ROLE OF RPOS IN THE REGULATION OF SALMONELLA PLASMID VIRULENCE (SPV) GENES

Salmonella plasmid virulence (spv) genes are organized into two transc riptional units: one formed by the spvR gene and the other by the spvA , spvB, spvC and spvD genes. Transcription of both units is activated by SpvR, a regulatory protein of the LysR family. The effect of RpoS, a stationary phase-associated sigma factor, on the expression of spu g enes was studied using lacZ transcriptional fusions to spvR and spvA i n wild-type and rpoS Escherichia coli backgrounds. Mutant and wild-typ e SpvR proteins were expressed in trans from a multicopy plasmid. The results show that the combined action of rpoS and spvR is necessary fo r transcription of spvA and that this combination also enhances transc ription of spvR. Interestingly, spvR can also be transcribed in an alt ernative manner, i.e. in the absence of rpoS or spvR or both. The poss ible role for SpvR as a repressor of its own transcription is discusse d.