The cya gene region of Erwinia chrysanthemi B374: organisation and gene products

Use of RP4::Mini-Mu for Gene Transfer

Gene cloning is an invaluable technique in genetic analysis and exploitation of genetic properties of a broad range of bacteria. Numerous in vitro molecular cloning protocols have been devised but the efficiency of these techniques relies on the frequency with which the recombinant DNA can be introduced in the recipient strain. Here, we describe an in vivo gene transfer and cloning technique based on transposable bacteriophage Mu property to rearrange its host genome. This technique uses the broad host range plasmid RP4 carrying a transposable mini-MuA⁺ derivative and was successfully used as well in enteric as in environmental nonenteric bacteria.

Chemical activation of adenylyl cyclase Rv1625c inhibits growth of Mycobacterium tuberculosis on cholesterol and modulates intramacrophage signaling

Mycobacterium tuberculosis (Mtb) uses a complex 3', 5'-cyclic AMP (cAMP) signaling network to sense and respond to changing environments encountered during infection, so perturbation of cAMP signaling might be leveraged to disrupt Mtb pathogenesis. However, understanding of cAMP signaling pathways is hindered by the presence of at least 15 distinct adenylyl cyclases (ACs). Recently, the small molecule V-58 was shown to inhibit Mtb replication within macrophages and stimulate cAMP production in Mtb. Here we determined that V-58 rapidly and directly activates Mtb AC Rv1625c to produce high levels of cAMP regardless of the bacterial environment or growth medium. Metabolic inhibition by V-58 was carbon source dependent in Mtb and did not occur in Mycobacterium smegmatis, suggesting that V-58-mediated growth inhibition is due to interference with specific Mtb metabolic pathways rather than a generalized cAMP toxicity. Chemical stimulation of cAMP production by Mtb within macrophages also caused down regulation of TNF-α production by the macrophages, indicating a complex role for cAMP in Mtb pathogenesis. Together these studies describe a novel approach for targeted stimulation of cAMP production in Mtb, and provide new insights into the myriad roles of cAMP signaling in Mtb, particularly during Mtb's interactions with macrophages.

Control of catalysis in globin coupled adenylate cyclase by a globin-B domain

The globin coupled heme containing adenylate cyclase from Leishmania major (HemAC-Lm) has two globin domains (globin-A and globin-B). Globin-B domain (210-360 amino acids) may guide the interaction between globin-A and adenylate cyclase domains for the regulation of catalysis. We investigated the role of globin-B domain in HemAC-Lm by constructing a series of mutants namely Δ209 (209 amino acids deleted), Δ360 (360 amino acids deleted), H161A, H311A and H311A-Δ209. Spectroscopic data suggest that the Δ209 and H311A-Δ209 proteins to be Fe(2+)-O2 form and apo form, respectively, indicating that His311 residue in the globin-B domain is crucial for heme binding in Δ209 protein. However, the H311A mutant is still of the Fe(2+)-O2 form whereas H161A mutant shows the apo form, indicating that only His161 residue in the globin-A domain is responsible for heme binding in full length enzyme. cAMP measurements suggest that the activities of Δ360 and Δ209 proteins were ∼10 and ∼1000 times lesser than full length enzyme, respectively, leading to the fact that globin-B domain inhibited catalysis rather than activation in absence of globin-A domain. These data suggest that the O2 bound globin-A domain in HemAC-Lm allows the best cooperation of the catalytic domain interactions to generate optimum cAMP.

SrfJ, a Salmonella type III secretion system effector regulated by PhoP, RcsB, and IolR

Virulence-related type III secretion systems are present in many Gram-negative bacterial pathogens. These complex devices translocate proteins, called effectors, from the bacterium into the eukaryotic host cell. Here, we identify the product of srfJ, a Salmonella enterica serovar Typhimurium gene regulated by SsrB, as a new substrate of the type III secretion system encoded by Salmonella pathogenicity island 2. The N-terminal 20-amino-acid segment of SrfJ was recognized as a functional secretion and translocation signal specific for this system. Transcription of srfJ was positively regulated by the PhoP/PhoQ system in an SsrB-dependent manner and was negatively regulated by the Rcs system in an SsrB-independent manner. A screen for regulators of an srfJ-lacZ transcriptional fusion using the T-POP transposon identified IolR, the regulator of genes involved in myo-inositol utilization, as an srfJ repressor. Our results suggest that SrfJ is synthesized both inside the host, in response to intracellular conditions, and outside the host, in myo-inositol-rich environments.

