Fornace A J
Nature. 1983;304(5926):552-4. doi: 10.1038/304552a0.
The mechanism by which mammalian cells replicate DNA containing pyrimidine dimers is poorly understood. When DNA synthesis is initiated after UV-irradiation in bacteria, parental DNA containing pyrimidine dimers has been shown to 'exchange' into the daughter strand DNA by a recA-dependent mechanism. In earlier experiments, when growing mammalian cells were UV-irradiated and then incubated with labelled thymidine, pyrimidine dimers were initially interpreted to be in the newly synthesized DNA, but later were found to be only adjacent to newly synthesized DNA in daughter strand present before UV treatment. A way to avoid these problems of interpretation would be to use cells in G0 or G1 which are not synthesizing DNA at the time of irradiation. UV damage could then be detected in a very sensitive quantitative assay such as that recently described using alkaline elution and an endonuclease preparation from Micrococcus luteus. I have now used this approach and report that up to 3 dimers per 10(9) daltons of daughter strand DNA could be detected 34-45 h after UV-irradiation in human peripheral blood lymphocytes (PBL), normal human fibroblasts, group A xeroderma pigmentosum (XP) fibroblasts and mouse 3T3 cells. This represents approximately 1-3% of the dimers present in the parent strand at this time after UV.
哺乳动物细胞复制含有嘧啶二聚体的DNA的机制目前还知之甚少。在细菌中，紫外线照射后启动DNA合成时，已证明含有嘧啶二聚体的亲本DNA会通过一种recA依赖机制“交换”到子链DNA中。在早期实验中，当生长中的哺乳动物细胞受到紫外线照射，然后与标记的胸腺嘧啶一起孵育时，嘧啶二聚体最初被认为存在于新合成的DNA中，但后来发现它们仅与紫外线处理前存在的子链中新合成的DNA相邻。避免这些解释问题的一种方法是使用处于G0或G1期的细胞，这些细胞在照射时不进行DNA合成。然后可以在一种非常灵敏的定量检测中检测紫外线损伤，例如最近描述的使用碱性洗脱和来自藤黄微球菌的核酸内切酶制剂的检测方法。我现在采用了这种方法，并报告说，在紫外线照射后34 - 45小时，在人外周血淋巴细胞（PBL）、正常人成纤维细胞、A组着色性干皮病（XP）成纤维细胞和小鼠3T3细胞中，每10(9)道尔顿子链DNA中最多可检测到3个二聚体。这大约占紫外线照射后此时亲本链中二聚体的1 - 3%。
