細菌RNA聚合酶通過σ因子來達到識別基因的目的，其中很多應激反應基因依賴于σ54因子,，它們能和啟動子DNA結合形成一個穩(wěn)定的封閉復合物,，這對于轉錄過程很重要,。轉錄的開始需要結合于轉錄起始位點上游的激活蛋白驅動的ATP水解。在2008年11月7日出版的《分子細胞》（Molecular Cell）上,，一組來自英國帝國理工學院的科學家提出了形成以上封閉復合物的結構基礎，并分析了激活蛋白啟動轉錄過程的機制,。
轉錄過程的開始需要將一種包含RNA聚合酶（RNA polymerase RNAP）以及雙鏈啟動子DNA的封閉啟動子復合物轉變?yōu)殚_放型復合物,，因為只有發(fā)生這一過程，生物酶才能與單鏈形式的DNA模板發(fā)生作用,。而細菌RNAP和主要的σ因子σ54形成的復合物是封閉型的,，只有通過依賴于ATP水解的激活蛋白重塑作用,，它們才能變?yōu)殚_放復合物。以上重塑作用使DNA解鏈,，促使封閉復合物發(fā)生轉變,。
在本期刊物的封面文章中，Bose等科學家提出了細菌RNAP與σ54結合產生的復合物的冷凍電子顯微鏡的重建結果,，除此之外他們也得到了RNAP-σ54復合物與一個AAA+激活子結合的重建結果,。結合光交聯數據并找到啟動子DNA與這一復合物結合的位點，研究小組解釋了封閉型RNAP-σ54復合物為何無法與DNA模板結合,，此外,，科學家們還提出激活子的結合導致的結構變化是如何形成構象改變的，這最終將導致開放型復合物的形成,。（生物谷Bioon.com）
生物谷推薦原始出處：
Molecular Cell,，Volume 32, Issue 3, 337-346, 7 November 2008，Daniel Bose, Xiaodong Zhang
Organization of an Activator-Bound RNA Polymerase Holoenzyme
Daniel Bose1,4,Tillmann Pape1,4,Patricia C. Burrows2,Mathieu Rappas1,5,Siva R. Wigneshweraraj3,Martin Buck2andXiaodong Zhang1,,
1 Division of Molecular Biosciences, Centre for Structural Biology, Department of Life Sciences, Faculty of Natural Sciences, Imperial College London, London SW7 2AZ, UK
2 Division of Biology, Department of Life Sciences, Faculty of Natural Sciences, Imperial College London, London SW7 2AZ, UK
3 Division of Investigative Science, Department of Microbiology, Faculty of Medicine, Imperial College London, London SW7 2AZ, UK
Transcription initiation involves the conversion from closed promoter complexes, comprising RNA polymerase (RNAP) and double-stranded promoter DNA, to open complexes, in which the enzyme is able to access the DNA template in a single-stranded form. The complex between bacterial RNAP and its major variant sigma factor σ54 remains as a closed complex until ATP hydrolysis-dependent remodeling by activator proteins occurs. This remodeling facilitates DNA melting and allows the transition to the open complex. Here we present cryoelectron microscopy reconstructions of bacterial RNAP in complex with σ54 alone, and of RNAP-σ54 with an AAA+ activator. Together with photo-crosslinking data that establish the location of promoter DNA within the complexes, we explain why the RNAP-σ54 closed complex is unable to access the DNA template and propose how the structural changes induced by activator binding can initiate conformational changes that ultimately result in formation of the open complex.
