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PubMed1971

Control of expression of the L-arabinose operon in temperature-sensitive mutants of gene araC in Escherichia coli B-r.

Expression of the l-arabinose operon in Escherichia coli B/r is dependent on the temperature of growth of the araC mutants reported in this paper. Analysis of these temperature-sensitive regulatory mutants indicates that both repressor and activator activities are thermolabile. The simplest model to explain the manner in which the operon is controlled is one suggesting that the regulatory gene, araC, codes for a protein which upon synthesis acts as a repressor molecule and prevents operon function. When inducer is added, the repressor undergoes a conformational shift and becomes an activator which switches on enzyme synthesis, provided the repressor concentration is reduced to a sufficiently low level in the cell. These data lend strong support to the model that both activities are the result of the same gene product.

Alleles↗

PubMed1989

(S)-3-hydroxy-3-methylglutaryl coenzyme A reductase, a product of the mva operon of Pseudomonas mevalonii, is regulated at the transcriptional level.

We have cloned and sequenced a 505-base-pair (bp) segment of DNA situated upstream of mvaA, the structural gene for (S)-3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.88) of Pseudomonas mevalonii. The DNA segment that we characterized includes the promoter region for the mva operon. Nuclease S1 mapping and primer extension analysis showed that mvaA is the promoter-proximal gene of the mva operon. Transcription initiates at -56 bp relative to the first A (+1) of the translation start site. Transcription in vivo was induced by mevalonate. Structural features of the mva promoter region include an 80-bp A + T-rich region, and -12, -24 consensus sequences that resemble sequences of sigma 54 promoters in enteric organisms. The relative amplitudes of catalytic activity, enzyme protein, and mvaA mRNA are consistent with a model of regulation of this operon at the transcriptional level.

Base Sequence↗

PubMed1992

Catabolite gene activator protein and integration host factor act in concert to regulate tdc operon expression in Escherichia coli.

Anaerobic expression of the tdcABC operon of Escherichia coli requires cyclic AMP and the catabolite gene activator protein (CAP). Purified CAP binds to a 30-bp sequence in the tdc promoter between positions -55 and -26, and a mutant CAP site with base substitutions at positions -48, -47, and -45 failed to bind CAP and also drastically reduced the beta-galactosidase expression from a tdcB'-'lacZ fusion plasmid. Recently, we showed that efficient expression of the tdc operon also requires a functional integration host factor (IHF) and an IHF-binding site in the tdc promoter between positions -118 and -88. The levels of beta-galactosidase activity from the tdcB'-'lacZ fusion plasmids were also reduced in an IHF-deficient strain with the wild-type or mutant plasmid CAP sequence. In vitro footprinting experiments revealed that CAP and IHF occupy their specific binding sites on tdc DNA when they are present separately or together. These regulatory proteins also induced significant bending of the tdc promoter DNA. Our results suggest that CAP and IHF act in concert as positive transcription factors for tdc operon expression in vivo.

Anaerobiosis↗

PubMed1992

Thermoregulation of the pap operon: evidence for the involvement of RimJ, the N-terminal acetylase of ribosomal protein S5.

Our previous work showed that pap pilin gene transcription is subject to a thermoregulatory control mechanism under which pap pilin is not transcribed at a low temperature (23 degrees C) (L. B. Blyn, B. A. Braaten, C. A. White-Ziegler, D. H. Rolfson, and D. A. Low, EMBO J. 8:613-620, 1989). In order to isolate genes involved in this temperature regulation of gene expression, chromosomal mini-Tn10 (mTn10) mutations that allowed transcription of the pap pilin gene at 23 degrees C were identified, and the locus was designated tcp, for "thermoregulatory control of pap" (C. A. White-Ziegler, L. B. Blyn, B. A. Braaten, and D. A. Low, J. Bacteriol. 172:1775-1782, 1990). In the present study, quantitative analysis showed that the tcp mutations restore pap pilin transcription at 23 degrees C to levels similar to those measured at 37 degrees C. By in vivo recombination, the tcp mutations were mapped to phage E4H10S of the Kohara library of the Escherichia coli chromosome (Y. Kohara, K. Akiyama, and K. Isono, Cell 50:495-508, 1987). The tcp locus was cloned by complementation, in which a 1.3-kb DNA fragment, derived from the Kohara phage, was shown to restore thermoregulation to the mTn10 mutants. DNA sequencing revealed two open reading frames (ORFs) encoding proteins with calculated molecular masses of 22.7 and 20.3 kDa. The sequence of the 22.7-kDa ORF was identical to that of rimJ, the N-terminal acetylase of the ribosomal protein S5. The gene encoding the 20.3-kDa ORF, designated g20.3 here, did not display significant homology to any known DNA or protein sequence. On the basis of Northern (RNA) blot data, rimJ and g20.3 are located within the same operon. Two of the mTn10 transposons in the thermoregulatory mutants were inserted within the coding region of rimJ, indicating that the RimJ protein plays an important role in the temperature regulation of pap pilin gene transcription. However, rimJ itself is not thermoregulated, since rimJ transcripts were detected at both 23 and 37 degrees C. Disruption of the g20.3 gene by insertion and deletion mutagenesis did not affect thermoregulation of the pap operon, suggesting that, although g20.3 lies within the same operon as rimJ, it does not play a role in thermoregulation.

