Franklund C V, Kadner R J
Department of Microbiology, University of Virginia School of Medicine, Charlottesville 22908, USA.
J Bacteriol. 1997 Jun;179(12):4039-42. doi: 10.1128/jb.179.12.4039-4042.1997.
Repression by vitamin B12 of the cobalamin transport protein BtuB in the outer membrane of Escherichia coli operates at both the transcriptional and translational levels and is controlled by transcribed sequences within the leader and proximal portion of the btuB coding sequence. The effects of deletions from either end of this region on repression and expression were determined with lac fusions. An element at the 5' end of the transcript and the putative attenuator within the coding sequence were required for transcriptional repression. The presence of either element caused a marked reduction in btuB-lacZ expression which was reversed by the presence of a conserved sequence element in the leader, suggesting the importance of long-range interactions in the btuB leader for expression and regulation.
维生素B12对大肠杆菌外膜中钴胺素转运蛋白BtuB的抑制作用在转录和翻译水平上均有发生，且受btuB编码序列前导区和近端部分内转录序列的控制。利用lac融合技术确定了该区域两端缺失对抑制作用和表达的影响。转录抑制需要转录本5'端的一个元件和编码序列内的假定衰减子。这两个元件中的任何一个的存在都会导致btuB - lacZ表达显著降低，而前导区中一个保守序列元件的存在可逆转这种降低，这表明btuB前导区中远距离相互作用对表达和调控的重要性。
