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  • 1990-1994  (93,521)
  • 1970-1974  (1)
  • 1955-1959  (1)
  • 1990  (93,521)
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  • 1
    facet.materialart.
    Unknown
    Totowa, NJ : Humana Press
    Keywords: Molecular Biology / methods
    Notes: This is a series title, single volumes see link below.
    ISSN: 1940-6029
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  • 2
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    New York, NY : Elsevier
    Keywords: Biochemistry ; Enzymes
    Notes: This is a series title, single volumes see link below.
    ISSN: 1557-7988
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  • 3
    Keywords: Leukemia / therapy ; Prognosis
    Notes: Last volumes with varying subtitle and editor.
    ISSN: 0949-7021
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  • 4
    Keywords: Hazardous Substances / toxicity
    Notes: Ceased with vol. 15(1999).
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  • 5
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    Unknown
    Königswinter : Petersberg Verlag
    Keywords: Arbeitsgemeinschaft der Großforschungseinrichtungen (Germany) ; Research institutes / Germany ; Research ; Germany
    Notes: Ceased with ed. 1995.
    ISSN: 0935-2236
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 6 (1990), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: Allen gives an algebra for representing qualitative temporal information about the relationships between pairs of intervals. In this paper, we address a fundamental reasoning task that arises in applications of the algebra: Given (possibly indefinite) knowledge about the relationships between intervals, find all feasible relationships between two intervals. We call this the minimal labels problem. Finding the minimal labels can be viewed as computing the deductive consequences of our knowledge. Determining exact solutions to this problem has been shown to be (almost assuredly) intractable. Allen gives an approximation algorithm based on constraint propagation. We present new approximation algorithms; determine analytically under what conditions the algorithms are exact; and examine, through some computational experiments, the quality of the approximate solutions produced by the algorithms. We also give a simple test for predicting when the approximation algorithms will and will not produce good quality approximations. Finally, we survey three example applications of the interval algebra chosen from the literature to show where the results of this paper could be useful.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 6 (1990), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: In this paper, we present a formalism called feature grammar and its application to several problems of semantic analysis. Our extension concerns the structure of the feature value sets, which can be complex, and the definition of unification, which is dependent on this structure. Moreover, we introduce generation rules for feature symbols in order to determine well-formed symbols, which form the alphabet of a formal language for natural language analysis.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 12 (1990), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Notes: The conventional approach for introducing statistics to beginning students is to start with descriptive measures such as histograms, means and standard deviations, followed by other technical notions. The problem of such an approach is lack of motivation. It is useful to introduce students, at an early stage, to an overview of the statistical approach used to obtain the desired information. Accordingly, schematic models for the purpose of introducing two fundamental designs for statistical investigation are presented in this article.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 12 (1990), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 12 (1990), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
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  • 11
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 12 (1990), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Notes: Exploratory date analysis provides powerful numerical and graphical tools with which to summarise and interpret data. In this article the authors describe their work with students who were given the opportunity to engage in the solution of a real problem in the physics laboratory which requried statistical techniques.
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  • 12
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 12 (1990), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Notes: In a recent article in Teaching Statistics, Marcuson (1989) has presented an interesting alternative approach to establishing some combinatorial identities, quite different from the usual induction proofs. The purpose of this short note is to suggest yet another way in whcih combinatorics can sometimes be approached.
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  • 13
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 12 (1990), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
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  • 14
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 12 (1990), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 12 (1990), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Notes: Books Reviewed in this Article:Facts and Figures: A practical approach to Statistics By David Baker. Stanley Thornes. 1989.Statistical Reasoning in Law and Public Policy: Volume 1, Statistical Concepts and Issues of Fairness By Joseph L. Gastwirth.Data Handling Skills in G.C.S.E. Science By Ian Pritchard.
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  • 16
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 12 (1990), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
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  • 17
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Physics, Section B 342 (1990), S. 1-14 
    ISSN: 0550-3213
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Nucleotide sequence analysis of a Ureaplasma urealyticum DNA fragment, homologous to cloned urease genes of other prokaryotes, revealed three consecutive open reading frames. The molecular weights of the three deduced polypeptides are 11.2kD, 13.6kD and 66.6 kD. These values are consistent with the size of the three subunits previously reported for purified native urease. A significant sequence homology was found between the three polypeptides of the ureaplasmal urease and the single polypeptide of jack bean (Canavalia ensiformis) urease. Codon usage indicates that UGA is a tryptophan codon in this mollicute. Use of polymerase chain reactions has disclosed the existence of genetic polymorphism among the urease genes of different serotypes of U. urealyticum.
