THE SALMONELLA-TYPHIMURIUM KATF (RPOS) GENE - CLONING, NUCLEOTIDE-SEQUENCE, AND REGULATION OF SPVR AND SPVABCD VIRULENCE PLASMID GENES

The spv region of Salmonella virulence plasmids is essential for the d evelopment of a systemic infection in mice, Transcriptional activation of the spvABCD operon occurs during stationary growth phase and is me diated by the regulatory gene product SpvR. We have previously shown t hat expression of a spvRAB'-cat fusion in Escherichia coli was depende nt on the katF (rpoS) locus which encodes an alternative sigma factor (sigma(S)). The katF gene from Salmonella typhimurium has been cloned, sequenced, and used to construct Salmonella katF mutants by allelic r eplacement. Using these mutants, we demonstrated by mRNA and gene fusi on analyses that sigma(S), in conjunction with SpvR, controls the tran scription of the regulatory gene spvR. In a second series of experimen ts, we sought to clarify the relationship between sigma(S) and SpvR in the control of spvABCD transcription. It was shown that expression of a transcriptional spvAB'-lacZ fusion could be restored in E. coli and Salmonella katF mutants when spvR was expressed in trans from an exog enous promoter. Moreover, identical spvA mRNA startpoints were detecte d in katF(+) and katF strains. These results indicate that the reducti on of spvABCD transcription in katF mutants is mainly due to decreased expression of spvR. Finally, mouse inoculation studies with S. typhim urium katF mutants of both wild-type and virulence plasmid-cured strai ns suggest that katF contributes to Salmonella virulence via the regul ation of chromosomal genes in addition to that of spv genes.