Transcriptional regulation and promoter sequence of the spvR gene of virulence plasmid pKDSC50 in Salmonella choleraesuis serovar Choleraesuis.

The transcript of the spvR gene on the virulence plasmid, pKDSC50, of Salmonella choleraesuis serovar Choleraesuis was detected for the first time by Northern blot analysis, and the transcriptional regulation of the spvR gene was investigated. The transcription of the spvR was negatively regulated by spvA and spvB, and enhanced at stationary phase under control of a sigma factor RpoS (sigma 38). The spvR transcript was 2.4 kilonucleotides in Salmonella cells, and deduced to encode SpvR and SpvA, suggesting that SpvA but not SpvB is the functioning repressor in spv operon. The promoter sequence analysis revealed that spvR was transcribed from a single promoter and the 5' end of the transcript was located at 18 bp upstream from the start codon of spvR. Sequential similarity between the promoter of spvR and other sigma 38-controlled genes was not found, but the consensus sequence was found in -10 to -35 region of spvR and spvA, which may correlate to our previous data indicating that both genes were positively regulated by the SpvR protein.