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  • 19
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The budding yeast Saccharomyces cerevisiae has a limited life span, defined by the number of times an individual cell divides. Longevity in this organism involves a genetic component. Several morphological and physiological changes are associated with yeast aging and senescence. One of these, an increase in generation time with age, provides a ‘biomarker’ for the aging process. This increase in generation time has revealed the operation of a ‘ senescence factor(s)’, which is likely to be a product of age-specific gene expression. The Cell Spiral Model indicates coordination of successive cell cycles to be inherent in the determination of life span. It is proposed that life expectancy depends on the function of a stochastic trigger during aging that sets in motion a programme leading to cell senescence and death.
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  • 20
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Using a variety of mutagenic methods, we have generated a series of ciprofloxacin-resistant mutants derived from Escherichia coli strains which overproduce the DNA gyrase A protein. Many of these mutants are found to overexpress a 60 kD protein which is shown to be highly homologous in terms of N-terminal a mi no acid sequence to the E. coli heat-shock protein, GroEL. Other evidence confirms that the 60 kD protein is unrelated to DNA gyrase and is similar, but not identical, to GroEL.
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  • 21
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The nucleotide sequence of a 5082bp fragment of chromosomal DNA from Klebsiella pneumoniae strain UNF5023 is reported. The sequence includes the last four genes of an operon of genes specifically required for the secretion of the enzyme pullulanase. All four genes (puIL, puIM, puIN and puIO) are shown to be required for pullulanase secretion, as is a fifth gene (puIK) which extends beyond the 5′ end of the sequenced DNA. The products of the puIL, puIM, puIN and puIO genes (44kD, 18kD, 27kD and 24kD, respectively) are all predicted to have one or more hydrophobic domains typical of signal sequences and/or membrane anchors, and were all found mainly associated with the inner membranes of subfractionated cells in which the corresponding genes had been expressed from the bacteriophage T7 gene 10 promoter. The results of this study increase the number of genes which have been identified as required for pullulanase secretion to eight, in addition to genes coding for components of the general export pathway.
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  • 22
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The act gene of Escherichia coli encodes the pyruvate formate-lyase-activating enzyme which is necessary for the post-translational modification of pyruvate formate-lyase. The gene is located 191 bp downstream from the pfl structural gene. Northern blot analysis revealed that the act transcript is monocistronic and that transcription is independent of pfl gene expression. Through mapping of the 5′ and 3′ ends of the act transcript, sequences could be identified showing similarity to both an Escherichia coliσ70 promoter and to a rho-independent transcription terminator. Expression of the act gene was analysed with the aid of chromosomally integrated transcriptional and translational lacZ fusions. The results verified that the act gene is transcribed from its own promoter and that expression of the gene is essentially constitutive. Anaerobiosis led only to a two-fold increase in expression over that observed in aerobically grown cells and this elevated expression was independent of the transcriptional regulator, Fnr. Moreover, effectors such as pyruvate and nitrate, which substantially influence anaerobic transcription of the pfl gene, did not affect act gene expression.
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  • 23
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The de novo purine biosynthetic enzymes 5-amino-4-imidazolecarboxamide-ribonucleotide (AICAR) transformylase (EC 2.1.2.3), IMP cyclohydrolase (EC 3.5.4.10) and glycineamide-ribonucleotide (GAR) synthetase (EC 2.1.2.2) are encoded by the purHD locus of Escherichia coli. The DNA sequence of this locus revealed two open reading frames encoding polypeptides of Mr57335 and 45945 (GAR synthetase), respectively, that formed an operon. The DNA sequence, maxicell and complementation analyses all supported the concept that the Mr 57335 polypeptide is the product of the purH gene and encodes a bifunctional protein containing both AICAR trans-formylase and IMP cyclohydrolase activities. The 5′ end of the purHD mRNA was determined by primer extension mapping and contains two regions of dyad symmetry capable of forming ‘hairpin’ loops where the formation of the one would prevent the formation of the other but not vice versa. Regulation by the purR gene product was explained by the discovery of a purR binding site in the purHD control region.
