CS3纤毛抗原表达调控机理的研究

Studies on the gene expression regulation of the CS3 fimbriaeantigen of enterotoxigenic Escherichia coli

CS3亚基结构基因的核苷酸序列分析表明,在其翻译起始位点的上游存在着rbs位点及原核启动子的—10区和—35区DNA序列。凝胶阻滞和启动报告基因表达的实验确证了CS3亚基结构基因具有自身的启动子(Ps),怛它的作用受其上游区域的抑制。核苷酸序列分析发现,在Ps—35区上游550bp和840bp处各存在一个富A-T簇。结合原核启动子的一般作用规律推知,CS3的表达可能受DNA结合蛋白型的正向调节因子的作用,互补实验结果表明cfaD基因不仅可消除上游区对Ps的抑制,而且可大幅度地提高Ps的启动能力。在分析表达调控的基础上获得CS3重组高效表达。同时提出了其表达调控模型。

According to the nucleotide sequence, the CS3 subunit gene has a typical ribosome binding site(rbs). and -10 as well as -35 sequences of the CS3 promoter upstream from the translation start sue. Based on the results of gel retardation and expression of a reporter gene, the CS3 structural gene was under the control of this promoter, but it could he inhibited by its upstream sequence. Sequence analyses also revealed that there existed two regions of (A-T)-rich sequence. From these results, we inferred that expression of the CS3 gene may be regulated by a DNA-binding protein which is a positive regulator. Complementation analyses showd that the cfa D, a positive regulator of the CFA/1 opreron could not only eliminated the inhibition caused by the upstream region, but also greatly enhanced the expression from the promoter of the CS3 gene. A model for the regulation of CS3 expression was proposed.