Relationship between regulation of cholera toxin production by lysophosholipase and ToxR.

通过脉冲场电泳和Southern杂交，发现霍乱弧菌染色体上的lypA带toxR基因位于同一条NotI DNA片段上。利用含有lypA基因内部片段的自杀载体构建了lypA基因的插入突变体。这些插入突变株的产毒能力降低，特别是在产毒能力强的菌株中，如569B株，产毒能力降低的菌株中，toxR基因的转录水平也降低。在该缺失突变体中，霍乱毒素的产生和toxR的转录没有明显降低。这表明质粒插入突变体中的lypA可能会影响邻近基因，从而影响霍乱毒素的产生。

By pulse-field electrophoresis and Southern hybridization, we found the lypA band toxR geneswere in the same NotI DNA fragment of Vibrio cholerae chromosome. This suggest close proximity between lypA and toxR.Insertional mutants in the lypA gene was constructed using suicide vector containing inner fragment of the lypA gene. Cholera toxin-producing ability was reduced in these insertional mutants, especially in the strain which highly produces the toxin, such as strain 569B.In the insertional mutant strain which reduced production of cholera toxin, transcription of toxR was also down-regulated.We deleted the lypA gene completely by double-crossover recombination. In this deletion mutant, production of cholera toxin and transcription of toxR were not reduced clearly. This suggest that insertion of plasmid into the lypA in the insertional mutant may affect the neighboring genes, which affect production of cholera toxin.