Present addresses: Department of Molecular Microbiology & Immunology, L-220 Oregon Health & Science University 3181 SW Sam Jackson Park Road Portland, OR 97239, USA
The response regulator SsrB activates transcription and binds to a region overlapping OmpR binding sites at Salmonella pathogenicity island 2
Article first published online: 22 SEP 2004
Volume 54, Issue 3, pages 823–835, November 2004
How to Cite
Feng, X., Walthers, D., Oropeza, R. and Kenney, L. J. (2004), The response regulator SsrB activates transcription and binds to a region overlapping OmpR binding sites at Salmonella pathogenicity island 2. Molecular Microbiology, 54: 823–835. doi: 10.1111/j.1365-2958.2004.04317.x
- Issue published online: 22 SEP 2004
- Article first published online: 22 SEP 2004
- Accepted 19 July, 2004.
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 β-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.