Katayama S, Ninomiya M, Minami J, Okabe A, Hayashi H
Department of Microbiology, Kagawa Medical School.
Microbiol Immunol. 1990;34(1):11-24. doi: 10.1111/j.1348-0421.1990.tb00987.x.
The production of heat-labile enterotoxin (LT) in 76 strains of human enterotoxigenic Escherichia coli (ETEC) varied by a factor of 100. Three ETEC strains that differ in the levels of LT production were chosen for the cloning of LT genes (toxAB) into plasmid pBR322, and the gene structure and expression were compared in E. coli HB101. The recombinant of the low LT-producing strain produced LT at the same level as that of the moderate LT-producing strain, but that of the high-level producer continued to produce at a level 14-21 times higher than the others. The restriction maps of the coding regions of the cloned LT genes (toxAB) were identical, but the flanking regions were dissimilar. The content of LT mRNA per cell, examined by Northern blot analysis, was higher in the high producer than the others by 6 times. The promoter strengths of the recombinants were all alike. LT mRNA of the high producer was more stable than that of the moderate one by 1.3 times, but the difference was not large enough to explain the difference of the content of LT mRNA. It was shown that LT production can be controlled at a transcriptional step, and DNA structure of the flanking regions may be involved in the control of the LT gene expression.
76株产肠毒素大肠杆菌（ETEC）产生不耐热肠毒素（LT）的能力相差100倍。选择3株LT产生水平不同的ETEC菌株，将LT基因（toxAB）克隆到质粒pBR322中，并在大肠杆菌HB101中比较基因结构和表达情况。低LT产生菌株的重组体产生LT的水平与中等LT产生菌株相同，但高产量菌株的重组体产生LT的水平仍比其他菌株高14 - 21倍。克隆的LT基因（toxAB）编码区的限制性图谱相同，但侧翼区不同。通过Northern印迹分析检测，高产菌株每细胞中LT mRNA的含量比其他菌株高6倍。重组体的启动子强度都相似。高产菌株的LT mRNA比中等产量菌株的LT mRNA稳定性高1.3倍，但差异不足以解释LT mRNA含量的差异。结果表明，LT的产生可在转录步骤受到控制，侧翼区的DNA结构可能参与LT基因表达的调控。