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  • 24
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The sequence of the coagulase gene (coa) from Staphylococcus aureus strain 8325-4 is reported. The deduced amino acid sequence of the coagulase protein is compared with previously reported sequences of coagulases from strains 213 and BB. The secreted mature forms of coagulase proteins are composed of three distinct segments: (i) the N-terminal 150–270 residues, which are c. 50% identical, (ii) a central region with high (〉90%) residue identities, and (iii) a C-terminal region composed of repeated 27-amino-acid residue sequences. The variable N-terminal sequences are probably responsible for antigenic differences among coagulases of different serotype. The region of coagulase which binds to prothrombin and activates it to form staphylothrombin is also located in the N-terminal half of the protein.A site-specific substitution mutation in the coa gene, which abolished plasma clotting activity, was isolated by recombinational allele-replacement in strains 8325-4 and M60. The Coa− mutants did not show diminished virulence in subcutaneous and intramammary infections of mice. No evidence for a role for coagulase in virulence of toxigenic or non-toxigenic strains was obtained. This contradicts findings of several groups using Coa− mutants generated by chemical mutagenesis and suggests that the earlier results were obtained with strains that had suffered additional mutations in virulence-related genes.
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  • 25
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The mechanism by which N-ethylmaleimide (NEM) elicits potassium efflux from Escherichia coli has been investigated. The critical factor is the formation of specific glutathione metabolites that activate transport systems encoded by the kefB and kefC gene products. Formation of N-ethyl-succinimido-S-glutathione (ESG) leads to the activation of potassium efflux via these transport systems. The addition of dithiothreitol and other reducing agents to cells reverses this process by causing the breakdown of ESG and thus removing the activator of the systems. Chlorodinitrobenzene, p-chloromercuribenzoate and phenylmaleimide provoke similar effects to NEM. Iodoacetate, which leads to the formation of S-carboxymethyl-glutathione, does not activate the systems but does prevent the action of NEM. It is concluded that the KefB and KefC systems are gated by glutathione metabolites and that the degree to which they are activated is dependent upon the nature of the substituent on the sulphydryl group.
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  • 26
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: EI Tor strains of Vibrio cholerae are capable of producing a haemolysin which they actively secrete into the growth medium. This requires translation to produce the protein at the surface of the cytoplasmic membrane and translocation across this membrane, the periplasmic space and the outer membrane. The mechanism by which this occurs is poorly understood.In addition to the structural gene for the haemolysin (hlyA), we have cloned a second adjacent gene, hlyB. By site-directed mutagenesis, specific hlyB mutants have been constructed. These mutants are defective in the secretion of HlyA in the early to mid-exponential phase of growth and the haemolysin becomes trapped within the cell and is only released in stationary phase. Nucleotide sequence analysis and cell fractionations reveal HlyB to be a 60.3 kD putative outer membrane-associated protein.
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  • 27
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The fhuE gene of Escherichia coli codes for an outer-membrane receptor protein required for the uptake of iron(III) via coprogen, ferrioxamine B and rhodotorulic acid. The amino acid sequence, deduced from the nucleotide sequence, consisted of 729 residues. The mature form, composed of 693 residues, has a calculated molecular weight of 77453, which agrees with the molecular weight of 76000 determined by poly-acrylamide gel electrophoresis. The FhuE protein contains four regions of homology with other TonB-dependent receptors. A valine to proline exchange in the ‘TonB box’ absolished transport activity. Phenotypic revertants with substitutions of arginine, glutamine, or leucine at the valine position exhibited Increasing iron-coprogen transport rates. Point mutations resulting in the replacement of glycine (127) in the second homology region with either alanine, aspartate, valine, asparagine or histidine exhibited decreased transport rates (listed in descending order). A truncated FhuE protein lacking 24 amino acids at the C-terminal end was exported to the periplasm but failed to be inserted into the outer membrane.
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  • 28
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: P.11 outer membrane proteins of Neisseria gonorrhoeae are encoded by a family of closely related genes. Although the genes are highly conserved, major differences in sequence among them occur in two short regions, designated hypervariable regions 1 (HV1) and 2 (HV2). In this study, we determined the number and DNA sequence of the hypervariable regions in the P.11 genes of strain FA1090. The FA1090 chromosome contained at least eleven P.11 loci, having six different versions each of HV1 and HV2 among them. Southern blotting with HV-specific oligonucleotides showed that each version was present in one to three copies, and that there were nine unique combinations of HV1 and HV2 in the P.M genes. Although each of the versions of HV1 or HV2 had a unique DNA sequence, there were some similarities among them, particularly when certain ones were compared. Restriction fragments containing only the HV regions were cloned into an expression vector to demonstrate that the epitopes recognized by a set of monoclonal antibodies specific for different FA1090 P.11 proteins were completely encoded by either HV1 or HV2.
