We establish that the PmrA protein represses transcription of ssrB .
the ssrB promoter abolished repression by the PmrA protein
We establish that the PmrA protein down-regulates expression of spi/ssa genes by repressing transcription from the ssrB promoter .
The hypervirulence of the pmrA null mutant can be recapitulated by rendering the ssrB promoter resistant to repression by PmrA .
The PmrA protein appears to repress ssrB directly because : First , the purified PmrA protein protected the − 45 to − 16 region from ATG of of the ssrB gene in-vitro -LRB- Fig .
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Taken together , the results indicate that PmrA 
To examine the physiological consequences of PmrA repression of ssrB transcription , we examined the kinetics of SPI-2 -- promoted macro-phage death .
The results presented above suggested that the hypervirulence phenotype of the pmrA null mutant might be due to PmrA repression of ssrB transcription .
the ssrB promoter mutant is refractory to repression by the PmrA protein
The antivirulence function of PmrA can be ascribed to its role as transcriptional repressor of the regulatory gene ssrB .
These results suggest that PmrA repression of ssrB might enable Salmonella to favor dissemination to neighboring cells .
These results suggest that PmrA repression of ssrB might enable Salmonella to control bacterial proliferation within a cell .
Moreover , it suggests that one of the roles of PhoP in promoting ssrB transcription might be to overcome PmrA-dependent repression of ssrB .
Interestingly , the PmrA protein repressed SPI-2 expression in a manner similar to the Fur regulator ; PmrA was shown to repress ssrB transcription .