Acetylation↗

PubMed1992

Regulation of the Staphylococcus aureus plasmid pI258 mercury resistance operon.

Experiments involving fusion between the Staphylococcus aureus plasmid pI258-encoded mer operon and the reporter gene beta-lactamase, mutational analysis, and trans-complementation studies have shown that the merR gene of pI258, which shows DNA sequence similarity with known merR genes from other bacteria, regulates the expression of the mer operon in vivo. The merR gene product is a trans-acting protein that activates mer operon transcription in the presence of the inducers Hg2+ and Cd2+. A glutathione-S-transferase-MerR fusion protein specifically bound and protected a 27-nucleotide operator sequence from DNase I digestion. This operator sequence is highly homologous with mer operator sequences of other known systems.

Bacterial Proteins↗

PubMed1992

Autoregulation of the stability operon of IncFII plasmid NR1.

The stb locus of IncFII plasmid NR1, which mediates stable inheritance of the plasmid, is composed of an essential cis-acting DNA site located upstream from two tandem genes that encode essential stability proteins. The two tandem genes, stbA and stbB, are transcribed as an operon from promoter PAB. Using PAB-lacZ gene fusions, it was found that the stb operon is autoregulated. A low-copy-number stb+ plasmid introduced into the same cell with the PAB-lacZ fusion plasmid repressed beta-galactosidase activity about 5-fold, whereas a high-copy-number stb+ plasmid repressed beta-galactosidase about 15-fold. The details of autoregulation were analyzed by varying the concentrations of StbA and StbB to examine their effects on expression from the PAB-lacZ fusion plasmid. StbB protein by itself had autorepressor activity. Although StbA protein by itself had no detectable repressor activity, plasmids that encoded both stbA and stbB repressed more effectively than did those that encoded stbB alone. Plasmids with a mutation in stbA had reduced repressor activity. One mutation in stbB that inactivated the stability function also reduced, but did not eliminate, repressor activity. Repressor activity of the mutant StbB protein was effectively enhanced by stbA. These results indicate that StbB serves two functions, one for stable inheritance and one for autoregulation of the stb operon, both of which may be influenced by StbA protein.

DNA Transposable Elements↗

PubMed2001

The Brucella suis homologue of the Agrobacterium tumefaciens chromosomal virulence operon chvE is essential for sugar utilization but not for survival in macrophages.

Brucella strains possess an operon encoding type IV secretion machinery very similar to that coded by the Agrobacterium tumefaciens virB operon. Here we describe cloning of the Brucella suis homologue of the chvE-gguA-gguB operon of A. tumefaciens and characterize the sugar binding protein ChvE (78% identity), which in A. tumefaciens is involved in virulence gene expression. B. suis chvE is upstream of the putative sugar transporter-encoding genes gguA and gguB, also present in A. tumefaciens, but not adjacent to that of a LysR-type transcription regulator. Although results of Southern hybridization experiments suggested that the gene is present in all Brucella strains, the ChvE protein was detected only in B. suis and Brucella canis with A. tumefaciens ChvE-specific antisera, suggesting that chvE genes are differently expressed in different Brucella species. Analysis of cell growth of B. suis and of its chvE or gguA mutants in different media revealed that ChvE exhibited a sugar specificity similar to that of its A. tumefaciens homologue and that both ChvE and GguA were necessary for utilization of these sugars. Murine or human macrophage infections with B. suis chvE and gguA mutants resulted in multiplication similar to that of the wild-type strain, suggesting that virB expression was unaffected. These data indicate that the ChvE and GguA homologous proteins of B. suis are essential for the utilization of certain sugars but are not necessary for survival and replication inside macrophages.

ATP-Binding Cassette Transporters↗

PubMed1966

Expression of the leucine operon.

