequence. No repair was detected in the c-fos containing fragments. In addition, the repair of N7-methylguanine in the overall genome was assessed by use of a 32P end-labeling technique. Seventy % of this major alkylation product was repaired after 24 h. These findings establish that repair heterogeneity occurs in Chinese hamster ovary cells after exposure to MNU.
将中国仓鼠卵巢细胞中含有二氢叶酸还原酶（DHFR）基因的限制片段中由甲基亚硝基脲（MNU）诱导的DNA损伤修复情况，与含有DHFR基因3'端非转录侧翼序列或c-fos基因的等大小限制片段中的修复情况进行了比较。暴露于10⁻³ M MNU后，含有DHFR基因或3'侧翼序列的限制片段具有相似数量的碱不稳定位点，约为2个位点/限制片段。包含c-fos基因的片段断裂数少于2个/片段。暴露于MNU 24小时后，观察到一种一致但轻微且无统计学意义的差异，即从DHFR基因中去除的加合物比3'侧翼序列更多。在含有c-fos的片段中未检测到修复。此外，通过使用³²P末端标记技术评估了整个基因组中N⁷-甲基鸟嘌呤的修复情况。24小时后，这种主要烷基化产物的70%得到了修复。这些发现表明，中国仓鼠卵巢细胞在暴露于MNU后会发生修复异质性。
