- Volume 143, Issue 4, 1997
Volume 143, Issue 4, 1997
- Review Article
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- Microbiology Comment
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- Antigens And Immunity
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Antigenic polymorphism of the lipopolysaccharides from human and animal isolates of Bordetella bronchiseptica
More LessSix monoclonal antibodies (mAbs) against lipopolysaccharides (LPS) from Bordetella pertussis (P1P3, 60.5), B. parapertussis (PP2, PP6, PP8) and B. bronchiseptica (BRg1) were used to examine the presence of antigenic determinants of LPS on B. bronchiseptica cells. Forty-eight clinical isolates of this Gram-negative bacterium (4 canine, 3 equine, 6 porcine, 4 rabbit and 31 human) were examined. Significant cross-reactivities with the heterologous anti-pertussis and anti-parapertussis mAbs were observed. The isolates also exhibited marked antigenic polymorphism. The 48 isolates could be classified in six immunogroups. Purified LPS preparations extracted from some isolates were analysed by ELISA, thin-layer chromatography, and tricine-SDS-PAGE. The results show that four main types of antigenic polymorphism of B. bronchiseptica LPSs exist: (a) heterogeneity of the core, (b) presence or absence of O-chains, (c) differences in the hinge region between O-chain and core, and (d) differences in interactions of LPS with other cell-surface constituents. Smooth-type LPS molecules, detectable with mAb PP6, were more frequently observed in animal isolates (94%) than in human isolates (52%). Reverse frequencies were found with mAb 60.5 (48% of human isolates, 18% of animal isolates), which is unable to react with long-chain LPSs. This observation could be due to the general absence of some lectin-like receptor, specific to the O-chain, on human bronchoalveolar tissues.
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- Biochemistry
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Purification of two Bacillus subtilis proteins which cross-react with antibodies directed against eukaryotic protein kinase C, the His HPr kinase and trigger factor
More LessAs in eukaryotes, phosphorylation of Ser and Thr residues in proteins appears to be a common phenomenon in bacteria. Surprisingly, however, very few Ser/Thr protein kinases have been identified and in this study antibodies directed against mammalian protein kinase C (PKC) have been used in attempts to isolate conserved Ser/Thr protein kinases. Using the mAb M7 against rat brain PKC, a single 70 kDa band was identified in total cell extracts of Bacillus subtilis by Western blotting after SDS-PAGE, whilst using polyclonal antibody α-PKC1p against Saccharomyces cerevisiae PKC a single 67 kDa band was identified by the same procedure. The two proteins were purified independently on the basis of antibody recognition employing two-dimensional gel electrophoresis as a final step, which allowed subsequent microsequencing. The 70 kDa band was thus identified as the phosphoenolpyruvate-dependent His HPr kinase, Enzyme I of the phosphotransferase system. This identity was confirmed using a mutant deleted for ptsl, encoding Enzyme I. The 67 kDa protein was identified as a previously unknown B. subtilis ‘trigger factor’, homologous to an Escherichia coli protein-folding enzyme, peptidylprolyl cis-trans-isomerase implicated in cell division.
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Isolation and characterization of the gene encoding single-stranded-DNA-binding protein (SSB) from four marine Shewanella strains that differ in their temperature and pressure optima for growth
More LessThe ssb gene, coding for single-stranded-DNA-binding protein (SSB), was cloned from four marine Shewanella strains that differed in their temperature and pressure optima and ranges of growth. All four Shewanella ssb genes complemented Escherichia coli ssb point and deletion mutants, with efficiencies that varied with temperature and ssb gene source. The Shewanella SSBs are the largest bacterial SSBs identified to date (24.9-26.3 kDa) and may be divided into conserved amino- and carboxy-terminal regions and a highly variable central region. Greater amino acid sequence homology was observed between the Shewanella SSBs as a group (72-87%) than with other bacterial SSBs (52-69%). Analysis of the amino acid composition of the Shewanella SSBs revealed several features that could correlate with pressure or temperature adaptation. SSBs from the three low-temperature-adapted Shewanella strains were an order of magnitude more hydrophilic than that from the mesophilic strain, and differences in the distribution of eight amino acids were identified which could contribute to either the temperature or pressure adaptation of the proteins. The SSBs from all four Shewanella strains were overproduced and partially purified based upon their ability to bind single-stranded DNA. The differences found among the Shewanella SSBs suggest that these proteins will provide a useful system for exploring the adaptation of protein-protein and protein-DNA interactions at low temperature and high pressure.
