Nieto J M, Bailey M J, Hughes C, Koronakis V
Department of Pathology, University of Cambridge, UK.
Mol Microbiol. 1996 Feb;19(4):705-13. doi: 10.1046/j.1365-2958.1996.446951.x.
Expression of the Escherichia coli hlyCABD operon encoding synthesis, maturation and export of haemolysin toxin was strongly dependent upon a 35 bp DNA sequence, spanning the element GGCGGTAG, located 2 kbp upstream. When the hly operon was placed under the control of the inducible tac promoter, expression remained dependent upon this element, when transcribed in its native orientation 3' of the promoter. The increase in ptac-directed transcription was strongest for the distal, export genes of the hly operon, and was particularly striking when ptac and the element were placed far upstream. The element did not influence transcript stability, and we suggest that it is a key component of a novel regulatory mechanism may suppresses transcription polarity within operons. The mechanism that be of widespread importance in bacterial gene expression because the 8 bp element is present in many Gram-negative species as an upstream component of operons encoding the production of toxins and the surface assembly of polysaccharides and components required for the conjugal transfer of DNA. We name it the ops element for operon polarity suppressor.
编码溶血素毒素合成、成熟和输出的大肠杆菌hlyCABD操纵子的表达强烈依赖于一个35 bp的DNA序列，该序列跨越位于上游2 kbp处的GGCGGTAG元件。当hly操纵子置于可诱导的tac启动子控制下时，在启动子3'端以其天然方向转录时，表达仍依赖于该元件。对于hly操纵子的远端输出基因，ptac指导的转录增加最为显著，当ptac和该元件置于 far upstream时尤其明显。该元件不影响转录本稳定性，我们认为它是一种新型调控机制的关键组成部分，该机制可能抑制操纵子内的转录极性。这种机制在细菌基因表达中可能具有广泛的重要性，因为8 bp元件在许多革兰氏阴性菌中作为操纵子的上游成分存在，这些操纵子编码毒素的产生、多糖的表面组装以及DNA接合转移所需的成分。我们将其命名为操纵子极性抑制元件（ops元件）。
