Lee H S, Ishihama A, Kustu S
Department of Plant Pathology, University of California, Berkeley 94720.
J Bacteriol. 1993 Apr;175(8):2479-82. doi: 10.1128/jb.175.8.2479-2482.1993.
Several activators of sigma 70 holoenzyme whose binding sites lie upstream of the -35 region of promoters require the C-terminal region of the alpha subunit of RNA polymerase to activate transcription. (These are among class I activators, which require the C-terminal region of the alpha subunit for transcription activation.) Because transcription by sigma 54 holoenzyme universally depends upon activators whose binding sites lie well upstream (or downstream) of promoters, we determined whether the C-terminal region of the alpha subunit was also required for transcription from the sigma 54-dependent promoter for the glnA operon. Nitrogen regulatory protein C-dependent activation from the glnA promoter remained good when RNA polymerases containing C-terminal truncations of the alpha subunit were employed. This was also the case for nitrogen fixation protein A-dependent activation if a nitrogen fixation protein A-binding site was appropriately placed upstream of the glnA promoter. These results lead to the working hypothesis (as yet untested) that activators of sigma 54 holoenzyme, which appear to make direct physical contact with the polymerase to catalyze a change in its conformation, activate the sigma 54 holoenzyme by contacting the sigma subunit rather than the alpha subunit of the core enzyme.
几种σ70全酶激活剂，其结合位点位于启动子-35区上游，需要RNA聚合酶α亚基的C末端区域来激活转录。（这些属于I类激活剂，它们需要α亚基的C末端区域来激活转录。）由于σ54全酶的转录普遍依赖于结合位点位于启动子上游（或下游）较远位置的激活剂，我们确定了α亚基的C末端区域对于谷氨酰胺合成酶操纵子的σ54依赖型启动子的转录是否也是必需的。当使用含有α亚基C末端截短的RNA聚合酶时，谷氨酰胺合成酶启动子依赖氮调节蛋白C的激活作用仍然良好。如果在谷氨酰胺合成酶启动子上游适当位置放置一个固氮蛋白A结合位点，那么依赖固氮蛋白A的激活作用也是如此。这些结果得出一个尚未得到验证的工作假设：σ54全酶激活剂似乎与聚合酶直接进行物理接触以催化其构象变化，它们通过与核心酶的σ亚基而非α亚基接触来激活σ54全酶。
