Johnson R C, Glasgow A C, Simon M I
Department of Biological Chemistry, University of California, Los Angeles School of Medicine 90024.
Nature. 1987;329(6138):462-5. doi: 10.1038/329462a0.
Site-specific recombination reactions involve the joining or rearrangement of discrete DNA segments in a highly precise manner. A site-specific DNA inversion regulates the expression of flagellin genes in Salmonella by switching the orientation of a promoter. Analysis of the reaction has shown that, in addition to DNA sequences at the two boundaries of the 1-kilobase invertible segment where strand exchange occurs, another cis acting sequence is required for efficient inversion. This 60-base-pair enhancer-like sequence can function at many different locations and in either orientation in a plasmid substrate. It includes two binding sites for a host protein called Factor II or Fis (refs 4 and 5). Here we have investigated the importance of the spatial relationship between the two Fis binding sites for enhancer activity and have found that the correct helical positioning of the binding sites on the DNA is critical. However, this result could not be accounted for by effects on Fis binding. We propose a model for enhancer function in which the enhancer region acts to align the recombination sites into a specific conformation required for productive synapsis.
位点特异性重组反应涉及以高度精确的方式连接或重排离散的DNA片段。一个位点特异性DNA倒位通过切换启动子的方向来调节沙门氏菌中鞭毛蛋白基因的表达。对该反应的分析表明，除了发生链交换的1千碱基可倒位片段的两个边界处的DNA序列外，有效的倒位还需要另一个顺式作用序列。这个60个碱基对的增强子样序列可以在许多不同位置起作用，并且在质粒底物中以任何方向起作用。它包括两个名为因子II或Fis的宿主蛋白的结合位点（参考文献4和5）。在这里，我们研究了两个Fis结合位点之间的空间关系对增强子活性的重要性，发现结合位点在DNA上正确的螺旋定位至关重要。然而，这个结果不能用对Fis结合的影响来解释。我们提出了一个增强子功能模型，其中增强子区域的作用是将重组位点排列成有效突触所需的特定构象。