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  • 29
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The genes encoding the acetate-inducible enzyme acetyl-coenzyme A synthetase from Neurospora crassa and Aspergillus nidulans (acu-5 and facA, respectively) have been cloned and their sequences compared. The predicted amino acid sequence of the Aspergillus enzyme has 670 amino acid residues and that of the Neurospora enzyme either 626 or 606 residues, depending upon which of the two possible initiation codons is used. The amino acid sequences following the second alternative AUG show 86% homology between the two species; the extended N-terminal sequences show no homology. The Neurospora protein is characterized by the appearance of the S(T)PXX sequence motif where the amino acid homologies break down. The codon usage is biased in both genes, with a marked deficiency, especially in Neurospora, of codons with A in the third position.The facA transcribed sequence contains six introns: one in the long leader sequence, one in the 5′ coding sequence not homologous with acu-5, and four within the sequence that is largely similar to that of acu-5. Only one intron, corresponding in size and position to the furthest downstream of the facA introns, is found in acu-5. The evolution of introns during the divergence of these two Ascomycete fungi is discussed. Each of the two genes has been transferred by transformation into the other species. Each species is evidently able to splice out the other's introns. Most transformants have normal acetate-induction of acetyl-CoA synthetase, emptying that the two genes respond to transcriptional control signals common to both species, in spite of the striking divergence of their 5′ ends.
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  • 30
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Two major 60kD protein species can be separated by differential detergent extraction in Chlamydia spp. A Sarkosyl-soluble 60kD protein is (i) structurally and antigenically distinct from the previously characterized 60kD Omp2 outer membrane protein; and (ii) antigenically related to a bacterial common antigen of similar molecular weight which includes a 65 kD myco-bacterial antigen and the GroEL heat-shook protein of Escherichia coli. Among GroEL homologues, the chlamydial protein (chl-GroEL) uniquely displays affinity towards immobilized thiol groups. The significance of this property is discussed with respect to the synthesis and assembly of the chlamydial disulphide-rich cell wall late in the growth cycle. Chl-GroEL is identical to the Triton X-100-soluble, ocular delayed-type hypersensitivity agent (Morrison et al., 1989), an essential component in the development of blinding trachoma. An autoimmune mechanism for chronic chlamydial diseases based on chl-GroEL homology to host proteins is hypothesized.
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  • 31
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: As an initial approach in the study of the mechanism of secretion of the extracellular heat-stable enterotoxin of Escherichia coli (STA), and in order to use this polypeptide as an extracellular carrier we previously constructed a fusion between the complete STA toxin (pre-pro-STA) and the mature B subunit of the periplasmic heat-labile enterotoxin (LTB); the resulting STA-LTB hybrid was not secreted to the extracellular environment, and cells expressing the hybrid lysed at temperatures above 35°C. In this work we have established that the hybrid is initially detected as pre-pro-STA-LTB and converted to pro-STA-LTB, which lacks the 19amino acids that share the properties of a signal peptide; the sequenced 17 amino-terminal residues of pro-STA-LTB defined the processing site of pre-pro-STA-LTB at pro_3phe_2ala_1 ↓ gln+1. This process was sensitive to an energy uncoupler (CCCP) and was correlated with translocation of pro-STA-LTB across the inner membrane. Additionally, we are able to show that although pre-pro-STA-LTB is processed at 37°C and 29°C, it is more efficiently processed at the latter temperature. At 37°C, pro-STA-LTB was poorly released into the periplasm, resulting in accumulation of this protein, pre-pro-STA-LTB, and pre-β-lactamase in the inner membrane, and in cell lysis. In contrast, at 29°C pro-STA-LTB was localized in the periplasm and in the inner membrane, and pre-pro-STA-LTB and pre-β-lactamase did not accumulate; however, translocation of periplasmic pro-STA-LTB across the outer membrane still did not occur, and a second processing step that would eliminate the pro segment from pro-STA-LTB was never observed. Thus, the fusion of pre-pro-STA and LTB resulted in a polypeptide that, while incompatible with secretion to the extracellular medium, is exported to the periplasm in a temperature-conditional fashion. This latter observation is consistent with an STA secretion pathway whereby pre-pro-STA is first processed to periplasmic pro-STA by the removal of 19-amino-acid signal peptide.
