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首页> 外文期刊>Infection and immunity >Regulation of the Overlapping pic/set Locus in Shigella flexneri and Enteroaggregative Escherichia coli
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Regulation of the Overlapping pic/set Locus in Shigella flexneri and Enteroaggregative Escherichia coli

机译：弗氏志贺氏菌和肠聚合性大肠杆菌中重叠的pic / set基因座的调控

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摘要

Most strains of Shigella flexneri 2a and enteroaggregative Escherichia coli carry a highly conserved chromosomal locus which encodes a 109-kDa secreted mucinase (called Pic) and, on the opposite strand in overlapping fashion, an oligomeric enterotoxin called ShET1, encoded by the setA and setB genes. Here, we characterize the genetic regulation of these overlapping genes. Our data suggest that pic and the setBA loci are transcribed as complementary 4-kb mRNA species. The major pic promoter is maximally activated at 37°C in exponential growth phase. Our data suggest that the setB gene is transcribed from a promoter which lies more than 1.5 kb upstream of the setB structural gene; setA may be transcribed via readthrough of the setB transcript and possibly by its own promoter. The long leader of the setB gene provides a strong silencing effect on setB transcription. The signals which provide relief from setB silencing are not clear, but significant induction is observed in a continuous anaerobic culture of human fecal bacteria, suggesting that some complex characteristics of the human intestine act to lift repression of setB expression. Our studies provide the first insights into the mechanisms affecting expression of this unusual virulence locus.
机译：大部分志贺氏菌 2a和肠聚集性大肠杆菌菌株携带高度保守的染色体基因座，该基因座编码109-kDa分泌的粘蛋白酶（称为Pic），并且在重叠的相反链上一种叫做ShET1的低聚肠毒素，由 setA 和 setB 基因编码。在这里，我们表征了这些重叠基因的遗传调控。我们的数据表明 pic 和 setBA 基因座被转录为互补的4kb mRNA物种。主要的 pic 启动子在指数生长期在37°C时最大程度地被激活。我们的数据表明， setB 基因是从位于 setB 结构基因上游1.5 kb以上的启动子转录而来的。 setA 可以通过 setB 转录本的通读转录，也可以通过其自身的启动子转录。 setB 基因的长前导序列对 setB 转录具有很强的沉默作用。消除 setB 沉默的信号尚不清楚，但是在人类粪便细菌的连续厌氧培养中观察到了明显的诱导作用，这表明人类肠道的某些复杂特征起到了解除抑制的作用。 > setB 表达式。我们的研究为影响这种异常毒力基因座表达的机制提供了第一见解。

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