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首页> 外文期刊>Infection and immunity >Intracellular Induction of Listeria monocytogenes actA Expression
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Intracellular Induction of Listeria monocytogenes actA Expression

机译：单核细胞增生李斯特菌actA表达的细胞内诱导

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Following entry into the host cytosol, the bacterial pathogen Listeria monocytogenes dramatically increases the expression of several key virulence factors. The expression of actA, whose protein product is required for L. monocytogenes actin-based intracellular motility, is increased by more than 200-fold in cytosolic bacteria in comparison to broth-grown cultures. Two distinct promoter elements have been reported to regulate actA expression. One promoter is located immediately upstream of actA coding sequences, while the second promoter is contributed by the upstream mpl gene via the generation of an mpl-actA-plcB transcript. A series of L. monocytogenes mutants were constructed to define the contributions of individual promoter elements to actA expression. The intracellular induction of actA expression was found to be dependent upon the actA proximal promoter; the mpl promoter appeared to contribute to the extracellular induction of actA but did not affect intracellular levels of expression. The actA promoter is dependent upon a regulatory factor known as PrfA for transcriptional activation; however, no increase in actA expression was detected following the introduction of a high-affinity PrfA binding site within the actA promoter. The presence of a mutationally activated form of PrfA, known as PrfA*, increased overall actA expression in broth-grown cultures of both wild-type and actA promoter mutant strains, but the levels of induction observed were still approximately 50-fold lower than those observed for intracellularly grown L. monocytogenes. Collectively, these results indicate that the dramatic induction of actA expression that occurs in the host cell cytosol is mediated through a single promoter element. Furthermore, intracellular induction of actA appears to require additional steps or factors beyond those necessary for the activation and binding of PrfA to the actA promoter.
机译：进入宿主细胞溶质后，细菌病原体单核细胞增生李斯特菌显着增加了几种关键毒力因子的表达。 actA 的表达，其蛋白质产物是 L 所必需的。与肉汤培养相比，细胞质细菌中基于 monocytogenes 肌动蛋白的细胞内运动性增加了200倍以上。据报道有两个不同的启动子元件调控 actA 表达。一个启动子位于 actA 编码序列的上游，而第二个启动子由上游 mpl 基因通过生成 mpl-actA-plcB < / em>成绩单。一系列 L 。构建单核细胞增生突变体以定义单个启动子元件对 actA 表达的贡献。发现 actA 表达的细胞内诱导依赖于 actA 近端启动子。 mpl 启动子似乎有助于 actA 的细胞外诱导，但不影响细胞内表达水平。 actA 启动子依赖于称为PrfA的调节因子进行转录激活。然而，在 actA 启动子中引入高亲和力的PrfA结合位点后，未检测到 actA 表达的增加。 PrfA的突变激活形式（称为PrfA *）的存在增加了野生型和 actA 启动子突变菌株的肉汤培养物中的整体 actA 表达，但是诱导水平仍比细胞内生长的 L 低约50倍。 单核细胞增生。总的来说，这些结果表明在宿主细胞胞质溶胶中发生的 actA 表达的戏剧性诱导是通过单个启动子元件介导的。此外，细胞内诱导 actA 似乎需要其他步骤或因素，而不是激活和结合PrfA与 actA 启动子所必需的步骤或因素。

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