Topography of intermediates in transcription initiation of E.coli.
Topography of intermediates in transcription initiation of E.coli.
复制标题
大肠杆菌转录起始中间体的拓扑图。
作者：
P. Schickor;W. Metzger;W. Werel;H. Lederer;H. Heumann
在4 ℃至37 ℃的温度范围内，通过羟基自由基探测大肠杆菌RNA聚合酶T7 A1启动子复合物，产生了三种特征性足迹模式。这些复合体可分为封闭复合体、中间复合体和开放复合体。在封闭复合物中，RNA聚合酶仅在五个螺旋圈的一侧保护DNA。在中间复合体中，保护区的范围进一步向下游延伸两个螺旋圈。DNA螺旋的这个区域被完全保护，表明RNA聚合酶在碱基位置-13和+20之间包裹DNA。在开放复合物中，碱基位置-7和+2之间的一段在中间复合物中被完全保护，变得可以接近羟基自由基，但仅在密码子链中，这表明DNA链是解绕的。我们的数据表明，只有启动子下游的DNA参与这个解旋过程。
Three characteristic footprinting patterns resulted from probing the Escherichia coli RNA polymerase T7 A1 promoter complex by hydroxyl radicals in the temperature range between 4 degrees C and 37 degrees C. These were attributed to the closed complex, the intermediate complex and the open complex. In the closed complex, the RNA polymerase protects the DNA only at one side over five helical turns. In the intermediate complex, the range of the protected area is extended further downstream by two helical turns. This region of the DNA helix is fully protected, indicating that the RNA polymerase wraps around the DNA between base positions −13 and +20. In the open complex, a stretch between base positions −7 and +2, which was fully protected in the intermediate complex, becomes accessible towards hydroxyl radicals but only in the codogenic strand, indicating that the DNA strands are unwound. Our data suggest that only the DNA downstream of the promoter is involved in this unwinding process.