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Tellurite reductase activity of nitrate reductase is responsible for the basal resistance of Escherichia coli to tellurite
Tellurite and selenate reductase activities were identified in extracts of Escherichia coli. These activities were detected on non-denaturing polyacrylamide gels using an in situ methyl viologen activity-staining technique. The activity bands produced from membrane-protein extracts had the same RF values as those of nitrate reductases (NRs) A and Z. Tellurite and selenate reductase activities were absent from membranes obtained from mutants deleted in NRs A and Z. Further evidence of the tellurite and selenate reductase activities of NR was demonstrated using rocket immunoelectrophoresis analysis, where the tellurite and selenate reductase activities corresponded to the precipitation arc of NR. Additionally, hypersensitivity to potassium tellurite was observed under aerobic growth conditions in nar mutants. The tac promoter expression of NR A resulted in elevated tellurite resistance. The data obtained also imply that a minimal threshold level of NR A is required to increase resistance. Under anaerobic growth conditions additional tellurite reductase activity was identified in the soluble fraction on non-denaturing gels. Nitrate reductase mutants were not hypersensitive under anaerobic conditions, possibly due to the presence of this additional reductase activity.
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- Biotechnology
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Chemical characterization and spectroscopic analysis of the solubilization products from wheat straw produced by Streptomyces strains grown in solid-state fermentation
The effects of two extraction procedures on the yield and properties of APPL (acid-preciμltable polymeric lignin, or solubilized lignocellulose) produced by four streptomycetes during growth in solid-state fermentation were examined. When APPL was extracted with NaOH (0.1 M) rather than distilled water, yields increased threefold, with Streptomyces chattanoogensis exhibiting maximum solubilization levels [163 mg product (g straw)-1]. Alterations in the characteristics of APPL obtained during extraction with NaOH were detected using cross-polarization and magic-angle sμlnning (CPMAS) 13C NMR and IR spectroscopy and by GC-MS analysis after CuO oxidation, with the most significant changes detected in the cinnamic acid and lignin moieties. When APPL was extracted with NaOH, ester links between hemicellulose and lignin and between hemicellulose and cinnamic acid were cleaved, resulting in a decrease in the alkyl and carbonyl groups attached to lignin, enabling greater solubilization. Yields of APPL extracted with water were lower, but spectral characterization of this APPL suggested a possible role for actinomycete peroxidases and phenolic acid esterases in lignin solubilization. For industrial solubilization of lignocellulose, a possible role for the application of streptomycetes, or their enzymes, in alkali extraction is suggested as a means of increasing solubilization levels.
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- Development And Structure
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Membrane topology analysis of the Bacillus subtilis BofA protein involved in pro-σ K processing
More LessThe Bacillus subtilis BofA protein is involved in regulation of pro-σ K processing in the mother cell during the late stages of sporulation. A computer analysis of the BofA amino acid sequence indicates that it is an integral membrane protein. To determine the membrane topology of the protein, a series of gene fusions of bofA with lacZ or phoA reporter genes in Escherichia coli were analysed. A BofA topological model with two membrane-spanning segments, and with the N- and the C-terminal domains located in the region between the inner and outer membranes surrounding the forespore is presented. The analysis of different modifications of the last five amino acid residues of the BofA protein, obtained by PCR site-directed mutagenesis, suggests a possible role of the C-terminal domain in the regulation of pro-σ K processing.