Analysis of the expression, secretion and translocation of the Salmonella enterica type III secretion system effector SteA

Many Gram-negative pathogens possess virulence-related type III secretion systems. Salmonella enterica uses two of these systems, encoded on the pathogenicity islands SPI-1 and SPI-2, respectively, to translocate more than 30 effector proteins into eukaryotic host cells. SteA is one of the few effectors that can be translocated by both systems. We investigated the conditions affecting the synthesis of this effector, its secretion to culture media and its translocation into host cells. Whereas steA was expressed under a wide range of conditions, some factors, including low and high osmolarity, and presence of butyrate, decreased expression. SteA was efficiently secreted to the culture media under both SPI-1 and SPI-2 inducing conditions. The kinetics of translocation into murine macrophages and human epithelial cells was studied using fusions with the 3xFLAG tag, and fusions with CyaA from Bordetella pertussis. Translocation into macrophages under non-invasive conditions was mainly dependent on the SPI-2-encoded type III secretion system but some participation of the SPI-1 system was also detected 6 hours post-infection. Interestingly, both type III secretion systems had a relevant role in the translocation of SteA into epithelial cells. Finally, a deletion approach allowed the identification of the N-terminal signal necessary for translocation of this effector. The amino acid residues 1–10 were sufficient to direct translocation into host cells through both type III secretion systems. Our results provide new examples of functional overlapping between the two type III secretion systems of Salmonella.

Regulatory exaptation of the catabolite repression protein (Crp)-cAMP system in Pseudomonas putida

The genome of the soil bacterium Pseudomonas putida KT2440 encodes singular orthologues of genes crp (encoding the catabolite repression protein, Crp) and cyaA (adenylate cyclase) of Escherichia coli. The levels of cAMP formed by P. putida cells were below detection with a Dictyostelium biosensor in vivo. The cyaA(P. putida) gene was transcribed in vivo but failed to complement the lack of maltose consumption of a cyaA mutant of E. coli, thereby indicating that cyaA(P. putida) was poorly translated or rendered non-functional in the heterologous host. Yet, generation of cAMP by CyaA(P. putida) could be verified by expressing the cyaA(P. putida) gene in a hypersensitive E. coli strain. On the other hand, the crp(P. putida) gene restored the metabolic capacities of an equivalent crp mutant of E. coli, but not in a double crp/cyaA strain, suggesting that the ability to regulate such functions required cAMP. In order to clarify the breadth of the Crp/cAMP system in P. putida, crp and cyaA mutants were generated and passed through a battery of phenotypic tests for recognition of gross metabolic properties and stress-endurance abilities. These assays revealed that the loss of each gene led in most (but not all) cases to the same phenotypic behaviour, indicating a concerted functionality. Unexpectedly, none of the mutations affected the panel of carbon compounds that can be used by P. putida as growth substrates, the mutants being impaired only in the use of various dipeptides as N sources. Furthermore, the lack of crp or cyaA had little influence on the gross growth fingerprinting of the cells. The poor physiological profile of the Crp-cAMP system of P. putida when compared with E. coli exposes a case of regulatory exaptation, i.e. the process through which a property evolved for a particular function is co-opted for a new use.

Bacillus subtilis genome project: cloning and sequencing of the 97 kb region from 325° to 333deg

In the framework of the European project aimed at the sequencing of the Bacillus subtilis genome the DNA region located between gerB (314°) and sacXV (333°) was assigned to the Institut Pasteur. In this paper we describe the cloning and sequencing of a segment of 97 kb of contiguous DNA. Ninety-two open reading frames were predicted to encode putative proteins among which only forty-two were found to display significant similarities to known proteins present in databanks, e.g. amino acid permeases, proteins involved in cell wall or antibiotic biosynthesis, various regulatory proteins, proteins of several dehydrogenase families and enzymes II of the phosphotransferase system involved in sugar transport. Additional experiments led to the identification of the products of new B. subtilis genes, e.g. galactokinase and an operon involved in thiamine biosynthesis.

