Giaccia A J, MacLaren R A, Denko N, Nicolaou D, Stamato T D
Wistar Institute of Anatomy and Biology, Philadelphia, PA 19104.
Mutat Res. 1990 Jul;236(1):67-76. doi: 10.1016/0921-8777(90)90034-3.
Repair or misrepair of DNA double-strand breaks (DSBs) is critical in determining cellular survival after gamma-irradiation. In this report, we focus on the cellular and biochemical consequences of restriction enzyme induced DSBs in wild-type Chinese hamster ovary (CHO) cells and the DNA DSB repair-defective mutant XR-1. We find that XR-1 possesses reduced cellular survival after the introduction of restriction enzymes that produce either cohesive or blunt ends. XR-1's sensitivity to killing by restriction enzymes strongly mimics its response to gamma-rays. Using pulsed field electrophoresis, we find that for each enzyme, similar numbers of DNA DSBs are being introduced in both cell lines. The simplest explanation for the increased sensitivity to restriction enzymes in the mutant is that the biochemical defect in XR-1 is not confined to the repair of ionizing radiation induced ends, but extends to DSBs that possess ligatable 3'-hydroxyl and 5'-phosphate ends as well.
DNA双链断裂（DSB）的修复或错误修复对于确定γ射线照射后的细胞存活至关重要。在本报告中，我们重点研究了野生型中国仓鼠卵巢（CHO）细胞和DNA DSB修复缺陷型突变体XR-1中限制性内切酶诱导的DSB的细胞和生化后果。我们发现，在引入产生粘性末端或平端的限制性内切酶后，XR-1的细胞存活率降低。XR-1对限制性内切酶杀伤的敏感性与其对γ射线的反应非常相似。使用脉冲场电泳，我们发现对于每种酶，两种细胞系中引入的DNA DSB数量相似。突变体对限制性内切酶敏感性增加的最简单解释是，XR-1中的生化缺陷不仅限于电离辐射诱导末端的修复，还扩展到具有可连接的3'-羟基和5'-磷酸末端的DSB。
