Promoters for Chlamydia Type III Secretion Genes Show a Differential Response to DNA Supercoiling That Correlates with Temporal Expression Pattern
Promoters for Chlamydia Type III Secretion Genes Show a Differential Response to DNA Supercoiling That Correlates with Temporal Expression Pattern
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DOI：
10.1128/jb.00068-10
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发表时间：
2010-05-15
影响因子：
3.2
通讯作者：
Tan, Ming
中科院分区：
文献类型：
--
作者：
Case, Elizabeth Di Russo;Peterson, Ellena M.;Tan, Ming
III型分泌（T3S）对于衣原体感染的建立和维持是重要的。编码衣原体T3S组分的基因被转录为单独的时间类，但调节其表达时间的机制尚不清楚。在这项研究中，我们证明了10个预测的T3S转录单位的启动子在体外分别由衣原体RNA聚合酶的主要形式转录，而不是由含有sigma的RNA聚合酶的替代形式转录（28）。由于衣原体发育过程中DNA超螺旋的变化已被提出作为时间基因调控的机制，我们研究了T3S启动子对超螺旋密度改变的体外反应。在中期上调的三个T3S基因的启动子响应于增加的DNA超螺旋而被激活。相比之下，三个晚期T3S基因的启动子对超螺旋密度的变化不敏感。这种对DNA拓扑结构变化的差异反应与已报道的与T3S系统无关的代表性中晚期衣原体基因的模式相似。基于这些结果，我们提出衣原体T3S基因的时间表达是由发育周期中调节sigma（66）依赖性基因表达的一般机制控制的。我们的研究结果是一致的模型，其中T3S基因在中期周期上调与其他中期基因一起激活，以响应增加的DNA超螺旋。
Type III secretion (T3S) is important for the establishment and maintenance of a chlamydial infection. The genes encoding T3S components in Chlamydia are transcribed as separate temporal classes, but the mechanisms that regulate the timing of their expression are not understood. In this study, we demonstrate that promoters for 10 predicted T3S transcriptional units are each transcribed in vitro by the major form of chlamydial RNA polymerase but not by an alternative form of RNA polymerase containing sigma(28). Since changes in DNA supercoiling during chlamydial development have been proposed as a mechanism for temporal gene regulation, we examined the in vitro response of T3S promoters to altered superhelical density. Promoters for three T3S genes that are upregulated at mid times were activated in response to increased DNA supercoiling. In contrast, promoters for three late T3S genes were not sensitive to changes in superhelical density. This differential response to changes in DNA topology is similar to the pattern that has been reported for representative mid and late chlamydial genes that are unrelated to the T3S system. Based on these results, we propose that the temporal expression of T3S genes in Chlamydia is controlled by general mechanisms that regulate sigma(66)-dependent gene expression during the developmental cycle. Our results are consistent with a model in which T3S genes that are upregulated in mid cycle are activated together with other mid genes in response to increased DNA supercoiling.