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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Both ATP and an electrochemical potential play roles in translocating proteins across the Inner membrane of Escherichia coli. Recent discoveries have dissected the overall transmembrane movement into separate subreactions with different energy requirements, identified a translocation ATPase, and reconstituted both energy-requiring steps of the reaction from purified components. A more refined understanding of the energetics of this fundamental process is beginning to provide answers about the basic issues of how proteins move across the hydrophobic membrane barrier.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Regulation of transcription occurs at different levels, one being in the presence of sequences specifically recognized by different forms of RNA polymerase, i.e. the promoters. Three different kinds of promoter are defined according, among other things, to their dependence on the growth rate of the cell: the house-keeper' promoter of many metabolic genes, the stringent promoter found at several rRNA and ribosomal protein genes, and the ‘gearbox’ at genes whose products are required at higher relative amounts at lower growth rates. The identified gearbox promoters of Escherichia coli share specific homologies in the -10, -35 and upstream regions. Although there may be different types of gearbox promoters, the -10 sequence of one of these promoters has been found to be essential for functioning as a gearbox. This suggests the existence of specific sigma factors for its transcription. RpoS (KatF) is a likely candidate for being one of these sigma factors. Computer simulation allows us to predict that such sigma factors should, in turn, be expressed following a gearbox mode, which would then imply the existence of self-regulated loops contributing to the expression of some genes of bacterial division. Some bacterial gene products need to be synthesized al fixed amounts per cell
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Many species within the order Actinomycetales contain one or more soluble cytochrome P450 monooxygenases, often substrate-inducible and responsible for a variety of xenobiotic transformations. The individual cytochromes exhibit a relatively broad substrate specificity, and some strains have the capacity to synthesize large amounts of the protein(s) to compensate for low catalytic turnover with some substrates. All three of the Streptomyces cytochromes sequenced to date are exclusive members of one P450 family, CYP105. In several instances, monooxygenase activity arises from induction of a P450 and associated ferredoxin, or of a P450 only, suggesting that some essential electron donor proteins (reductase and ferredoxin) are not coordinately regulated with the cytochrome. The overall properties of these systems suggest an adaptive strategy whose twofold purpose is to maintain a competitive advantage via the production of secondary metabolites, and, whenever possible, to utilize unusual growth substrates by introducing metabolites from these reactions into the more substrate-specific primary metabolic pathways.
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  • 4
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Electrotransformation of Rhodococcus fascians by non-replicating plasmids containing a suitable resistance marker resulted in stable transformants by integration of these constructs at various sites in the genome, thereby generating different mutations. Tagged genes could be isolated in Escherichia coli owing to the presence of a CoIE1 replicon and an ampicillin resistance gene in the inserted sequences.Southern analysis and nucleotide sequencing revealed that recombination can occur at defined locations in the plasmid, while no site preference for target sequences could be detected. Low homology between the recombining sequences indicates illegitimate recombination. The specificity of the plasmid sites could be explained by assuming a linear recombination intermediate, generated by cleavage of the transformed plasmid.
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  • 5
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Translational fusions between a mutant phoA (lacking its promoter, ribosomal binding site and signal peptide sequence) and Rhizobium‘symbiotic’ genes were isolated. Since these fusions expressed alkaline phosphatase (AP), the product of phoA, the genes into which phoA was inserted apparently specify proteins located in the bacterial periplasm or cell membrane, the compartment in which AP has activity. These genes were psiA and genes upstream of psiA (psiA is required for normal nodule development and strains with multicopy psiA fall to make exopolysaccharide (EPS) and to nodulate). Fusions between phoA and pss (exo) genes, which are required for EPS production, also resulted in the expression of AP indicating that products of these pss genes were located at the cell surface. Using grus fusions to psiA and pssA, we found that the former was expressed in N2-fixing bean root nodules but the latter was not.