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  • 32
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Expression of the gene of the methanol-soluble, heat-stable enterotoxin of Escherichia coli (STA) allowed the identification by SDS-PAGE of a cell-associated 7500 Dalton STA-related peptide; when similar experiments were performed with a phosphate buffer SDS-PAGE system, an additional Mr9800 band became apparent. The 9800 Dalton form, pre-pro-STA, accumulated as an intracellular species when the experiments were performed in the presence of the proton ionophore CCCP (carbonylcyanide m-chlorophenylhydrazone); by pulse-chase experiments, it was shown that pre-pro-STA became a periplasmic Mr 7500 pro-STA and this form was chased to the culture supernatant; periplasmic and extracellular pro-STA showed the same electrophoretic mobility. A short time after the pulse, pro-STA was converted extracellularly to mature STA (Mr 4500). It is proposed that STA is synthesized as pre-pro-STA, a 72-amino-acid peptide that is subsequently cleaved between amino acids 19 and 20as it is translocated across the inner membrane. The resulting 53-amino-acid pro-STA is first detected in the periplasm and is then secreted to the culture supernatant. Pro-STA is cleaved extracellularly to yield mature STA (Mr 4500).
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  • 33
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have isolated a Salmonella typhimurium (ST) mutant, JKS400, deficient in the production of a surface-exposed outer membrane protein (Omp) and phenotypically hypersensitive to the oxidative antimicrobial mechanism of polymorphonuclear leukocytes (PMNs). This Omp migrated at approximately 59 kiloDaltons (kD) in sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). We found with P22 transduction that the capacities to produce the protein and to exert wild-type resistance to oxidative killing were tightly linked.Transduction of JKS400 with a P22(HT)Ht bacteriophage grown on a Tn10 insertion library in LT2 yielded tetracycline-resistant isolates that had been returned to wild-type protein production. Further experiments showed that restoration of protein production was accompanied by restoration of the parental resistance phenotype to killing by PMNs and by restoration to wild-type resistance to H2O2. The map position of the Tn10 was determined to be at 96 minutes in the Salmonella chromosome.This protein appears to behave as a virulence factor, promoting the capacity of Salmonella typhimurium LT2 to survive oxygen-dependent killing mechanisms in neutrophils.
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  • 34
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The gerA operon of Bacillus subtilis 168 comprises three genes concerned with the triggering of spore germination by l-alanine and its analogues. The expression of this operon has been characterized using chromosomal lacZ fusions to the gerA promoter. The gerA promoter is switched on 2.5–3 hours after the initiation of sporulation, in parallel with glucose dehydrogenase. A high proportion of the gerA-driven β-galactosidase detected in sporulating cells is found in the mature spore; the gerA promoter is therefore active in the forespore compartment of the sporulating cell. The gerA promoter is not expressed in spo0, spoII or spoIIIA, B, E and G mutant backgrounds, but is expressed in spoIIICand D and in spoIV and V mutants. The in vivo transcriptional startpoint of the operon has been mapped by primer extension experiments; sequences upstream from this startpoint show significant homology with recognition sequences for RNA polymerase containing σG(EσG). The gerA operon was transcribed in vitro by EσG with a startpoint identical to that used in vivo, and expression of the gerA operon was rapidly induced in vegetative cells by induction of σG synthesis. These data indicate that the gerA operon is an additional member of the σG regulon, which includes a number of genes expressed in parallel only in the forespore compartment of sporulating B. subtilis cells.
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  • 35
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: TonB protein serves as an energy transducer to couple cytoplasmic membrane energy to high-affinity active transport of iron siderophores and vitamin B12 across the outer membranes of Gram-negative bacteria. The biochemical mechanism of the energy transduction remains to be determined, but important details are already known. TonB is targeted to and anchored in the cytoplasmic membrane by a single membrane-spanning domain and spans the periplasm to physically interact with outer-membrane receptors of the transport ligands. TonB-dependent energy transduction is modulated by ExbB protein, which stabilizes TonB, and possibly by several other proteins including ExbC, ExbD, and TolQ. TonB has a relatively short functional half-life that is accelerated when rates of active transport across the outer membrane are increased. A model that incorporates this information, as well as some tempered speculation, is presented.
