The repair of ionising-radiation-induced DNA double-strand break type damage was measured by Kohn neutral elution in an X-ray-sensitive mutant of V79-4, irs1. This was done in order to investigate further the likelihood that irs1 carries a defect which leads to error-prone repair of DNA damage, and not simply a reduced ability to rejoin DNA double-strand breaks. The mutant displayed an equal increase in sensitivity to the lethal effects of neutrons, as compared to X-rays. Both irs1 and V79-4 showed an increased sensitivity to the killing effects of neutrons of around 2 at 10% survival. irs1 also showed an exponential survival after either X-rays or neutrons. The induction of DNA double-strand breaks was measured in both cell lines over a dose range of 10-40 Gy using Kohn neutral filter elution. Induction of breaks by X-rays in irs1 seemed to increase slightly with dose, relative to induction in V79-4, so that at 40 Gy 1.5 times more DNA double-strand breaks were measured in irs1 cells than in V79-4. Neutron irradiation resulted in a more similar level of induction in either strain after 10-40 Gy. This difference in induction of damage may be due to a different cell-cycle composition in either cell line. The rejoining of X-ray induced double-strand breaks showed a very similar pattern (on a percentage rejoined basis) in both cell lines, although from the induction data at 40 Gy, the dose at which rejoining was measured, fewer breaks were rejoined in V79-4 but also fewer breaks remained unsealed. Neutron-induced breaks, however, were rejoined more efficiently in irs1 again on a percentage basis, but also in absolute terms since similar induction was seen after 40 Gy. This data, together with the differences seen in the rejoining of X-ray compared to neutron induced breaks, may indirectly support the proposal that irs1 is a misrepair mutant.

译文

电离辐射诱导的DNA双链断裂型损伤的修复是通过Kohn中性洗脱在V79-4的x射线敏感突变体irs1中进行的。这样做是为了进一步研究irs1携带缺陷的可能性,该缺陷导致容易出错的DNA损伤修复,而不仅仅是降低重新连接DNA双链断裂的能力。与x射线相比,该突变体对中子致死效应的敏感性相同。irs1和V79-4在10% 存活时对中子的杀伤作用均显示出增加的敏感性,约为2。irs1在x射线或中子后也显示出指数生存。使用Kohn中性滤镜洗脱在10-40 Gy的剂量范围内测量了两种细胞系中DNA双链断裂的诱导。相对于V79-4中的诱导,irs1中x射线对断裂的诱导似乎随剂量略有增加,因此在40 Gy时,irs1细胞中测得的DNA双链断裂比V79-4中多1.5倍。10-40 Gy后,中子辐照在任一菌株中的诱导水平均更为相似。损伤诱导的这种差异可能是由于两种细胞系中的细胞周期组成不同所致。X射线诱导的双链断裂的重新结合在两种细胞系中显示出非常相似的模式 (以百分比重新结合为基础),尽管从40 gy的诱导数据 (测量重新结合的剂量) 来看,在V79-4中重新结合的断裂更少,但仍保持未密封的断裂更少。然而,中子诱导的断裂在irs1中再次以百分比为基础更有效地重新结合,但也以绝对值重新结合,因为在40 Gy之后看到了类似的诱导。该数据以及与中子诱导的断裂相比,x射线重新结合所看到的差异,可能间接支持irs1是误修突变体的提议。

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