Burns, R. O. (Cold Spring Harbor Laboratories of Quantitative Biology, Cold Spring Harbor, N.Y.), J. Calvo, P. Margolin, and H. E. Umbarger. Expression of the leucine operon. J. Bacteriol. 91:1570-1576. 1966.-The four genes which specify the structure of the three enzymes specifically involved in the biosynthesis of leucine in Salmonella typhimurium constitute a single operon. Three types of control mutants have been delineated on the basis of their location on the Salmonella chromosome and the manner in which they coordinately affect the rates of synthesis of the pertinent enzymes. The three types of mutants correspond to operator-negative, operator-constitutive, and regulator-negative. The rate of synthesis of the enzymes can also be altered by varying the amount of leucine made available to the cell. Leucine can be effectively limited by limiting the supply of alpha-ketoisovalerate, but in doing so two of the three enzymes, alpha-isopropylmalate synthetase and isopropylmalate isomerase, are labilized. This observation was correlated with an in vivo diminution of the levels of the substrates of these enzymes and the fact that alpha-ketoisovalerate and alpha-isoporpylmalate protect the respective enzymes against thermal inactivation in vitro. The functional association of the structural genes is also illustrated by the presence of polarity mutations; that is, certain structural gene mutations lower the rates of synthesis of the enzymes specified by genes located distally to the mutated gene and the operator segment of the operon.

Genes↗

PubMed1968

Polar and antipolar mutants in the tryptophan operon of Salmonella typhimurium.

Polar mutations in trpA, the first structural gene of the tryptophan operon of Salmonella typhimurium, have an uncoordinate effect on the expression of the distal genes, with trpB, the second gene, being more drastically affected than the last three. A number of these polar mutant strains grow very poorly on anthranilic acid-supplemented minimal medium. By selecting for more rapid growth in the presence of anthranilic acid, secondary mutant clones showing a correction of the polar effect were isolated. A few of these were analyzed and shown to contain deletions of various segments of the trpA gene. Ten randomly isolated deletion mutants missing various segments of the trp operon were analyzed for possible pleiotropic effects. Five of them showed a pleiotropic effect of some sort and five did not. Of those showing pleiotropic effects, one had lost the promotor-like elements necessary to initiate expression of the operon, three showed possible antipolar effects, and one showed both polar and antipolar effects simultaneously.

Genes↗

PubMed1984

A catabolite-resistance mutation is localized in the rpo operon of Bacillus subtilis.

By transformation analysis, a mutation (crsE1), which makes Bacillus subtilis cells able to sporulate in the presence of relatively high concentrations of glucose and other carbon sources, was mapped in the rpoBC operon. The effect of crsE1 mutation can be suppressed by another mutation in the same operon, rfm11, which confers resistance to rifamycin. Mutants carrying stv or std mutations, which are also located in the rpoBC operon, showed partial resistance to catabolites in sporulation. It appears therefore that a change in the structure or synthesis of RNA polymerase may alter the response of cells to the inhibitory effect of catabolites on sporulation.

Anti-Bacterial Agents↗

PubMed2002

Cloning and characterization of groESL operon in Acetobacter aceti.

The groESL operon of Acetobacter aceti was cloned and sequenced. We observed that GroES and GroEL of A. aceti had high amino acid sequence homologies to GroES and GroEL of Escherichia coli and Bacillus subtilis. The upstream region of the groESL operon contained the heat-shock promoter, which was previously reported in alpha-purple proteobacteria, and the highly conserved inverted repeat sequence. Phylogenetic analysis revealed that the A. aceti GroES and GroEL are very closely related to those of other alpha-purple proteobacteria. Transcription of this operon in A. aceti was induced by heat shock as well as by exposure to ethanol and acetic acid, which are present during fermentation of acetic acid. A. aceti that overexpressed the groESL was more resistant than the control strain to Stressors such as heat, ethanol, or acetic acid, indicating that GroES and GroEL are closely associated with the characteristic nature of Acetobacter and play an important role in acetic acid fermentation.

Journal Article↗

PubMed1997

Cloning and sequencing of the genes for N-acetylglucosamine use that construct divergent operons (nagE-nagAC) from Vibrio cholerae non-O1.

A 7.2-kb genomic DNA fragment containing N-acetylglucosamine-6-phosphate deacetylase gene (nagA) was cloned from the chitinase-producing bacterium Vibrio cholerae non-O1 strain 1148A (IFO 15429). Sequence analysis of the DNA fragment found three other complete open reading frames (ORFs) and the 5' end of an ORF. Amino acid sequences of two ORFs, ORF2 and ORF4, showed similarity with that of NagC, the repressor of nag operons and that of NagE, N-acetylglucosamine-specific transporter II(Nag) of phosphoenolpyruvate transport system of Escherichia coli, respectively. In the presence of N-acetylglucosamine, nagA and ORF2 (nagC) were co-transcribed. ORF4 (nagE), which is upstream from nagAC but is expressed in the opposite direction was also transcriptionally induced in the presence of N-acetylglucosamine. These results indicated that nagE-nagAC existed as divergent operons in V. cholerae non-O1. Unlike E. coli, nagB and nagD were not in the operons.

Acetylglucosamine↗

PubMed2002

Molecular characterization and regulatory analysis of dnaK operon of halophilic lactic acid bacterium Tetragenococcus halophila.

