Aki T, Adhya S
Division of Basic Sciences, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4255, USA.
EMBO J. 1997 Jun 16;16(12):3666-74. doi: 10.1093/emboj/16.12.3666.
Transcription from two overlapping gal promoters is repressed by Gal repressor binding to bipartite gal operators, O(E) and O(I), which flank the promoters. Concurrent repression of the gal promoters also requires the bacterial histone-like protein HU which acts as a co-factor. Footprinting experiments using iron-EDTA-coupled HU show that HU binding to gal DNA is orientation specific and is specifically dependent upon binding of GalR to both O(E) and O(I). We propose that HU, in concert with GalR, forms a specific nucleoprotein higher order complex containing a DNA loop. This way, HU deforms the promoter to make the latter inactive for transcription initiation while remaining sensitive to inducer. The example of gal repression provides a model for studying how a 'condensed' DNA becomes available for transcription.
两个重叠的半乳糖启动子的转录受到半乳糖阻遏物的抑制，该阻遏物与位于启动子两侧的双分型半乳糖操纵子O(E)和O(I)结合。半乳糖启动子的同时抑制还需要细菌类组蛋白HU作为辅助因子。使用铁-EDTA偶联的HU进行的足迹实验表明，HU与半乳糖DNA的结合具有方向特异性，并且特别依赖于GalR与O(E)和O(I)两者的结合。我们提出，HU与GalR协同作用，形成一种包含DNA环的特定核蛋白高阶复合物。通过这种方式，HU使启动子变形，使其对转录起始无活性，同时保持对诱导剂的敏感性。半乳糖抑制的例子为研究“浓缩”的DNA如何用于转录提供了一个模型。
