EFFECTS OF DOSE FRACTIONATION ON ULTRAVIOLET SURVIVAL OF ESCHERICHIA COLI
EFFECTS OF DOSE FRACTIONATION ON ULTRAVIOLET SURVIVAL OF ESCHERICHIA COLI
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DOI：
10.1111/j.1751-1097.1968.tb05831.x
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发表时间：
1968-01-01
影响因子：
3.3
通讯作者：
HARM, W
中科院分区：
文献类型：
--
作者：
HARM, W
将大肠杆菌B/r和B暴露在低平均剂量率（2537 A）的紫外线辐射下，无论是分次照射还是以极低剂量率（80尔格/平方毫米/小时）持续照射，都比单次暴露在高剂量率下的存活率要高得多。这种增加归因于在辐照期间进行的修复。在修复缺陷菌株大肠杆菌Bs-1和Csyn-中作用较小，在细胞外状态下不能进行修复的噬菌体T1和T4中不存在。在这些实验中，可用于修复的延长时间只占存活增加的很小一部分。显然，主要因素是任何时候出现的病变数量仍然相对较低。假定完全修复，而不仅仅是切除步骤，可以在缓冲期间发生。这种解释得到了实验的支持，在实验中，细胞暴露于高分级照射和单剂量照射的组合。修复过程中的相互干扰，可能是由于互补DNA链中修复区域的重叠，如果存在许多损伤，可能会大大降低修复效率。这解释了B/r和其他大肠杆菌菌株的“肩扛”生存曲线是由于随着紫外线剂量的增加，修复效率降低。
Exposure of E. coli B/r and B at low average dose rates of UV radiation (2537 A) produced either by fractionated doses or by continuous irradiation at a very low dose rate (80 ergs/mm2/hr.) results in much increased survival compared to single exposure at high dose rate. This increase is attributed to repair taking place during the irradiation period. The effect is small in the repair-deficient strains E. coli Bs-1 and Csyn- and is absent in phage T1 and T4, which cannot undergo repair in the extracellular state. The prolonged time available for repair in these experiments accounts for only a very minor part of the increase in survival. The principal factor apparently is that the number of lesions present at any time remains relatively low. Presumable complete repair, not only the excision step, can occur in buffer during the irradiation period. This interpretation is supported by experiments in which cells were exposed to combinations of highly fractionated irradiation and single-dose irradiation. Mutual interference in repair, possibly by overlapping of repair regions in complementary DNA strands, probably reduces considerably the repair efficiency if many lesions are present. This explains the "shouldered" survival curves of B/r and possibly other E. coli strains as due to decreasing repair efficiency with increasing UV dose.