Analysis of teichoic acid biosynthesis regulation reveals that the extracytoplasmic function sigma factor σ M is induced by phosphate depletion in Bacillus subtilis W23

The expression of the Bacillus subtilis W23 tar genes specifying the biosynthesis of the major wall teichoic acid, the poly(ribitol phosphate), was studied under phosphate limitation using lacZ reporter fusions. Three different regulation patterns can be deduced from these β-galactosidase activity data: (i) tarD and tarL gene expression is downregulated under phosphate starvation; (ii) tarA and, to a minor extent, tarB expression after an initial decrease unexpectedly increases; and (iii) tarO is not influenced by phosphate concentration. To dissect the tarA regulatory pattern, its two promoters were analysed under phosphate limitation: The P tarA -ext promoter is repressed under phosphate starvation by the PhoPR two-component system, whereas, under the same conditions, the P tarA -int promoter is upregulated by the action of an extracytoplasmic function (ECF) σ factor, σ M. In contrast to strain 168, σ M is activated in strain W23 in phosphate-depleted conditions, a phenomenon indirectly dependent on PhoPR, the two-component regulatory system responsible for the adaptation to phosphate starvation. These results provide further evidence for the role of σ M in cell-wall stress response, and suggest that impairment of cell-wall structure is the signal activating this ECF σ factor.

Effects of global regulatory proteins and environmental conditions on fimbrial gene expression of F165(1) and F165(2) produced by Escherichia coli causing septicaemia in pigs

Escherichia coli O115:F165 strains are associated with septicaemia in young pigs and possess at least two types of fimbriae. F165(1) fimbriae belong to the P fimbrial family and F165(2) fimbriae belong to the S fimbrial family. Regulatory regions of foo (F165(1)) and fot (F165(2)) fimbrial gene clusters from wild-type strain 4787 were sequenced and characterised. Expression of F165(1) and F165(2) fimbrial genes was analysed by using lacZ and/or luxAB as reporter genes under the control of the native fimbrial promoters. Differential expression of fimbrial genes was observed. Global regulatory mechanisms such as catabolite repression, leucine-responsive regulatory protein (Lrp), methylation and DNA supercoiling were demonstrated to influence foo and fot expression. foo and fot expression was optimal at 37 degrees C and under aerobic conditions. Expression of foo was higher on minimal medium, whereas fot expression was higher on complex Luria-Bertani medium. This could reflect an in vivo differential expression.

In vivo induction of CTL responses by recombinant adenylate cyclase of Bordetella pertussis carrying multiple copies of a viral CD8(+) T-cell epitope

Bordetella pertussis adenylate cyclase toxin (ACT) is one of the few known protein toxins penetrating directly into the cytosol of target cells across their cytoplasmic membrane without the need for endocytosis. This capacity of ACT was recently exploited for in vivo delivery of single viral CD8(+) T-epitopes into MHC class I-presenting cells and induction of protective antiviral cytotoxic T-cell (CTL) responses. Here, we have explored the potential of the cell-invasive adenylate cyclase domain of the toxin to deliver larger antigens by evaluating the epitope-specific CTL responses induced by constructs bearing one to four copies of the CD8(+) T-epitope from the nucleoprotein of the lymphocytic choriomeningitis virus. The increase in the number of copies of the epitope was accompanied by a moderate decrease of the specific cell invasiveness of the ACT protein and did not lead to further enhancement of the level of induced epitope-specific CTL cells in mice, as compared to ACT with a single copy of the epitope. These results demonstrate the capacity of ACT to deliver larger heterologous antigens comprising several epitopes for antigenic presentation in vivo.