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Contact with a solid substratum induces cysts in axenic cultures ofPhysarum polycephalum amoebae: mannitol-induced detergent-resistant cells are not true cysts
More LessPrevious workers reported thatPhysarum polycephalum amoebae cultured in liquid axenic medium were induced to form cysts by the addition of mannitol. Their criterion for encystment was the formation of detergent (Triton)-resistant cells (TRC). In this study the frequencies of TRC in suspensions of amoebae from various treatments were compared with counts of cell types identified by transmission electron microscopy. Amoebae treated with mannitol in axenic liquid culture formed 50% TRC after 17 h but no walled cysts were found. It was concluded that TRC induced by mannitol were dense, rounded cells without walls. In contrast, TRC formed after growth to stationary phase on bacterial lawns were walled cells. When resuspended in growth medium, most mannitol-induced TRC reverted to active amoebae within a few minutes, whereas TRC formed on bacteria remained Triton resistant for many hours. It was concluded that delayed reversion of TRC was a more reliable indication of wall formation than Triton resistance alone. Transfer of amoebae from liquid culture to the surface of diluted axenic agar medium resulted in the formation of walled cysts identical in appearance with those formed on bacterial lawns. The results indicated that efficient encystment requires a solid substratum as well as nutrient deprivation.
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- Genetics And Molecular Biology
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Characterization of genes for the biosynthesis of the compatible solute ectoine from Marinococcus halophilus and osmoregulated expression in Escherichia coli
More LessThe genes of the biosynthetic pathway of ectoine (1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid) from the Gram-positive moderate halophile Marinococcus halophilus were cloned by functional expression in Escherichia coli. These genes were not only expressed, but also osmoregulated in E. coli, as demonstrated by increasing cytoplasmic ectoine concentration in response to medium salinity. Sequencing of a 4∙4 kb fragment revealed four major ORFs, which were designated ectA, ectB, ectC and orfA. The significance of three of these genes for ectoine synthesis was proved by sequence comparison with known proteins and by physiological experiments. Several deletion derivatives of the sequenced fragment were introduced into E. coli and the resulting clones were investigated for their ability to synthesize ectoine or one of the intermediates in its biosynthetic pathway. It was demonstrated that ectA codes for l -2,4-diaminobutyric acid acetyltransferase, ectB for l -2,4-diaminobutyric acid transaminase and ectC for l -ectoine synthase. A DNA region upstream of ectA was shown to be necessary for the regulated expression of ectoine synthesis in response to the osmolarity of the medium.
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Copper-inducible transcriptional regulation at two promoters in the Escherichia coli copper resistance determinant pco
More LessThe pco determinant of Escherichia coli plasmid pRJ1004 encodes inducible resistance to the trace element copper. The identification of two copper-dependent transcriptional initiation regions within pco that each contain a similar upstream hyphenated dyad motif is described. Deletion constructs showed that this “copper box” motif was essential for copper-inducible activity at both pco promoters, PpcoA and PpcoE. The placement of the motif differs in the two promoters, and PpcoA contains an extended -10 nonamer typical of promoters for which RNA polymerase does not bind specifically to -35 sequences. PpcoE does not contain this motif and is the more strongly expressed promoter. The transcript from PpcoA contains the pcoABCDRS genes, while PpcoE expresses only pcoE. The induction profiles for PpcoA- and PpcoE-lacZ fusions were flattened sigmoidal curves with a gradual response to increasing copper concentration. On high-copy-number plasmids, zinc was found also to induce transcription from both promoters in vivo. Both promoters showed inducible activity in the absence of pcoRS, the plasmid-borne two-component regulatory system, indicating that a second trans-acting regulatory system is present on the chromosome. The pcoR product showed repressor action in the absence of pcoS, while still allowing induction, suggesting the chromosome encoded a similar two-component system to pco. TnphoA insertion mutagenesis identified chromosomal genes which affected promoter expression, including ptsH, ptsl (sugar phosphotransferase system) and cya (adenylate cyclase). The results support that idea that pco-encoded copper resistance is an auxiliary mechanism for handling copper, the regulation of which is integrated with the chromosomal regulation of cellular copper metabolism.