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  • 6
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The extracellularly secreted endopeptidase elastase (LasB) is regarded as an important virulence factor of Pseudomonas aeruginosa. It has also been implicated in the processing of LasA which enhances elastolytic activity of LasB. In order to Investigate the role of LasB in virulence and LasA processing, a LasB-negative mutant, PA01E, was constructed by insertional mutagenesis of the LasB structural gene, lasB, in P. aeruginosa PAO. An Internal 636 bp lasB fragment of the plasmid pRB1803 was ligated into a derivative of the mobilization vector pSUP201–1. The resulting plasmid, pBRMOB-LasB, was transformed into Escherichia coli and transferred by filter matings to the LasB-positive P. aeruginosa strain, PA01. Plasmid integration in the lasB site of the chromosome was confirmed by Southern blot analysis. Radioimmunoassay and immunoblotting of PA01E supernatant fluids yielded no detectable LasB (〈1 ng ml-1 LasB). The absence of LasB in PA01E was further proven by the inability of its culture supernatant fluid to cleave transferrin or rabbit immunogiobulin G (IgG) after a 72 h incubation. The residual proteolytic activity of PA01E culture supernatant fluid was attributed to alkaline proteinase (Apr), since it was totally inhibited by specific antibodies against Apr. Residual elastolytic activity in culture supernatant fluid of PAO1E was due to the LasA fragment and to the combined action of the LasA fragment with Apr on elastin. The sizes of purified LasA from PA01 and PA01E were identical (22 kDa). These results show that, besides LasB and the LasA fragment, Apr may also act on elastin in the presence of the LasA fragment and that the proteolytic processing of LasA in P. aeruginosa is independent of LasB.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: An invasive Escherichia coli (EIEC) isolate was found to bind basement-membrane laminin in a saturable and time-dependent manner. Excess of unlabelled laminin inhibited the binding of the radioactively labelled protein. Non-invasive E. coli K-12 exhibited only low-level laminin binding but introduction of the virulence-associated plasmid from the EIEC isolate led to high-level binding. Expression of a receptor for laminin on the bacteria was therefore associated with the presence of the virulence plasmid. Scatchard plot analysis Indicated approximately 1000 receptors per bacterial cell, and a Kd of high-affinity binding of 0.5 pM. A laminin-binding protein which correlated with the presence of the plasmid was isolated and characterized. Its sequence of the eight amino-terminal amino acids was identical to that of the LamB protein of E. coli, although the molecular mass of the two in sodium dodecyl sulphate/polyacrylamide gel (SDS-PAGE) appeared to be slightly different. Both proteins reacted in immunoblot assays with polyclonal antisera raised against either protein, and both proteins bound laminin. Southern-blot hybridization analysis established that both the EIEC strain and the K-12 strains with or without the virulence plasmid contained one lamB gene only, and no laminin-binding protein appeared when the virulence plasmid was introduced into bacteria deleted for the lamB gene. On the basis of these results we suggest that native LamB protein of E. coli or a modified variant of it serves as a major receptor for laminin binding and is present at an increased level in invasive E. coli containing the virulence plasmid.
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  • 8
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We describe here the cloning, characterization and analysis of the regulation of the ARO2 gene of Saccharomyces cerevisiae, the first reported study of a eukaryotic gene encoding chorismate synthase (E.C. 4.6.1.4). The gene contains an ORF of 1128 bp, encoding a protein with a calculated molecular mass of 40.8 kDa. ARO2 is regulated under the ‘general control system’ for amino acid biosynthesis by the transcriptional activator GCN4 which binds in vitro at three sites within the AR02 promoter.The AR02 gene product is highly similar to its Escherichia coli counterpart, with a 47% identity distributed over the entire length of the peptide. We therefore suggest that the S. cerevisiae chorismate synthase, in contrast to the Neurospora crassa enzyme, but like other chorismate synthases, is a monofunctional peptide, solely possessing chorismate synthase activity.
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  • 9
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Bacillus subtilis cell extracts, prepared at different times during growth, contained several proteins that were apparently guanylylated in vitro with [α-32P]-GTP. Four of the proteins were partially purified and the N-terminal amino acid sequences (13 to 20 residues) were determined. One sequence had 84% identity to Bacillus stearothermophlius triosephosphate isomerase, two were 100% identical to the predicted sequences of the B. subtilis ptsI and ptsH genes while no identity was found for the fourth sequence. This apparent guanylylation occurred with proteins involved in glucose metabolism, although the significance is unknown.
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  • 10
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The gene ntcA is required for full expression of proteins subject to ammonium repression in the cyanobacterium Synechococcus. A 3.1 kb DNA fragment able to complement an ntcA mutant was digested with exonuclease III, and deleted fragments of different sizes were tested for complementation of that mutant, allowing the localization of its mutation within a BamHI-HindIII genomic fragment of c. 0.4 kb. Insertion of a chloramphenicol-resistance-encoding gene cassette into both the BamHI and the HindiIII sites of wild-type Synechococcus resulted in a pleiotropic, nitrogen-assimilation-minus phenotype, corroborating the presence of the ntcA gene in that genomic region. Sequencing of DNA in this region showed the presence of an open reading frame that included both the BamHI and the HindIII sites. The ntcA gene product, NtcA, is a protein of 24817 Da which belongs to a family of bacterial transcriptional activators that, among others, includes Crp and Fnr from Escherichia coli. Of special biological significance, it appears, is the presence of a conserved helix-turn-helix motif in the sequence close to the C-terminal end of all the proteins in the family. The gene ntcA is proposed to encode a transcriptional activator of genes subject to nitrogen control in Synechococcus.
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