The Staphylococcus aureus alternative sigma factor sigmaB controls the environmental stress response but not starvation survival or pathogenicity in a mouse abscess model

The role of sigmaB, an alternative sigma factor of Staphylococcus aureus, has been characterized in response to environmental stress, starvation-survival and recovery, and pathogenicity. sigmaB was mainly expressed during the stationary phase of growth and was repressed by 1 M sodium chloride. A sigB insertionally inactivated mutant was created. In stress resistance studies, sigmaB was shown to be involved in recovery from heat shock at 54 degreesC and in acid and hydrogen peroxide resistance but not in resistance to ethanol or osmotic shock. Interestingly, S. aureus acquired increased acid resistance when preincubated at a sublethal pH 4 prior to exposure to a lethal pH 2. This acid-adaptive response resulting in tolerance was mediated via sigB. However, sigmaB was not vital for the starvation-survival or recovery mechanisms. sigmaB does not have a major role in the expression of the global regulator of virulence determinant biosynthesis, staphylococcal accessory regulator (sarA), the production of a number of representative virulence factors, and pathogenicity in a mouse subcutaneous abscess model. However, SarA upregulates sigB expression in a growth-phase-dependent manner. Thus, sigmaB expression is linked to the processes controlling virulence determinant production. The role of sigmaB as a major regulator of the stress response, but not of starvation-survival, is discussed.

A 35.7 kb DNA fragment from the Bacillus subtilis chromosome containing a putative 12.3 kb operon involved in hexuronate catabolism and a perfectly symmetrical hypothetical catabolite-responsive element

The Bacillus subtilis strain 168 chromosomal region extending from 109 degrees to 112 degrees has been sequenced. Among the 35 ORFs identified, cotT and rapA were the only genes that had been previously mapped and sequenced. Out of ten ORFs belonging to a single putative transcription unit, seven are probably involved in hexuronate catabolism. Their sequences are homologous to Escherichia coli genes exuT, uidB, uxaA, uxaB, uxaC, uxuA and uxuB, which are all required for the uptake of free D-glucuronate, D-galacturonate and beta-glucuronide, and their transformation into glyceraldehyde 3-phosphate and pyruvate via 2-keto-3-deoxygluconate. The remaining three ORFs encode two dehydrogenases and a transcriptional regulator. The operon is preceded by a putative catabolite-responsive element (CRE), located between a hypothetical promoter and the RBS of the first gene. This element, the longest and the only so far described that is fully symmetrical, consists of a 26 bp palindrome matching the theoretical B. subtilis CRE sequence. The remaining predicted amino acid sequences that share homologies with other proteins comprise: a cytochrome P-450, a glycosyltransferase, an ATP-binding cassette transporter, a protein similar to the formate dehydrogenase alpha-subunit (FdhA), protein similar to NADH dehydrogenases, and three homologues of polypeptides that have undefined functions.

Expression of a pepT homologue from Bacillus subtilis

We isolated pepT from Bacillus subtilis, a gene with homology to various tripeptidases from different bacterial sources. pepT is preceded by genes encoding a two component regulatory system. Its expression is activated during stationary phase. In minimal medium this activation is boosted in the presence of phosphate. The response regulator is preceded by putative promoter consensus sequences recognized by the stationary phase specific sigma factors sigma H, sigma F, and sigma G. This is in accordance with the initiation of expression at the beginning of stationary phase. Inactivation of pepT causes no obvious phenotype.

Sequencing and functional analysis of the genome of Bacillus subtilis strain 168

The international programme to sequence the 4.2 Mb genome of Bacillus subtilis, a model Gram-positive bacterium, is a joint project involving European, Japanese and US research groups. To date ca. 3.0 Mb of the genome has been sequenced, with the remaining 1.2 Mb expected to be completed in 1997. The amenability of B.subtilis to genetic manipulation, combined with the availability of extensive expertise on its biochemistry and physiology, makes this bacterium a valuable organism in which to investigate the properties of genes for which functions cannot be readily ascribed by standard methods.

