Bossi L, Smith D M
Cell. 1984 Dec;39(3 Pt 2):643-52. doi: 10.1016/0092-8674(84)90471-9.
We describe two novel types of mutations which decrease transcription of a tRNA operon in Salmonella typhimurium. One mutation consists of a 3 bp deletion at position -70 from the transcription start site. The second mutation is a single bp insertion between the -10 region and the transcription start site. The region around position -70 shows unusual physical properties. DNA fragments carrying the wild-type version of this region exhibit abnormally low electrophoretic mobility in polyacrylamide gels. This anomalous electrophoretic behavior is corrected if gels are run at high temperature or if the fragments contain the 3 bp deletion at -70. Our results indicate the existence of an unusual DNA conformation, probably involving DNA bending, in the region preceding the tRNA operon promoter. This structure is apparently disrupted by the 3 bp deletion. The transcriptional defect of the -70 mutant suggests a role for the unusual conformation in promoter function.
我们描述了两种新型突变，它们会降低鼠伤寒沙门氏菌中一个tRNA操纵子的转录。一种突变是在转录起始位点上游70个碱基对处有一个3个碱基对的缺失。第二种突变是在-10区域与转录起始位点之间有一个单碱基对插入。-70位点周围区域表现出异常的物理特性。携带该区域野生型版本的DNA片段在聚丙烯酰胺凝胶中表现出异常低的电泳迁移率。如果在高温下进行凝胶电泳，或者片段在-70位点处含有3个碱基对的缺失，这种异常的电泳行为就会得到纠正。我们的结果表明，在tRNA操纵子启动子之前的区域存在一种异常的DNA构象，可能涉及DNA弯曲。这种结构显然被3个碱基对的缺失破坏了。-70突变体的转录缺陷表明这种异常构象在启动子功能中起作用。
