Richter-Dahlfors A A, Andersson D I
Department of Microbiology, Uppsala University, Sweden.
Mol Microbiol. 1992 Mar;6(6):743-9. doi: 10.1111/j.1365-2958.1992.tb01524.x.
Expression of the Cob operon in Salmonella typhimurium is repressed by cobalamin (Cbl). Here it is shown that Cbl repression is mediated by a post-transcriptional regulatory mechanism that requires sequences within the leader and the first translated open reading frame, the cbiA gene. Transcriptional and translational Cob::lacZ fusions containing various lengths of Cob DNA were analysed. In a translational Cob::lacZ fusion 407 bp of leader sequence (+69 to +476) was sufficient to confer normal repression. However in a transcriptional Cob::lacZ fusion a 618 bp region (+69 to +687) was required for normal repression. This 618 bp region included sequences in the leader as well as sequences within the cbiA gene. Point mutations which resulted in loss of repression control were isolated and shown to be clustered in the leader sequence (+257 to +380). This region contains a putative hairpin-loop structure which we propose functions as an RNA operator site for a vitamin B12-responsive repressor protein.
鼠伤寒沙门氏菌中钴胺素操纵子（Cob operon）的表达受钴胺素（Cbl）抑制。本文表明，Cbl抑制是由一种转录后调控机制介导的，该机制需要前导序列和第一个翻译的开放阅读框cbiA基因中的序列。分析了含有不同长度Cob DNA的转录和翻译Cob::lacZ融合体。在翻译的Cob::lacZ融合体中，407 bp的前导序列（+69至+476）足以赋予正常抑制作用。然而，在转录的Cob::lacZ融合体中，正常抑制需要一个618 bp的区域（+69至+687）。这个618 bp的区域包括前导序列中的序列以及cbiA基因中的序列。分离出导致抑制控制丧失的点突变，并显示其聚集在前导序列（+257至+380）中。该区域包含一个推定的发夹环结构，我们认为它作为维生素B12反应性阻遏蛋白的RNA操纵位点发挥作用。