Comparative analysis of the cya locus in enterobacteria and related gram-negative facultative anaerobes

Comparison of the cya loci (cya codes for adenylyl cyclase (AC)) from a variety of phylogenetically divergent facultative anaerobic Gram-negative bacteria reveals conserved sequence features. The entire locus structure in enterobacteria is preserved, including two major promoters (a conserved cya strong promoter, P2, and a divergent promoter for a heme biosynthetic operon, hemCD) present in the upstream region of the cya gene. The region between hemC and cya is much longer in Proteus mirabilis than in other enterobacteria, and lacks the P1 upstream cya promoter. In Aeromonas hydrophila the cya promoter (the strong P2 promoter in E coli) is preserved, including a putative GATC methylation site situated immediately downstream from the -10 box. Each cya frame analyzed uses TTG as the translation start codon and is preceded by an unusual ribosome binding site. This suggests that a lower translation efficiency of the cya transcript could be the result of some selection pressure. This has been substantiated by in vitro mutagenesis and by selection of up mutations which all map at the cya ribosome binding site. In enterobacteria the cyaY frame is the only conserved reading frame downstream of cya, with the orientation opposite to that of cya. This organization is not preserved in Aeromonas. Experiments involving fusions with the lacZ gene demonstrated that cyaY is expressed. Finally, comparison of the different polypeptide sequences of ACs permits discussion of important features of the catalytic and regulatory centers of the protein.

Functional analysis of subunits III and IV of Bacillus subtilis aa3-600 quinol oxidase by in vitro mutagenesis and gene replacement

Using the high efficiency of homologous gene recombination in Bacillus subtilis, a strategy for mutational analysis of the proton pumping aa3-600 quinol oxidase of this organism has been developed. The qox operon with the qoxA, qoxB, qoxC and qoxD genes, coding for the four subunits of this oxidase, was deleted and then replaced with mutated copies in which qoxC (subunit III) or qoxD (subunit IV) genes were deleted. The complete deletion of the qox operon caused disappearance of heme aa3-600 and a slight depression of the overall respiratory activity, compensated by alternative oxidase with no proton pumping activity. Deletion of qoxC probably resulted in a defective assembly of the aa3-600 quinol oxidase. The strain with deletion of qoxD gene expressed normal content of heme aa3-600 but exhibited a reduced respiratory activity and a significantly depressed proton pumping activity. These results show that subunit IV is critical for the activity of the proton pumping aa3-600 quinol oxidase.

Cloning of the second adenylate cyclase gene (cya2) from Rhizobium meliloti F34: sequence similarity to eukaryotic cyclases

A second adenylate cyclase (cya2) gene was isolated from a Rhizobium meliloti F34 gene bank. Complemented E. coli delta cya mutants were capable of utilizing a number of, but not all, carbon sources known to be regulated by cAMP. DNA hybridization studies showed cya2 to be unique to R. meliloti strains. The cya2 nucleotide sequence was determined and found to encode a protein of 363 amino acids. Residues were identified within the C-terminal domain which are conserved in both eukaryotic adenylate and guanylate cyclases, including a putative ATP binding site. Similar residues were also found in the prokaryotic R. meliloti Cya1 protein. A R. meliloti cya1/cya2 double mutant was constructed and characterized; however, cAMP production was still observed in this strain indicating the presence of a third cya gene.

The adenylate cyclase catalytic domain of Streptomyces coelicolor is carboxy-terminal

A DNA fragment of Streptomyces coelicolor encoding the carboxy-terminal catalytic domain of adenylate cyclase was cloned, sequenced and expressed in an Escherichia coli cya-defective strain where it produced nanomole levels of cAMP. The amino acid sequence of the enzyme displays similarities with the Brevibacterium liquefaciens pyruvate regulated adenylate cyclase.