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  • 36
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Cells of Escherichia coli possess high-affinity active transport systems of vitamin B12 and iron-siderophore complexes. Specific outer-membrane proteins carry out the energy-dependent transport across the outer membrane, in conjunction with the TonB coupling protein. Mutagenesis experiments have identified a conserved region near the amino-terminus of the outer-membrane transporters that is necessary for energy-coupled transport. The ability of extragenic suppressor mutations in tonB to correct the transport defect indicates that TonB couples the proton-motive force to the outer-membrane proteins by direct contact.
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  • 37
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    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Uncharged tRNA has been shown in vivo to have an active role both in the stringent response, and in modulating the rate of translational elongation. Both of these effects appear to be mediated by codon–anticodon interactions on the ribosome. Although the involvement of uncharged tRNA in the stringent response was expected from in vitro experiments, it has only recently been confirmed in vivo. Inhibition of translation by cognate uncharged tRNA was not expected, and a model is proposed in which excess uncharged tRNA competes with charged tRNA (in ternary complex) for the 30S component of the ribosomal A site. When uncharged tRNA is in sufficient excess over charged tRNA, interaction of uncharged tRNA with the 50S component of the A site occurs as well, leading to a stringent response. The cell has a continuum of responses to decreasing aminoacyl-tRNA levels: in moderately limited conditions, the proportion of uncharged tRNA increases, and the translation rate is slowed; under more severe limitations, uncharged tRNA provokes a stringent response, with pleiotropic consequences for the cell.
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  • 38
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The DNA sequence of the K99 fanF gene, encoding FanF, was determined. An open reading frame of 999bp was found. The primary structure of FanF was deduced and analysis revealed the presence of a signal sequence of 22 amino acid residues. The mature protein contains 311 amino acid residues (Mr 33905 D). The amino acid sequence of FanF showed similarity with the K88ab major subunit FaeG.A specific mouse antiserum against FanF was prepared by constructing and purifying a hybrid CroLacZ-FanF protein. Minicell analysis, immunoblotting and immunoelectronmicroscopy revealed a pool of FanF in the periplasm of K99-producing cells and showed, furthermore, that FanF Is a minor component of K99 fibrillae, present at the top and in or along the shaft of the K99 fibrillar structures.A fanF mutant plasmid was constructed. Cells harbouring this plasmid produced all K99-specific proteins, except FanF, but produced 0.1% of the K99 fibrillae relative to ‘normal’ K99-producing cells. Electron microscopic observations showed that cells defective in fanF produce only a few (apparently short) K99 fibrillae. FanF, therefore, was supposed to play a role in initiation and elongation of K99 fibrillae formation.Thin-layer chromatography experiments involving purified receptor material showed that FanF is not required for binding of K99 fibrillae to the ganglioside receptor. Fibrillae produced by an adhesion-negative strain carrying a mutation in the K99 major fibrillar subunit were shown to contain a normal amount of FanF.
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  • 39
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Resistance to intercalating dyes (ethidium, acriflavine) and other organic cations, such as quaternary ammonium-type antiseptic compounds, mediated by the Staphylococcus aureus ptasmid pSK1 is specified by an energy-dependent export mechanism encoded by the qacA gene. From nucleotide sequence analysis, qacA is predicted to encode a protein of Mr 55017 containing 514 amino acids. The gene is likely to initiate with a CUG codon, and a 36bp palindrome immediately preceding qacA, along with an upstream reading frame with homology to the TetR repressors, may be components of a regulatory circuit. The putative polypeptide specified by qacA has properties typical of a cytoplasmic membrane protein, and is indicated to be a member of a transport protein family that includes proteins reponsible for export-mediated resistance to tetracycline and methylenomycin, and uptake of sugars and quinate. The analysis suggests that N- and C-terminal regions of these proteins are involved in energy coupling (proton translocation) and substrate transport, respectively. The last common ancestor of the qacA and related tet (tetracycline resistance) lineages is inferred to have been repressor controlled, as occurs for modern tet determinants from Gram-negative, but not those from Gram-positive, bacteria.