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Expression of a Butyrivibrio fibrisolvens E14 gene (cinB) encoding an enzyme with cinnamoyl ester hydrolase activity is negatively regulated by the product of an adjacent gene (cinR)
More LessA second cinnamoyl ester hydrolase (CEH) encoding gene (cinB) has been characterized from the ruminal bacterium Butyrivibrio fibrisolvens E14. CinB is more similar to CinA (previously named Cinl) (28% amino acid identity), the first CEH described from B. fibrisolvens E14, than either of the enzymes are to any other member of the family of hydrolases to which they belong. Upstream of cinB, and in the opposite orientation, is a gene (cinR) encoding a protein with substantial similarity to members of the MarR family of negative regulators of bacterial gene expression. By alignment of these sequences, a possible helix-turn-helix DNA-binding domain has been identified. CinR was expressed at a high level in Escherichia coli using the lac promoter. In E. coli CinR repressed the expression of CinB, but had no effect on the expression of CinA. In gel mobility-shift assays, CinR bound specifically to the cinR-cinB intergenic region. Two identical 16 nucleotide inverted repeats adjacent to the putative PcinR and PcinB promoters are likely binding sites for CinR. The addition of FAXX (O-[5-O-(trans-feruloyl)-α-L-arabinofuranosyl]-(1,3)-O-ß-D-xylopyranosyl-(1,4)-D-xylopyranose) and Fara [5-O-(trans-feruloyl)-arabinofuranose], but not xylobiose, ferulic acid and a number of other soluble components of hemicellulose, inhibited the binding of CinR to DNA.
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Characterization and overexpression of the Aspergillus niger gene encoding the cAMP-dependent protein kinase catalytic subunit
More LessThe gene pkaC encoding the catalytic subunit of cAMP-dependent protein kinase has been isolated from the industrially important filamentous fungus Aspergillus niger. A probe for screening A. niger phage libraries was generated by a polymerase chain reaction using degenerate primers. cDNA and genomic DNA clones were isolated and sequenced. An open reading frame of 1440 bp, interrupted by three short introns, encodes a polypeptide of 480 amino acids with a calculated molecular mass of 53813 Da. The cAMP-dependent protein kinase catalytic subunit (PKA-C) from A. niger has a 126 amino acid extension at the N-terminus compared to the PKA-C of higher eukaryotes that - except for the first 15 amino acids, which are homologous to the Magnaporthe grisea PKA-C - shows no significant similarity to the N-terminal extension of PKA-C of other lower eukaryotes. The catalytic core of PKA-C of A. niger shows extensive homology with the PKA-C isolated from all other eukaryotes. Low-stringency hybridization did not reveal any other pkaC homologue in A. niger. The cloned pkaC was used for transformation of A. niger, leading to increased levels of pkaC mRNA and PKA-C activity. Transformants overexpressing pkaC were phenotypically different with respect to growth, showing a more compact colony morphology, accompanied by a more dense sporulation, especially on media containing trehalose and glycerol. A number of transformants also showed a strongly reduced or complete absence of sporulation. This phenotype was quickly lost upon propagation of the strains.
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A carboxy-terminal processing protease gene is located immediately upstream of the invasion-associated locus from Bartonella bacilliformis
More LessA gene with homology to those encoding an unusual class of C-terminal processing proteases that flanks the invasion-associated locus iaIAB of Bartonella bacilliformis has been identified. The 1302 bp gene, termed ctpA, is located immediately upstream of the ialA gene and encodes a predicted nascent product of 434 amino acids, producing a mature protein of 411 amino acid residues. The Bartonella CtpA appears to undergo autolysis in vitro, producing multiple products of 43-46 kDa, and a second group of products of 36-37 kDa. Production of CtpA in vivo gives a single product of 41.8 kDa. In addition to a computer-predicted N-terminal secretory signal sequence, the molecular mass difference in vivo versus in vitro indicates that CtpA is likely to be secreted and post-translationally modified. The full-length CtpA protein shows 30% identity to the CtpA protein of Synechocystis sp. 6803 (69% overall sequence similarity). The mature CtpA protein also has significant homology to the tail-specific protease (Tsp) of Escherichia coli, with 22% identity and 62% similarity to an internal region of the 660 amino acid Tsp. The CtpA protein does not appear to exhibit haemolysin, collagenase, or caseinase activity. The ctpA gene is conserved in all Bartonella species examined, as determined by hybridization analyses, but it was not found in Brucella abortus or E. coli. The ctpA gene does not directly affect the erythrocyte-invasion phenotype conferred by iaIAB, but its homology to other stress-response processing proteases implies an important role in survival of this intracellular pathogen.