Structural and functional relationships between Pasteurella multocida and enterobacterial adenylate cyclases

The Pasteurella multocida adenylate cyclase gene has been cloned and expressed in Escherichia coli. The primary structure of the protein (838 amino acids) deduced from the corresponding nucleotide sequence was compared with that of E. coli. The two enzymes have similar molecular sizes and, based on sequence conservation at the protein level, are likely to be organized in two functional domains: the amino-terminal catalytic domain and the carboxy-terminal regulatory domain. It was shown that P. multocida adenylate cyclase synthesizes increased levels of cyclic AMP in E. coli strains deficient in the catabolite gene activator protein compared with wild-type strains. This increase does not occur in strains deficient in both the catabolite gene activator protein and enzyme III-glucose, indicating that a protein similar to E. coli enzyme III-glucose is involved in the regulation of P. multocida adenylate cyclase. It also indicates that the underlying process leading to enterobacterial adenylate cyclase activation has been conserved through evolution.

A pyruvate-stimulated adenylate cyclase has a sequence related to the fes/fps oncogenes and to eukaryotic cyclases

The pyruvate-stimulated adenylate cyclase from Brevibacterium liquefaciens produces up to 450 microM cyclic AMP in the culture medium when the bacterium is grown on glucose and alanine. In this paper we report the cloning, expression and sequencing of the gene for this enzyme. Residues were identified, within the C-terminal domain, which are conserved in adenylate and guanylate cyclase sequences from eukaryotes and in the adenylate cyclase of the prokaryote Rhizobium meliloti. We have also identified a sequence of 30 residues near the N-terminus of the protein which is homologous to part of the regulatory domain of the cellular homologues of the oncogenes fes and fps; this sequence is also present in the avian Fujinami sarcoma virus fps gene.

A Xanthomonas campestris pv. campestris protein similar to catabolite activation factor is involved in regulation of phytopathogenicity

A DNA fragment from Xanthomonas campestris pv. campestris that partially restored the carbohydrate fermentation pattern of a cya crp Escherichia coli strain was cloned and expressed in E. coli. The nucleotide sequence of this fragment revealed the presence of a 700-base-pair open reading frame that coded for a protein highly similar to the catabolite activation factor (CAP) of E. coli (accordingly named CLP for CAP-like protein). An X. campestris pv. campestris clp mutant was constructed by reverse genetics. This strain was not affected in the utilization of various carbon sources but had strongly reduced pathogenicity. Production of xanthan gum, pigment, and extracellular enzymes was either increased or decreased, suggesting that CLP plays a role in the regulation of phytopathogenicity.

Rhizobium meliloti adenylate cyclase is related to eucaryotic adenylate and guanylate cyclases

A gene from Rhizobium meliloti coding for an adenylate cyclase was sequenced, and the deduced protein sequence was compared with those of other known adenylate cyclases. No similarity could be detected with the procaryotic counterparts. However, striking similarity was found with the catalytic region of Saccharomyces cerevisiae adenylate cyclase, the cytoplasmic domains of bovine adenylate cyclase, and two mammalian guanylate cyclases. The gene was fused to the enteric beta-galactosidase, and the chimeric protein was purified by affinity chromatography. This fusion protein was found to direct the synthesis of cyclic AMP in vitro. This activity was strongly inhibited by the presence of GTP, but no cyclic GMP synthesis could be detected in conditions permitting cyclic AMP synthesis.

Cloning and expression of mouse-brain calmodulin as an activator of Bordetella pertussis adenylate cyclase in Escherichia coli

Cloning of higher eukaryotic genes has seldom been performed by complementation of a defective prokaryotic function. This is especially true in the case of functions that are normally absent from the prokaryotic host. We demonstrate here that it is possible to identify by complementation the cDNA from mouse brain, which encodes calmodulin (CaM) synthesis, in spite of the fact that the recipient strain, Escherichia coli, does not normally harbour a CaM function. A three-component cloning procedure in which a gene product requiring CaM for activity, adenylate cyclase from the pathogen Bordetella pertussis, was used to screen a cDNA library for cAMP synthesis in E. coli. The nucleotide sequence of the corresponding cDNA is also reported.

Structural homology between virulence-associated bacterial adenylate cyclases

The primary structure of the calmodulin-sensitive adenylate cyclase toxin from Bacillus anthracis has been determined from the corresponding nucleotide sequence and compared to that of the homologous toxin secreted by Bordetella pertussis. The cya gene of Bacillus anthracis encodes an 800 amino acid (aa) protein beginning with an N-terminal signal peptide. The central part of the B. anthracis adenylate cyclase includes a region of striking homology with the N-terminal part of the B. pertussis enzyme. In this region a particularly well conserved 24-aa peptide and two other less homologous peptides have been identified. These data corroborate the immunological relatedness of the two enzymes and suggest that the two prokaryotic calmodulin-sensitive adenylate cyclases originate from a common ancestor.

