Li Haiping, Granat Anastasiya, Stewart Valley, Gillespie Jerry R
Western Institute for Food Safety and Security, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
FEMS Microbiol Lett. 2008 Aug;285(2):257-62. doi: 10.1111/j.1574-6968.2008.01240.x. Epub 2008 Jul 9.
Escherichia coli hemolysin, also termed alpha-hemolysin, is a virulence factor for extraintestinal E. coli. Hemolysin operon (hlyCABD) transcription is inhibited by the nucleoid-associated protein, H-NS. This inhibition is stronger at lower growth temperature. This study investigated transcription of the homologous EHEC hemolysin (enterohemolysin) operon (ehxCABD) in EHEC O157:H7 strain EDL933. We examined the influence of H-NS, the sigma factor RpoS, and the small RNA DsrA, which is known to inhibit H-NS function and to stimulate RpoS synthesis. During growth at 30 degrees C, DsrA overexpression increased ehxA transcription in the wild type but not in an hns deletion mutant. During growth at 37 degrees C, DsrA overexpression increased ehxA transcription independent of hns genotype. This indicates that DsrA influences ehxCABD operon transcription by two different routes, one (at lower temperature) at least partially dependent on H-NS, and one (at higher temperature) independent of H-NS. An rpoS deletion mutant expressed nondetectable levels of ehxA mRNA regardless of growth temperature or DsrA overexpression, indicating that the RpoS sigma factor is essential for ehxCABD operon expression.
大肠杆菌溶血素，也称为α-溶血素，是肠道外大肠杆菌的一种毒力因子。溶血素操纵子（hlyCABD）的转录受到类核相关蛋白H-NS的抑制。这种抑制在较低生长温度下更强。本研究调查了肠出血性大肠杆菌（EHEC）O157:H7菌株EDL933中同源EHEC溶血素（肠溶血素）操纵子（ehxCABD）的转录情况。我们研究了H-NS、σ因子RpoS以及已知可抑制H-NS功能并刺激RpoS合成的小RNA DsrA的影响。在30℃生长期间，DsrA过表达增加了野生型中ehxA的转录，但在hns缺失突变体中没有增加。在37℃生长期间，DsrA过表达增加了ehxA的转录，且与hns基因型无关。这表明DsrA通过两种不同途径影响ehxCABD操纵子的转录，一种（在较低温度下）至少部分依赖于H-NS，另一种（在较高温度下）不依赖于H-NS。无论生长温度或DsrA过表达如何，rpoS缺失突变体中ehxA mRNA的表达水平均检测不到，这表明RpoS σ因子对于ehxCABD操纵子的表达至关重要。
