Phosphate starvation regulon of Salmonella typhimurium.

Several phosphate-starvation-inducible (psi) genetic loci in Salmonella typhimurium were identified by fusing the lacZ gene to psi promoters by using the Mu d1 and Mu d1-8 bacteriophages. Although several different starvation conditions were examined, the psi loci responded solely to phosphate deprivation. A regulatory locus, psiR, was identified as controlling the psiC locus. The psiR locus did not affect the expression of the Escherichia coli phoA locus or any of the other psi loci described.     

Regulatory mutants of the deo regulon in Salmonella typhimurium

Summary A method is described for isolating mutants which are constitutive for thymidine phosphorylase. The mutants isolated are also constitutive for all of the enzymes of the deo regulon and are unlinked to the deo genes suggesting that they have a defect in a regulatory gene. We have designated this regulatory gene deo R.     

The control region of the pdu/cob regulon in Salmonella typhimurium.

The pdu operon encodes proteins for the catabolism of 1,2-propanediol; the nearby cob operon encodes enzymes for the biosynthesis of adenosyl-cobalamin (vitamin B12), a cofactor required for the use of propanediol. These operons are transcribed divergently from distinct promoters separated by several kilobases. The regulation of the two operons is tightly integrated in that both require the positive activator protein PocR and both are subject to global control by the Crp and ArcA proteins. We have determined the DNA nucleotide sequences of the promoter-proximal portion of the pdu operon and the region between the pdu and cob operons. Four open reading frames have been identified, pduB, pduA, pduF, and pocR. The pduA and pduB genes are the first two genes of the pdu operon (transcribed clockwise). The pduA gene encodes a hydrophobic protein with 56% amino acid identity to a 10.9-kDa protein which serves as a component of the carboxysomes of several photosynthetic bacteria. The pduF gene encodes a hydrophobic protein with a strong similarity to the GlpF protein of Escherichia coli, which facilitates the diffusion of glycerol. The N-terminal end of the PduF protein includes a motif for a membrane lipoprotein-lipid attachment site as well as a motif characteristic of the MIP (major intrinsic protein) family of transmembrane channel proteins. We presume that the PduF protein facilitates the diffusion of propanediol. The pocR gene encodes the positive regulatory protein of the cob and pdu operons and shares the helix-turn-helix DNA binding motif of the AraC family of regulatory proteins. The mutations cobR4 and cobR58 cause constitutive, pocR-independent expression of the cob operon under both aerobic and anaerobic conditions. Evidence that each mutation is a deletion creating a new promoter near the normal promoter site of the cob operon is presented.     

Cloning and characterization of the L-rhamnose regulon in Salmonella typhimurium LT2.

A Salmonella typhimurium LT2 cosmid library was constructed, and a 46-kb recombinant plasmid was isolated that could complement an Escherichia coli rha mutant. Subsequent subcloning generated a 13.6-kb ClaI restriction fragment that contained a functional regulatory element. By complementation analyses using different subclones, the approximate physical locations of rhaT, rhaC1, rhaC2, rhaB, rhaA, and rhaD were determined. The nucleotide sequence spanning the rhaB and rhaC2 genes was determined.     

Isolation and characterization of the Salmonella typhimurium LT2 xylose regulon

Salmonella DNA was partially digested with EcoRI, and the digest was fractionated to obtain fragments larger than 8 kilobases (kb). These were ligated into EcoRI-cut pBR322, and the mixture was used to transform Salmonella Xyl- cells selecting for ampR xyl+ transformants. A 21- and a 27-kb plasmid were isolated, both of which contained the entire xylose regulon. The xylose regulon was localized to a 6.3-kb segment of a 13.5-kb EcoRI fragment. Subclones were constructed which contained either the genes for D-xylose isomerase and D-xylulokinase or the genes for the D-xylose transport and the D-xylose regulatory factors. The gene order determined by the subcloning experiments is consistent with that determined by genetic mapping. The spots corresponding to D-xylose isomerase and D-xylulokinase subunits were identified in two-dimensional gels of several xylose-induced strains. Each of them had a molecular weight of 45,000 and an isoelectric point of 6.2 +/- 0.1.     

envM genes of Salmonella typhimurium and Escherichia coli.

