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首页> 外文期刊>Journal of Virology >Effects of UV irradiation on the fate of 5-bromodeoxyuridine-substituted bacteriophage T4 DNA.
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Effects of UV irradiation on the fate of 5-bromodeoxyuridine-substituted bacteriophage T4 DNA.

机译：紫外线辐射对5-溴脱氧尿苷取代的噬菌体T4 DNA命运的影响。

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We have carried out a series of experiments designed to characterize the impact of UV irradiation (260 nm) on 5-bromodeoxyuridine-labeled (heavy) T4 bacteriophage, both before and after infection of Escherichia coli. In many respects, these effects differ greatly from those previously described for non-density-labeled (light) phage. Moreover, our results have led us to propose a model for a novel mechanism of host-mediated repair synthesis, in which excision of UV-damaged areas is followed by initiation of replication, strand displacement, and a considerable amount of DNA replication. UV irradiation of 5-bromodeoxyuridine-labeled phage results in single-stranded breaks in a linear, dose-dependent manner (1.3 to 1.5 breaks per genomic strand per lethal hit). This damage does not interfere with injection of the phage genome, but some of the UV-irradiated heavy phage DNA undergoes additional intracellular breakdown (also dose dependent). However, a minority (25%) of the injected parental DNA is protected, maintaining its preinjection size. This protected moiety is associated with a replicative complex of DNA and proteins, and is more efficiently replicated than is the parental DNA not so associated. Most of the progeny DNA is also found with the replicative complex. The 5-bromodeoxyuridine of heavy phage DNA is debrominated by UV irradiation, resulting in uracil which is removed by host uracil glycosylase. Unlike the simple gap-filling repair synthesis after infection with UV-irradiated light phage, the repair replication of UV-irradiated heavy phage is extensive as determined by density shift of the parental label in CsC1 gradients. The newly synthesized segments are covalently attached to the parental fragments. The repair replication takes place even in the presence of chloramphenicol, a protein synthesis inhibitor, suggesting it is host mediated. Furthermore, the extent of the repair replication is greater at higher doses of UV irradiation applied to the heavy phage. This abundant synthesis results ultimately in dispersion of the parental sequences as short stretches in the midst of long segments of newly synthesized progeny DNA. Together, the extensive replication and the resulting distribution pattern of parental sequences, without significant solubilization of parental label, are most consistent with a model of repair synthesis in which the leading strand displaces, rather than ligates to, the encountered 5' end.
机译：我们已经进行了一系列实验，该实验旨在表征UV辐射（260nm）对5-溴脱氧尿苷标记（重）T4噬菌体的影响，两者在感染大肠杆菌之前和之后。在许多方面，这些效果极大地不同于先前针对非密度标记（Light）噬菌体的那些。此外，我们的结果导致我们提出了一种模型，用于宿主介导的修复合成的新机制，其中紫外线损坏区域的切除随后进行复制，链位移和大量的DNA复制。 5-溴脱氧尿苷标记的噬菌体的UV照射导致单链脱落以线性的剂量依赖性方式（每个致死的每个基因组链中的1.3〜1.5断裂）。这种损伤不会干扰噬菌体基因组的注射，但是一些紫外线辐照的重噬菌体DNA经历了额外的细胞内沉积（也依赖于剂量）。然而，保护少数群体（25％）注射的亲本DNA，保护其预注点大小。该受保护部分与DNA和蛋白质的复合复合物相关，并且比不相关的亲本DNA更有效地复制。大多数后代DNA也被复制复合物发现。重噬菌体DNA的5-溴脱氧核嘌呤被UV照射枯燥，导致通过宿主尿嘧啶糖基酶除去的尿嘧啶。与用UV照射光噬菌体感染后的简单间隙填充修复合成不同，UV照射重的重度噬菌体的修复复制是广泛的，如CSC1梯度中亲本标签的密度移位所确定的。新合成的段是共价附着在父母片段上。即使在氯霉素存在下，蛋白质合成抑制剂的存在也会发生修复复制，表明它是宿主介导的。此外，在施加到重型噬菌体的较高剂量的UV照射时，修复复制的程度更大。这种丰富的合成结果最终在新合成的后代DNA的长段中的短延伸中分散治疗序列的分散。在一起，广泛的复制和所得父母序列的产生分布模式，没有父母标签的显着溶解，与修复合成的模型最符合，其中前导链的前导载体而不是连接到遇到的5'端。

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