The mkaC virulence gene of the Salmonella serovar Typhimurium 96 kb plasmid encodes a transcriptional activator

Abstract

The intracellular growth and virulence of Salmonella serovar Typhimurium for mice is dependent on a plasmid-borne gene cluster termed mka. We studied the regulatory interactions of the genes mkaA, mkaB, mkaC and mkaD using lacZ gene fusions. Complementation experiments with cloned DNA fragments encoding each of the four MKa proteins indicated that mkaC enhances the expression of beta-galactosidase from the mkaA-, mkaB- and mkaC-lacZ gene fusions in trans. An mkaD-lacZ fusion or mkaA-lacZ fusion that did not contain DNA proximal to mkaB was not inducible with MkaC, indicating that at least mkaB and mkaA are induced together as an operon. MkaC is thus the first virulence protein whose function has been resolved.

Analysis of a Rhizobium leguminosarum gene encoding a protein homologous to glutathione S-transferases

“…As shown in Table 2, in the wildtype background, expression of gstA-ZacZ was at a low level whereas that of gstR-lacZ was relatively high. This is consistent with most other examples of the LysR family, in which the regulatory gene is expressed constitutively but the regulated genes are only transcribed at high levels when bacteria are exposed to an appropriate inducer (Schell, 1993 In most examples of the LysR family, the regulatory gene represses its own transcription independently of the presence of an inducer molecule (see Schell, 1993), although there are exceptions to this (Smit et al, 1992;Taira et al, 1991). Activation of transcription of any ' target' genes normally requires an inducer; it remains to be seen if gstR does in fact regulate g s t A but that this only occurs in the presence of some as yet unidentified inducer molecule.…”

Regulation of plasmid virulence gene expression in Salmonella dublin involves an unusual operon structure

“…These observations appear to contradict the report of Williamson et al, which suggested that spvA regulates the expression of spvR (45). Taira et al have found that spvA and spvB are expressed as a unit; however, conclusive evidence demonstrating the presence of an spv operon is still lacking (37,40). The head-to-tail orientation of the spvA, spvB, spvC, and spvD genes suggests a polycistronic transcription of the region, although the intergenic sequences of 180 to 280 nucleotides between the genes are unusually long for a classical bacterial operon (21,30).…”

“…Amino acid homology and recent published data suggested that spvR encodes a protein with a transcriptional activator function (4,8,25,40). To establish spvR-dependent regulation of spvA, spvB, spvC, and spvD, we analyzed their transcription with and without the presence of SpvR by comparing pSDL2 and pSD15-2.…”

The Salmonella typhimurium katF (rpoS) gene: cloning, nucleotide sequence, and regulation of spvR and spvABCD virulence plasmid genes

“…In contrast with this result, an spvR'-lacZ fusion (pSTF12) expressed a very low level of ,3-galactosidase activity in katF and katF strains (Table 3). Since it was previously shown that the spvR gene was subjected to positive autoregulation (11,41), we hypothesized that the SpvR protein was required for the katF-dependent expression of the spvR'-lacZ fusion. Two findings corroborated this hypothesis.…”