Lin P F, Howard-Flanders P
Mol Gen Genet. 1976 Jul 23;146(2):107-15. doi: 10.1007/BF00268079.
Genetic recombination induced by structural damage in DNA molecules was investigated in E. coli K12 (lambda) lysogens infected with genetically marked phage lambda. Photoproducts were induced in the phage DNA before infection by exposing them either to 313 nm light in the presence of acetophenone or to 254 nm light. To test the role of the replication of the damaged phage DNA on the frequency of the induced recombination, both heteroimmune and homimmune crosses were performed. First, samples of a heteroimmune phage lambda imm434 P80 exposed to these treatments were allowed to infect cells lysogenic for prophage lambda cI857 P3. Phage DNA replication and maturation took place, and the resulting progeny phages were assayed for the frequency of P+ recombinants. Recombination was less frequent in infected cells exposed to visible light and in wild type cells able to perform excision repair than in excision-defective lysogens. Therefore, much of the induced recombination can be attributed to the pyrimidine dimers in the phage DNA, the only photoproducts known to be dissociated by photoreactivating enzyme. Second, in homoimmune crosses, samples of similarly treated homoimmune lambda P3 phages were allowed to infect lysogens carrying lambda cI857 P80. Replication of the phage DNA containing ultraviolet photoproducts was repressed by lambda immunity, and was further blocked by the lack of the P gene product needed for replication. The lysogens were purified and scored for both colony forming ability and for P+ recombinant prophages. The 254 nm photoproducts increased the frequency of recombination in these homimmune crosses, even though phage DNA replication was blocked. Irradiation with 313 nm light and acetophenone M, which produces dimers and unknown photoproducts, was not as effective per dimer as the 254 nm light. It is concluded from these results that certain unidentified 254 nm photoproducts can cause recombination even in the absence of DNA replication. They are not pyrimidine dimers, as they are not susceptible to excision repair or photoreactivation. In contrast, pyrimidine dimers appear to cause recombination only when the DNA containing them undergoes replication.
在感染了基因标记噬菌体λ的大肠杆菌K12（λ）溶原菌中，研究了DNA分子结构损伤诱导的基因重组。在感染前，通过将噬菌体DNA暴露于苯乙酮存在下的313nm光或254nm光来诱导光产物。为了测试受损噬菌体DNA复制对诱导重组频率的作用，进行了异源免疫和同源免疫杂交。首先，将暴露于这些处理的异源免疫噬菌体λ imm434 P80的样本用于感染携带原噬菌体λ cI857 P3的溶原菌细胞。噬菌体DNA复制和成熟发生，然后测定所得子代噬菌体中P+重组体的频率。与能够进行切除修复的野生型细胞相比，暴露于可见光的感染细胞和切除缺陷型溶原菌中的重组频率较低。因此，大部分诱导重组可归因于噬菌体DNA中的嘧啶二聚体，这是已知可被光复活酶解离的唯一光产物。其次，在同源免疫杂交中，将经过类似处理的同源免疫λ P3噬菌体样本用于感染携带λ cI857 P80的溶原菌。含有紫外线光产物的噬菌体DNA的复制受到λ免疫的抑制，并且由于缺乏复制所需的P基因产物而进一步受阻。纯化溶原菌，并对其菌落形成能力和P+重组原噬菌体进行评分。254nm光产物增加了这些同源免疫杂交中的重组频率，即使噬菌体DNA复制被阻断。用313nm光和苯乙酮M照射产生二聚体和未知光产物，每二聚体的效果不如254nm光。从这些结果可以得出结论，某些未鉴定的254nm光产物即使在没有DNA复制的情况下也能引起重组。它们不是嘧啶二聚体，因为它们不易受到切除修复或光复活的影响。相比之下，嘧啶二聚体似乎仅在含有它们的DNA进行复制时才会引起重组。