We have cloned and characterized the dnaK operon of Tetragenococcus halophila JCM5888. Nucleotide sequence analysis of cloned fragments showed that the dnaK operon consists of four open reading frames with the organization hrcA-grpE-dnaK-dnaJ. Two regulatory CIRCE (Controlling Inverted Repeat of Chaperone Expression) elements were identified in the region up-stream of hrcA. The T. halophila dnaK encoded a protein of 618 amino acids with a calculated molecular mass of 67 kDa. The deduced amino acid sequence of T. halophila DnaK showed high similarities with those of the corresponding DnaK homologues of Lactococcus lactis, Lactobacillus sakei and Bacillus subtilis. Using a pET expression system, the T. halophila DnaK was overexpressed in Escherichia coli and the purified DnaK was found to exhibit ATPase and refolding activities. Northern hybridization analysis revealed that the transcription of the dnaK gene was induced by heat shock, and several transcripts were detected including a tetra-cistronic mRNA with a maximum size of 4.9-kb which corresponds to the transcript of the complete dnaK operon. The amount of dnaK transcripts increased about 3.5-fold at high NaCl concentration of 3-4 M, but not at the same KCl concentrations. These results suggest that the cloned DnaK acts as a functional molecular chaperone and plays an important role in salinity adaptation.

Journal Article↗

PubMed1988

ack::Mu d1-8 (Apr lac) operon fusions of Salmonella typhimurium LT2.

Several ack::Mu d1-8 insertions were isolated from Salmonella typhimurium on MacConkey-glucose-trimethylamine oxide medium. They could not produce gas from glucose in the absence of exogenous formate. Two of the mutants expressed beta-galactosidase activity and were shown to be ack::Mu d1-8 fusions by genetic analysis. These insertions were characterized and located on the genetic map at the ack locus by co-transduction with zei::Tn10. The gene order zei::Tn10-ack-pta was established. The direction of transcription of ack was clockwise on the genetic map. Expression of the lac operon in ack::Mu d1-8 was increased twofold by anaerobiosis. Addition of formate, pyruvate, and acetate did not affect the anaerobic expression of the lac operon in ack::Mu d1-8.

Acetate Kinase↗

PubMed1990

Two different mechanisms for urea action at the LAC and TNA operons in Escherichia coli.

Urea, at concentrations which do not interfere with bacterial growth, specifically inhibits the expression of catabolite sensitive operons. To search for the target and the mechanism of urea action we measured lactose (lac) and tryptophanase (tna) specific mRNA synthesis in vivo and in vitro. We show that urea acts by two different mechanisms at these two catabolite sensitive operons, resembling the manner in which catabolite repression regulates lac and tna. At the lac promoter, urea abolishes transcription initiation or blocks an early step in mRNA elongation without interfering with the binding of RNA polymerase and catabolite gene activator protein (CAP). At the tna promoter, urea does not abolish transcription initiation but could interfere with tnaC translation.

Cyclic AMP Receptor Protein↗

PubMed2005

Structural organization of the transfer RNA operon I of Vibrio cholerae: differences between classical and El Tor strains.

Nine major transfer RNA (tRNA) gene clusters were analysed in various Vibrio cholerae strains. Of these, only the tRNA operon I was found to differ significantly in V. cholerae classical (sixth pandemic) and El Tor (seventh pandemic) strains. Amongst the sixteen tRNA genes contained in this operon, genes for tRNA Gln3 (CAA) and tRNA Leu6 (CUA) were absent in classical strains as compared to El Tor strains. The observation strongly supported the view that the above two pandemic strains constitute two different clones.

Operon↗

PubMed1984

Nucleotide sequence of the promoter region of the melibiose operon of Escherichia coli.

The nucleotide sequence of the promoter region of the melibiose operon of E. coli was determined. Consensus sequences for the -35 region, the Pribnow box and the binding site for cyclic AMP receptor protein were found in this region. The possible secondary structure of this DNA region was very similar to that of the promoter region of the lactose operon. A possible initiation ATG preceded by a Shine-Dalgarno sequence with proper spacing was present just downstream of the promoter region. The possible sequence of 52 amino acid residues in the NH2 terminus of the alpha-galactosidase were determined.

Amino Acid Sequence↗

PubMed1992

Broad host range plasmids carrying the Escherichia coli lactose and galactose operons.

We have developed a number of broad-host-range plasmids that allow the expression of the Escherichia coli lac operon from any cloned promoter, and the creation of 'in phase' fusions between lacZ and other cloned genes. In a second series of constructions, the E. coli gal operon has been cloned into the broad-host-range vector and a plasmid carrying both the E. coli gal and lac genes is described. These plasmids have been transferred into Pseudomonas aeruginosa and Zymomonas mobilis and their effects on the utilisation of lactose and galactose have been investigated.

Escherichia coli↗