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  • 40
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Studies of the equilibrium between native and denatured forms of wild-type levansucrase showed that the denatured form was predominant at 37°C and pH 7 in the absence of free metal. The shift to the native form was promoted by metal ions such as Fe3+ or Ca2+. This metal-dependent refolding process was not observed in levansucrase variants bearing the amino acid substitution Gly-366→Asp or Gly-366→Val. These variants were only slightly secreted by Bacillus subtilis although their signal sequences were normally cleaved and their exocellular forms stable. In contrast, the Gly-366→Ser variant was secreted at near-normal levels and shared a part of the in vitro refolding properties of the wild-type protein. These differential properties might be related to the ability of the altered region to form a β-turn structure.We discuss the possible role of metal ions in the coupling of protein folding and secretion.
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  • 41
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The DNA repeat region of fcrA76, the gene encoding a group A streptococcal Fc-binding protein, was sub-cloned in-frame into an Escherichia coli plasmid expression vector. The expressed protein product displayed the same Fc-binding properties as the full-length Fc-binding protein expressed from fcrA76. The affinity-purified, full-length Fc-binding protein was found to compete with staphylococcal protein A or streptococcal protein G for binding to beads coated with human IgG. These results are consistent with earlier studies suggesting that the binding sites on human IgG for protein A, protein G and the type II Fc-binding protein from group A streptococci are located at the interface of the CH2 and CH3 domains of the Fc region.
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  • 42
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The budding yeast Saccharomyces cerevisiae has a finite life span that is defined by the number of times the cell divides. The patterns of expression of certain genes change in a specific manner during the life span, implying that at least some of the manifestations of the ageing process are subject to gene regulation. It has now been determined that the controlled expression of the RAS oncogene in yeast increases the longevity of this organism, indicating that, conversely, a defined alteration in the activity of a single gene can extend this organism's life span. The results suggest that there is a balance between life-span extension and growth arrest when RAS is expressed. Inasmuch as the homologues of RAS in yeast function to integrate cell metabolism with the cell cycle, these studies raise the possibility that this integrative function may also apply to the co-ordination of successive cell cycles during the life span.
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  • 43
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Listeriotysjn O (LLO), a major virulence factor of the intracellular bacterium Listens monocytogenes, shares with other known ‘thiol-activated toxins’ a conserved undecapeptide, ECTGLAWEWWR, located in the C-terminal region of the protein and containing the unique cysteine of the molecule. Single amino acid substitutions were created in this region to study the role of cysteine and tryptophan residues in the lytic activity of LLO as well as in the virulence of the bacterium. Transformation of a transposon-induced non-haemolytic mutant with plasmids carrying the mutated genes allowed allele exchange and transfer of mutations on to the chromosome by in vivo recombination. The mutant strains secreted a full-length 59 kilodalton LLO. A decrease of 25% in the haemolytic activity in culture supernatants was observed in the case of mutation Cys-484 to Ala and of 80% for mutation Cys-484 to Ser. Mutations Trp-491 and Trp-492 to Ala decreased activity by, respectively, 95% and 99.9%. LLOs produced by the mutants, as the wild type, were active at low pH, inhibited by cholesterol, and able to bind to cell membranes. A close relationship was found between virulence of mutants in the mouse model and haemolytic activity in their culture supematants. These results demonstrate that the thiol group of Cys-484 is not essential for either haemolytic activity in vitro or virulence in vivo. In contrast, Trp-492 appears to be required for both haemolytic activity and virulence. The finding that the nearly non-haemolytic mutant Trp-492-Ala persisted in the spleen for several days after inoculation indicates that mutagenesis of a virulence determinant can attenuate virulence and provides a novel approach to the development of live vaccine strains.
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  • 44
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A lysogen of Streptomyces coelicolor A3(2) containing a thermoinducible mutant of the temperate phage φC31 (φ C31 cts1) was used to obtain synchronous phage development. Filter hybridization experiments indicated a marked reduction in rRNA synthesis after prophage induction. S1 nuclease mapping showed that transcription from each of the four promoters of one rRNA gene set (rrnD) was reduced to approximately the same extent, and that inhibition required protein synthesis. Crude preparations of RNA polymerase from induced lysogens had enhanced transcribing acitivity for φC31 DNA which was lost upon further purification. The purified preparations were unimpaired in their ability to transcribe from the rrnD promoters in vitro and apparently unchanged in poly-peptide composition. The factor(s) responsible for stimulating phage transcription, and possibly for inhibiting rRNA synthesis, may have been separated from the enzyme during purification.
