Feng Xiuhong, Walthers Don, Oropeza Ricardo, Kenney Linda J
Department of Microbiology and Immunology, University of Illinois at Chicago, 835 S. Wolcott Avenue, M/C 790, Chicago, IL 60612, USA.
Mol Microbiol. 2004 Nov;54(3):823-35. doi: 10.1111/j.1365-2958.2004.04317.x.
OmpR activates expression of the two-component regulatory system located on Salmonella pathogenicity island 2 (SPI-2) that controls the expression of a type III secretion system, as well as many other genes required for systemic infection in mice. Measurements of SsrA and SsrB protein levels under different growth conditions indicate that expression of these two components is uncoupled, i.e. SsrB is produced in the absence of ssrA and vice versa. This result was suggested from our previous studies, in which two promoters at ssrA/B were identified. The isolated C-terminus of SsrB binds to DNA and protects regions upstream of ssrA, ssrB and srfH from DNase I digestion. Furthermore, the C-terminus of SsrB alone is capable of activating transcription in the absence of the N-terminus. Results from beta-galactosidase assays indicate that the N-terminal phosphorylation domain inhibits the C-terminal effector domain. A previous study from our laboratory reported that ssrA-lacZ and ssrB-lacZ transcriptional fusions were substantially reduced in an ssrB null strain. Results from DNase I protection assays provide direct evidence that SsrB binds at ssrA and ssrB, although the binding sites lie within the transcribed regions. Additional regulators clearly affect gene expression at this important locus, and here we provide evidence that SlyA, a transcription factor that contributes to Salmonella virulence, also affects ssrA/B gene expression.
OmpR激活位于沙门氏菌致病岛2(SPI-2)上的双组分调节系统的表达,该系统控制III型分泌系统以及小鼠全身感染所需的许多其他基因的表达。在不同生长条件下对SsrA和SsrB蛋白水平的测量表明,这两个组分的表达是解偶联的,即SsrB在没有ssrA的情况下产生,反之亦然。这个结果是从我们之前的研究中得出的,在该研究中鉴定了ssrA/B处的两个启动子。分离出的SsrB的C末端与DNA结合,并保护ssrA、ssrB和srfH上游区域免受DNase I消化。此外,单独的SsrB的C末端在没有N末端的情况下能够激活转录。β-半乳糖苷酶分析结果表明,N末端磷酸化结构域抑制C末端效应结构域。我们实验室之前的一项研究报告称,在ssrB缺失菌株中,ssrA-lacZ和ssrB-lacZ转录融合显著减少。DNase I保护分析结果提供了直接证据,表明SsrB结合在ssrA和ssrB处,尽管结合位点位于转录区域内。其他调节因子显然会影响这个重要位点的基因表达,在这里我们提供证据表明,有助于沙门氏菌毒力的转录因子SlyA也会影响ssrA/B基因的表达。