Cloning and expression of the calmodulin-sensitive Bacillus anthracis adenylate cyclase in Escherichia coli

The adenylate cyclase gene of Bacillus anthracis, encoding the edema factor, a component of anthrax toxin, has been cloned and expressed in Escherichia coli. Clones were selected by their capacity to complement the cyclase deficiency (cya-) of an E. coli strain expressing the eukaryotic protein calmodulin, an essential activator of B. anthracis adenylate cyclase. The protein expressed in E. coli was shown to exhibit adenylate cyclase activity only in the presence of calmodulin. Experiments using a coupled in vitro transcription-translation system revealed that the protein synthesized from the cloned DNA fragment was enzymatically active, upon addition of calmodulin, and could be immunoprecipitated by antibodies directed against purified Bordetella pertussis adenylate cyclase toxin. This indicates that the two calmodulin-dependent adenylate cyclase toxins are immunologically related.

Molecular cloning, characterization, and chromosomal localization of dapF, the Escherichia coli gene for diaminopimelate epimerase

The Escherichia coli dapF gene was isolated from a cosmid library as a result of screening for clones overproducing diaminopimelate epimerase. Insertional mutagenesis was performed on the cloned dapF gene with a mini-Mu transposon, leading to chloramphenicol resistance. One of these insertions was transferred onto the chromosome by a double-recombination event, allowing us to obtain a dapF mutant. This mutant accumulated large amounts of LL-diaminopimelate, confirming the blockage in the step catalyzed by the dapF product, but did not require meso-diaminopimelate for growth. The dapF gene was localized in the 85-min region of the E. coli chromosome between cya and uvrD.

Structure of two pectate lyase genes from Erwinia chrysanthemi EC16 and their high-level expression in Escherichia coli

The pelB and pelE genes from Erwinia chrysanthemi EC16, which encode different pectate lyase enzymes, were sequenced and expressed at a high level in Escherichia coli. The genes possessed little similarity to each other in 5' signal regions, signal peptide sequences, coding sequences, or 3' noncoding regions. Both genes contained their own promoters as well as sequences 3' to the coding regions with considerable secondary structure which may function as rho-independent transcriptional termination signals. High-level expression plasmids were constructed with both genes, which led to 20% or more of E. coli cellular protein. The pectate lyases were secreted efficiently to the periplasm and, to a lesser extent, the culture medium. The mature proteins in E. coli periplasmic fractions were obtained in milligram amounts and high purity with a single-column affinity purification method. E. coli cells which produced high amounts of the pelE protein macerated potato tuber tissue as efficiently as E. chrysanthemi EC16 cells but cells producing high amounts of the pelB protein were less effective. Thus, the pelE gene product is an important pathogenicity factor which solely enables E. coli to cause a soft-rot disease on potato tuber tissue under laboratory conditions.

Organization of the adenyl cyclase (cya) locus of Rhizobium meliloti

A cya-like gene encoding adenyl cyclase from Rhizobium meliloti was localized to a 0.8-kb PstI-EcoRI fragment by subcloning experiments. Experiments in Escherichia coli 'maxicells' identified a R. meliloti cya gene product of 28 kDa, which is significantly smaller than the corresponding protein from enteric bacteria. A control region for the expression of the cya gene in E. coli was found on an adjacent 2.6-kb BglII-BamHI sequence by insertional mutagenesis with Tn5 and phage MudI (ApR lac). The direction of transcription of the cya gene was also determined using a cya::MudIlac fusion. Promoter activity of this cya::lac fusion was not decreased when glucose was added to the culture. The R. meliloti cya gene is conserved among R. meliloti strains but no homology could be detected to other Rhizobium species or to E. coli in DNA hybridization experiments.