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Squalene-hopene cyclase from Bradyrhizobium japonicum: cloning, expression, sequence analysis and comparison to other triterpenoid cyclases
More LessWith the help of a PCR-based screening method, the gene encoding squalene-hopene cyclase (SHC) of Bradyrhizobium japonicum USDA 110 was isolated from a cosmid library. The SHC catalyses the cyclization of squalene to hopanoids, a class of triterpenoid lipids recently discovered in nitrogen-fixing, root-nodule-forming Bradyrhizobium bacteria. Hybridization experiments showed that the gene is present in bacteria of all Bradyrhizobium strains tested and in photosynthetic bacteria forming stem nodules on tropical legumes of the genus Aeschynomene. The Bradyrhizobium shc gene is 1983 bp in length and encodes a protein of 660 amino acid residues with a calculated molecular mass of 73671 Da. Comparison of the deduced amino acid sequence with the sequences of other SHCs revealed highest similarity (70%) to the SHC from the Gram-negative Zymomonas mobilis and lower similarity (48%) to the SHCs from the Gram-positive Alicyclobacillus acidocaldarius and Alicyclobacillus acidoterrestris. Bradyrhizobium SHC also showed similarity (38-43%) to eukaryotic oxidosqualene cyclases. The B. japonicum shc gene was expressed in Escherichia coli. The recombinant SHC catalysed the cyclization of squalene to the hopanoids hopene and diplopterol in vitro. However, the formation of the gammacerane derivative tetrahymanol, which is produced in addition to hopanoids in B. japonicum strains in vivo, could not be detected in vitro. Therefore, the presence of a second squalene cyclase in B. japonicum can be assumed. Sequence analysis of 0.5 kb upstream from the shc gene identified a partial ORF with significant similarity to the C-terminus of an ORF located immediately upstream from the shc gene in Z. mobilis. Both ORFs also showed similarity to phytoene desaturases from cyanobacteria and plants. The 3'-end of this ORF from B. japonicum overlaps with 13 bp at the 5'-end of shc. The close proximity of this ORF to shc suggests that shc and this ORF may be part of an operon.
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Identification of genes in Rhizobium leguminosarum bv. trifolii whose products are homologues to a family of ATP-binding proteins
More LessThe wild-type Streptomyces lividans 66 genome contains a 4.3 kb amplifiable DNA unit (AUD), and its four ORFs encode proteins that could not be identified by sequence comparison with databases. One of the gene products (encoded by orf-2) was purified and determined to be a novel 23 kDa protein. This protein is synthesized by the wild-type strain, absent in a variant lacking the AUD and overproduced in a variant in which the AUD is amplified (ADS). Immunological studies and analyses by confocal laser microscopy showed that the 23 kDa protein is associated with the substrate hyphae of the wild-type and the ADS-containing variant. Examination by microscopy revealed that the strain carrying the ADS forms bulges within the substrate hyphae and apical vesicles. These bulges have high levels of associated 23 kDa protein and contain storage-like material.
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Use of an excision reporter plasmid to study the intracellular mobility of the conjugative transposon Tn916 in Gram-positive bacteria
More LessAn excision reporter plasmid was constructed to characterize the intracellular mobility of Tn916 in various Gram-positive bacteria. The reporter component of this plasmid is a chloramphenicol-resistance gene which has been insertionally inactivated with the integrative vector pAT112 containing the attachment site of Tn916. Tn916-mediated excision of pAT112, to produce clones resistant to chloramphenicol, was detected in Enterococcus faecalis BM4110, Listeria monocytogenes L028-Str and Streptococcus gordonii BM120, but not in Lactococcus lactis MG1363-RF or in Streptococcus pneumoniae BM124, and always depended upon the ability of the bacterial host to generate circular forms of the transposon. The results suggest that (i) the excision event, although required, is not sufficient for conjugal transfer to occur and (ii) there is no linear relationship between the donor potential of E. faecalis strains and either the excision frequency of pAT112 or the copy number of Tn916 circular intermediates per cell in these hosts. Excision of pAT112 occurred mainly during the late exponential phase of growth of E. faecalis and L. monocytogenes and this recombination event was not stimulated by heat shock, salt and alcohol stresses or by the presence of tetracycline in the medium.
