乳糖阻遏物与携带两个间隔适当的乳糖操纵基因的线性DNA形成环。

lac repressor forms loops with linear DNA carrying two suitably spaced lac operators.

作者信息

Krämer H, Niemöller M, Amouyal M, Revet B, von Wilcken-Bergmann B, Müller-Hill B

出版信息

EMBO J. 1987 May;6(5):1481-91. doi: 10.1002/j.1460-2075.1987.tb02390.x.

Tetrameric lac repressor may bind to two lac operators on one DNA fragment and induce the intervening DNA to form a loop. Electron microscopy, non-denaturing polyacrylamide gel electrophoresis, and DNase I protection experiments were used to demonstrate such DNA loops, where the distance between the centres of symmetry of the two lac operators varies between 63 and 535 bp. Formation of a DNA loop is favoured by correct phasing of the two lac operators and a low concentration of both components of the reaction. When a large excess of lac repressor over DNA is used, a 'tandem' structure is observed, in which both lac operators are occupied independently by two repressor tetramers. When the concentrations of both lac repressor and lac operator are high, a 'sandwich' structure is observed, in which two DNA molecules are connected by two lac repressor tetramers in trans.

四聚体乳糖阻遏物可结合在一个DNA片段上的两个乳糖操纵基因，并诱导中间的DNA形成一个环。电子显微镜、非变性聚丙烯酰胺凝胶电泳和DNase I保护实验被用于证明这种DNA环，其中两个乳糖操纵基因的对称中心之间的距离在63至535碱基对之间变化。两个乳糖操纵基因的正确相位和反应中两种成分的低浓度有利于DNA环的形成。当使用相对于DNA大量过量的乳糖阻遏物时，会观察到一种“串联”结构，其中两个乳糖操纵基因均被两个阻遏物四聚体独立占据。当乳糖阻遏物和乳糖操纵基因的浓度都很高时，会观察到一种“三明治”结构，其中两个DNA分子通过两个反式的乳糖阻遏物四聚体相连。