Witkin E M
Proc Natl Acad Sci U S A. 1974 May;71(5):1930-4. doi: 10.1073/pnas.71.5.1930.
Inhibition of DNA replication in E. coli results in coordinate expression of a cluster of diverse functions, including prophage induction and filamentous growth, many of which are thermally inducible, without inhibition of DNA synthesis, in strains carrying a mutation in the "tif" locus. It has been proposed that one of the inducible functions in this cluster is responsible for the ultraviolet mutability of E. coli. As a test of this hypothesis, the effect of postirradiation temperature elevation on ultraviolet mutability was compared in strains differing by a tif mutation. In a tif(+) strain, raising the temperature to 42 degrees after irradiation did not change the frequency of induced mutations to tryptophan-independence. Similar treatment of a tif-1 strain resulted in as much as a 10-fold increase in the induced mutation yield. Thermal enhancement of ultraviolet mutability in the tif-1 strain was prevented or promoted by agents known to exert parallel effects on thermal induction of lambda prophage in tif lysogens. The results support the hypothesis that ultraviolet mutability in E. coli depends upon an inducible function that is normally expressed only when DNA replication is inhibited.
大肠杆菌中DNA复制的抑制会导致多种不同功能的协同表达，包括原噬菌体诱导和丝状生长，其中许多功能在携带“tif”位点突变的菌株中是热诱导型的，且不依赖于DNA合成。有人提出，该簇中一种可诱导功能与大肠杆菌的紫外线诱变作用有关。作为对这一假设的检验，我们比较了经紫外线照射后温度升高对不同tif突变菌株紫外线诱变作用的影响。在tif(+)菌株中，照射后将温度升至42摄氏度不会改变诱导产生色氨酸非依赖型突变的频率。对tif-1菌株进行类似处理后，诱导突变率增加了多达10倍。已知对tif溶原菌中λ原噬菌体热诱导具有类似作用的试剂，可抑制或促进tif-1菌株中紫外线诱变的热增强效应。这些结果支持了这样一种假设，即大肠杆菌中的紫外线诱变作用取决于一种通常仅在DNA复制受到抑制时才表达的可诱导功能。
