Role of nucleoid-associated proteins Hha and H-NS in expression of Salmonella enterica activators HilD, HilC, and RtsA required for cell invasion
Role of nucleoid-associated proteins Hha and H-NS in expression of Salmonella enterica activators HilD, HilC, and RtsA required for cell invasion
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DOI：
10.1128/jb.00905-07
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发表时间：
2007-10-01
影响因子：
3.2
通讯作者：
Kadner, Robert J.
中科院分区：
文献类型：
--
作者：
Ekhnovich, Igor N.;Kadner, Robert J.
沙门氏菌致病岛1上沙门氏菌入侵基因的协调表达受涉及AraC/XylS家族转录激活因子HilD、HilC和RtsA以及核相关蛋白的复杂调控回路的控制。单拷贝转录融合用于评估类核蛋白Hha和H-NS对hilD、hilC和rtsA表达的影响。数据显示，所有三个基因hilD、hilC和rtsA均被H-NS和/或Hha抑制。在所检测的基因中，rtsA的阻遏作用最强。在hns和hha突变体中rtsA-lac的水平同样升高，并且在低渗透压条件下在hns hha双突变体中进一步增强。电泳迁移率变动实验表明，H-NS和Hha直接结合到rtsA启动子。除了在低渗透压条件下由H-NS/Hha施加的阴性对照之外，同源毒力激活物HilD、MIC和RtsA（Hil激活物）在高盐培养基中诱导rtsA-lac表达。rtsA启动子的DNA酶足迹分析揭示了所有三种Hil激活剂的一个共同DNA结合位点，该位点集中在相对于转录起始位点的-54位。然而，在没有Hha和H-NS的情况下，rtsA启动子的HIL调节丧失，并且rtsA转录不需要Hil激活剂。这些结果一起表明，HilD，HilC，和RtsA蛋白诱导的rtsA启动子的转录通过抵消H-NS/Hha介导的抑制。
The coordinate expression of Salmonella enterica invasion genes on Salmonella pathogenicity island 1 is under the control of the complex circuits of regulation that involve the AraC/XylS family transcriptional activators HilD, HilC, and RtsA and nucleoid-associated proteins. Single-copy transcription fusions were used to assess the effects of nucleoid-associated proteins Hha and H-NS on hilD, hilC, and rtsA expression. The data show that all three genes, hilD, hilC, and rtsA, were repressed by H-NS and/or Hha. The repression of rtsA was the highest among tested genes. The level of rtsA-lac was equally elevated in hns and hha mutants and was further enhanced in the hns hha double mutant under low-osmolarity conditions. Electrophoretic mobility shift experiments showed that H-NS and Hha directly bind to the rtsA promoter. In addition to the negative control that was exerted by H-NS/Hha under low-osmolarity conditions, the homologous virulence activators HilD, MIC, and RtsA (Hil activators) induced rtsA-lac expression in a high-salt medium. A DNase footprinting assay of the rtsA promoter revealed one common DNA-binding site for all three Hil activators centered at position -54 relative to the transcriptional start site. In the absence of Hha and H-NS, however, osmoregulation of the rtsA promoter was lost, and Hil activators were not required for rtsA transcription. These results taken together suggest that the HilD, HilC, and RtsA proteins induce the transcription of the rtsA promoter by counteracting H-NS/Hha-mediated repression.