Conjugation and bacteriophage P1 transduction experiments in Escherichia coli showed that resistance to the antibacterial compound diazaborine is caused by an allelic form of the envM gene. The envM gene from Salmonella typhimurium was cloned and sequenced. It codes for a 27,765-dalton protein. The plasmids carrying this DNA complemented a conditionally lethal envM mutant of E. coli. Recombinant plasmids containing gene envM from a diazaborine-resistant S. typhimurium strain conferred the drug resistance phenotype to susceptible E. coli cells. A guanine-to-adenine exchange in the envM gene changing a Gly codon to a Ser codon was shown to be responsible for the resistance character. Upstream of envM a small gene coding for a 10,445-dalton protein was identified. Incubating a temperature-sensitive E. coli envM mutant at the nonpermissive temperature caused effects on the cells similar to those caused by treatment with diazaborine, i.e., inhibition of fatty acid, phospholipid, and lipopolysaccharide biosynthesis, induction of a 28,000-dalton inner membrane protein, and change in the ratio of the porins OmpC and OmpF.     

Method of isolation of cysteine constitutive mutants of the cysteine regulon in Salmonella typhimurium.

Summary Size and shape of mitochondrial DNA molecules of Schizosaccharomyces pombe were analyzed by electron microscopy. Besides numerous linear molecules, circular molecules ranging from 0.83 m to 12.81 m were found. Depending on the method of preparation, both closed and open circular molecules were found. Most of the circular molecules could be assigned to five major size classes of 0.83±0.05 m, 1.7±0.05 m, 4.74±0.04 m, 5.74±0.04 m, and 8.32±0.07 m. Possible explanations for the different size classes of mitochondrial DNA molecules are discussed.     

Cluster of genes controlling proline degradation in Salmonella typhimurium.

A cluster of genes essential for degradation of proline to glutamate (put) is located between the pyrC and pyrD loci at min 22 of the Salmonella chromosome. A series of 25 deletion mutants of this region have been isolated and used to construct a fine-structure map of the put genes. The map includes mutations affecting the proline degradative activities, proline oxidase and pyrroline-5-carboxylic dehydrogenase. Also included are mutations affecting the major proline permease and a regulatory mutation that affects both enzyme and permease production. The two enzymatic activities appear to be encoded by a single gene (putA). The regulatory mutation maps between the putA gene and the proline permease gene (putP).     

Characterization of the fliL gene in the flagellar regulon of Escherichia coli and Salmonella typhimurium.

filL is a small gene of unknown function that lies within the beginning of a large flagellar operon of Salmonella typhimurium and Escherichia coli. A spontaneous fliL mutant of S. typhimurium, containing a frameshift mutation about 40% from the 3' end of the gene, was moderately motile but swarmed poorly, suggesting that FliL might be a component of the flagellar motor or switch. However, in-frame deletions of the E. coli gene, including an essentially total deletion, had little or no effect on motility or chemotaxis. Thus, FliL does not appear to have a major role in flagellar structure or function and is therefore unlikely to be a component of the motor or switch; the effect on motility caused by truncation of the gene is probably an indirect one.     

Structural genes for flagellar hook-associated proteins in Salmonella typhimurium.

The flaW, flaU, and flaV genes of Salmonella typhimurium LT2 were cloned into pBR322. These genes were mapped on the cloned DNA fragments by restriction endonuclease analysis and construction of the deletion derivatives. Their gene products were identified, by the minicell method, as proteins whose molecular weights were estimated to be 59,000 for the flaW product, 31,000 for the flaU product, and 48,000 for the flaV product. These values are identical to those of three species of hook-associated proteins (HAPs), namely, HAP1, HAP3, and HAP2. Furthermore, antibodies against HAP1, HAP3, and HAP2 specifically reacted with the gene products of flaW, flaU, and flaV, respectively. Therefore, we concluded that they are structural genes for HAPs. The antibodies against HAP1 and HAP3 also specifically reacted with the gene products of flaS and flaT of Escherichia coli, respectively. This indicates that these gene products are HAPs in E. coli. This result is consistent with the demonstration that flaS and flaT of E. coli are functionally homologous with flaW and flaU of S. typhimurium.     

Salmonella SsrB activates a global regulon of horizontally acquired genes

Salmonella enterica is a bacterial pathogen of humans that can proliferate within epithelial cells as well as professional phagocytes of the immune system. This ability requires an S. enterica specific locus termed Salmonella pathogenicity island 2 (SPI-2). SPI-2 encodes a type III secretion system that injects effectors encoded within the island into host cell cytosol to promote virulence. SsrAB is a two-component regulator encoded within SPI-2 that was assumed to activate SPI-2 genes exclusively. Here, it is shown that SsrB in fact activates a global regulon. At least 10 genes outside SPI-2 are SsrB regulated within epithelial and macrophage cells. Nine of these 10 SsrB-regulated genes outside SPI-2 reside within previously undescribed regions of the Salmonella genome. Most share no sequence homology with current database entries. However, one is remarkably homologous to human glucosyl ceramidase, an enzyme involved in the ceramide signalling pathway. The SsrB regulon is modulated by the two-component regulatory systems PhoP/PhoQ and OmpR/EnvZ, and is upregulated in the intracellular microenvironment.