Friden P, Newman T, Freundlich M
Proc Natl Acad Sci U S A. 1982 Oct;79(20):6156-60. doi: 10.1073/pnas.79.20.6156.
The DNA sequence of the promoter-regulatory region of the ilvB operon of Escherichia coli was determined. This region encodes a potential leader polypeptide containing 32 amino acids, 12 of which are the regulatory amino acids valine and leucine. Approximately 50 residues downstream from the coding region for the potential leader peptide is a site for terminating transcription. In vitro transcription experiments show that transcription terminates at this site and produces a leader mRNA of approximately equal to 188 nucleotides. A model for the multivalent regulation of this operon by valyl- and leucyl-tRNA is proposed on the basis of the mutually exclusive formation of five strong stem-and-loop structures in the leader mRNA. In addition, the -35 and -70 regions of this sequence show close structural homologies to areas in cyclic AMP receptor protein (CRP)-dependent promoters reported to be important for CRP function. In vitro transcription from the ilvB promoter was greatly increased by cyclic AMP and CRP. Taken together, these data strongly suggest that the ilvB biosynthetic operon is negatively controlled by multivalent transcription termination and is positively regulated by cyclic AMP and CRP.
测定了大肠杆菌ilvB操纵子启动子调控区的DNA序列。该区域编码一种潜在的前导多肽，含32个氨基酸，其中12个是调控性氨基酸缬氨酸和亮氨酸。在潜在前导肽编码区下游约50个残基处是一个转录终止位点。体外转录实验表明，转录在此位点终止，并产生一个约188个核苷酸的前导mRNA。基于前导mRNA中五个强茎环结构的互斥形成，提出了一种由缬氨酰-tRNA和亮氨酰-tRNA对该操纵子进行多价调控的模型。此外，该序列的-35和-70区域与据报道对环腺苷酸受体蛋白（CRP）功能很重要的CRP依赖性启动子区域显示出紧密的结构同源性。环腺苷酸和CRP极大地增强了ilvB启动子的体外转录。综上所述，这些数据强烈表明，ilvB生物合成操纵子受多价转录终止的负调控，并受环腺苷酸和CRP的正调控。