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The TBP gene from Aspergillus nidulans -structure and expression in Saccharomyces cerevisiae
More LessThe genomic and cDNA copy of the TATA-binding protein (TBP) gene from the filamentous fungus Aspergillus nidulans have been cloned. The gene is interrupted by four introns, one of which is in the long 5' untranslated region of 615 bp. The transcription initiation site was established and the levels of mRNA were analysed under diverse growth conditions and found to vary severalfold. The gene encodes a protein of 268 amino acids composed of an N-terminal domain of 88 amino acids with no significant homology to other TBPs and a C-terminal domain of 180 amino acids with about 95% homology to other fungal TBPs. A cDNA clone under the yeast ADH1 promoter was able to substitute for the yeast TBP gene in vivo; however, the transformants obtained grew poorly at 35°C and on galactose and glycerol at 30°C, though they could grow in the presence of copper ions or aminotriazole at this temperature. This phenotype may be the result of altered function of A. nidulans TBP in certain yeast transcription activation pathways.
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Genes encoding the NAD-reducing hydrogenase ofRhodococcus opacus MR11
More LessThe dissociation of the soluble NAD-reducing hydrogenase of Rhodococcus opacus MR11 into two dimeric proteins with different catalytic activities and cofactor composition is unique among the NAD-reducing hydrogenases studied so far. The genes of the soluble hydrogenase were localized on a 7.4 kbp AsnI fragment of the linear plasmid pHG201 via heterologous hybridization. Analysis of the nucleotide sequence of this fragment revealed the seven open reading frames ORF1, hox F, -U, -Y, -H, -W and ORF7. The six latter ORFs belong to the gene cluster of the soluble hydrogenase. Their gene products are highly homologous to those of the NAD-reducing enzyme of Alcaligenes eutrophus H16. The genes hox F, -U, -Y and -H encode the subunits α, γ, δ and ß, respectively. The gene hoxW encodes a putative protease, which may be essential for C-terminal processing of the ß subunit. Finally, ORF7 encodes a protein which has similarities to cAMP- and cGMP-binding protein kinases, but its function is not known. 0RF1, which lies upstream of the hydrogenase gene cluster, encodes a putative transposase found in IS elements of other bacteria. Northern hybridizations and primer extensions using total RNA of autotrophically and heterotrophically grown cells of R. opacus MR11 indicated that the hydrogenase genes are under control of a α70-like promoter located at the right end of ORF1 and are even transcribed under heterotrophic conditions at a low level. Furthermore, this promoter was shown to be active in the recombinant Escherichia coli strain LHY1 harbouring the 7.4 kbp AsnI fragment, resulting in overexpression of the hydrogenase genes. Although all four subunits of the soluble hydrogenase were shown via Western immunoblots to be synthesized in E. coli, no active enzyme was detectable.
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Structure and gene-polypeptide relationships of the region encoding glycerol diffusion facilitator (glpF) and glycerol kinase (glpk) of Pseudomonas aeruginosa
More LessThe glycerol facilitator is one of the few known examples of bacterial solute transport proteins that catalyse facilitated diffusion across the cytoplasmic membrane. A second protein, glycerol kinase, is involved in entry of external glycerol into cellular metabolism by trapping glycerol in the cytoplasm as sn-glycerol 3-phosphate. Evidence is presented that glycerol transport in Pseudomonas aeruginosa is mediated by a similar transport system. The genes encoding the glycerol facilitator, glpF, and glycerol kinase, glpK, were isolated on a 4.5 kb EcoRI fragment from a chromosomal mini-library by functional complementation of an Escherichia coli glpK mutant after establishing a map of the chromosomal glpFK region with the help of a PCR-amplified glpK segment. The nucleotide sequence revealed that glpF is the promoter-proximal gene of the glpFK operon. The glycerol facilitator and glycerol kinase were identified in a T7 expression system as proteins with apparent molecular masses of 25 and 56 kDa, respectively. The identities of the glycerol facilitator and glycerol kinase amino acid sequences with their counterparts from Escherichia coli were 70 and 81%, respectively; this similarity extended to two homologues in the genome sequence of Haemophilus influenzae. A chromosomal δglpFK mutant was isolated by gene replacement. This mutant no longer transported glycerol and could no longer utilize it as sole carbon and energy source. Two ORFs, orfX and orfY, encoding a putative regulatory protein and a carbohydrate kinase of unknown function, were located upstream of the glpFK operon.
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