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首页> 外文期刊>Microbial Pathogenesis >Histone-like nucleoid-structuring protein represses transcription of the ehx operon carried by locus of enterocyte effacement-negative Shiga toxin-expressing Escherichia coli
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Histone-like nucleoid-structuring protein represses transcription of the ehx operon carried by locus of enterocyte effacement-negative Shiga toxin-expressing Escherichia coli

机译：组蛋白样核苷结构蛋白抑制肠上皮细胞表达阴性志贺毒素表达大肠杆菌所携带的ehx操纵子的转录

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摘要

Shiga toxin-producing Escherichia coli (STEC) are a significant cause of zoonotic foodborne diarrheal disease in industrialized nations. In addition to Shiga toxin most STEC produce the enterohemolysin (EhxA) toxin. The EhxA toxin is encoded by the ehxCABD operon located on the large plasmid carried by STEC, yet its role in pathogenesis is unknown. A histone-like nucleoid-structuring protein (H-NS) null mutant of STEC O91:H21 strain B2F1 displayed a hyper-hemolytic phenotype, was defective in binding to human colonic epithelial cells, and was non-motile. We concluded that H-NS modulated expression of several genes in B2F1 including the ehx operon. Electrophoretic mobility shift assays indicate that H-NS binds to an 88 bp region of DNA upstream of the ehxC start codon. To determine if the same region of DNA was sensitive to repression by H-NS, a transcriptional fusion was constructed between the putative promoter region of ehx and a promoterless lacZ gene. The beta-galactosidase activity detected was low in E. coli that produced H-NS but was significantly higher in the H-NS null background. Taken together, the data indicates that in STEC the 88 bp region upstream of the ehx operon contains a cis-acting element to which H-NS binds and negatively regulates expression of enterohemolysin.
机译：产生志贺毒素的大肠杆菌（STEC）是工业化国家中人畜共患性食源性腹泻病的重要原因。除志贺毒素外，大多数STEC还会产生肠溶血素（EhxA）毒素。 EhxA毒素由位于STEC携带的大质粒上的ehxCABD操纵子编码，但在发病机理中的作用尚不清楚。 STEC O91：H21菌株B2F1的组蛋白样核苷酸样结构蛋白（H-NS）无效突变体表现出超溶血性表型，与人结肠上皮细胞的结合存在缺陷，并且不能运动。我们得出的结论是，H-NS调节了包括ehx操纵子在内的B2F1中几个基因的表达。电泳迁移率变动分析表明，H-NS与ehxC起始密码子上游DNA的88 bp区域结合。为了确定同一区域的DNA是否对H-NS抑制敏感，在ehx的假定启动子区域和无启动子lacZ基因之间构建了转录融合。在产生H-NS的大肠杆菌中检测到的β-半乳糖苷酶活性较低，但在H-NS无效背景下则明显较高。两者合计，数据表明，在STEC中，ehx操纵子上游88 bp的区域包含一个顺式作用元件，H-NS与该顺式作用元件结合，并负调节肠溶血素的表达。

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