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  • 45
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Addition of purine compounds to the growth medium of Escherichia coli and Salmonella typhimurium causes repressed synthesis of the purine biosynthetic enzymes. The repression is mediated through a regulatory protein, PurR. To identify the co-repressor(s) of PurR, two approaches were used: (i) mutations were introduced into purine salvage genes and the effects of different purines on pur gene expression were determined; (ii) purine compounds which dictate the binding of the PurR protein to its operator DNA were resolved by gel retardation. Both the in vivo and the in vitro data indicated that guanine and hypoxanthine are co-repressors. The toxic purine analogues 6-mercaptopurjne and 6-thioguanine also activated the binding of PurR to its operator DNA.
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  • 46
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The β-lactam antibiotic cloxacillin can inhibit secretion of prokaryotic lipo-β-lactamase into the periplasm of yeast. The results indicate that this phenomenon is specific with respect to both the antibiotic and the lipo-β-lactamase whose secretion is affected, strongly suggesting that this involves an interaction between the enzyme and its substrates. The effect of the antibiotic on secretion is reversible. With different β-lactam antibiotics, the clearest difference is observed between type A and type S penicillins; the former exert a strong inhibition of secretion whereas the latter exhibit a weak effect or no effect at all. Type A penicillins have been previously shown to cause a conformational change in various β-lactamases. Mature lipo-β-lactamase species in yeast were localized either to the periplasmic space or bound to the outer surface of the cytoplasmic membrane and thus exposed to periplasm. The results are consistent with the hypothesis that binding of cloxacillin to lipo-β-lactamase induces a conformation on the protein that is unfavourable for its release from the membrane.
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  • 47
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: An msDNA operon, consisting of genes for msDNA and a reverse transcriptase, is present in Escherichia coli B and absent from E. coli K12. We have found that the msDNA operon is located on a DNA fragment, longer than 15 kb, that is absent from E. coli K12. Using conjugation, P1 transduction, and nucleic acid hybridization between E. coli B and E. coli K12 strains, we have located the position of the msDNA operon on the E. coli B chromosome at a site that corresponds to minute 19 on the genetic map and to position 900 on the physical map of the E. coli K12 chromosome.
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  • 48
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Many photosynthetic bacteria from aquatic and terrestrial habitats reduce atmospheric dinitrogen to ammonia. The synthesis of proteins required for nitrogen fixation in these microorganisms is repressed by fixed nitrogen or oxygen. Studies on the purple non-sulphur phototroph Rhodobacter capsulatus have helped to clarify this transcriptional control and to define the factors involved in this regulation. The molecular mechanisms by which the nitrogen and oxygen status of the cell are relayed into nif gene expression or repression involve many trans- and cis- acting factors. The roles of these factors in the nif regulatory cascade of R. capsulatus are summarized. Two levels of control are present. The first level of control involves the nitrogen sensing circuitry in which at least four proteins act in a cascade. Upon nitrogen deficiency, genes involved in the second level of control are transcriptionalty activated. These genes encode regulatory proteins that subsequently activate transcription of all other nif genes under anaerobic conditions. The R. capsulatus cascade is compared to the nif regulatory cascade in Klebsiella pneumoniae, highlighting both common and unique aspects.
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  • 49
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The hok/sok system of plasmid R1, which mediates plasmid stabilization via killing of plasmid-free segregants, encodes two genes: hok and sok. The hok gene product is a potent cell-killing protein. The expression of hok is regulated post-transcriptionally by the sok gene-encoded repressor, an antisense RNA complementary to the hok mRNA leader region. We show here that the hok mRNA is very stable, while the sok RNA decays rapidly. We also observe a new hok mRNA species which is 70 nucleotides shorter in the 3′-end than the full-length hok transcript. The appearance of the truncated hok mRNA was found to be regulated by the sok antisense RNA. Furthermore, the presence of the truncated hok mRNA was found to be correlated with efficient expression of the Hok protein. On the basis of these findings, we propose an extended model in order to explain the killing of plasmid-free segregants by the hok/sok system.
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  • 50
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Maximum expression of the Corynebacterium glutamicum lysA gene is dependent upon the presence of a 2.3 kb region immediately 5’of the lysA reading frame. Subcloning and functional analysis of the upstream region implied that this region contained the lysA promoter. Sequence determination of the upstream region revealed a single open reading frame, orfX, in the same orientation as lysA. The orfX coding sequence exhibited all the sequence characteristics of a gene with the potential for a 550-amino-acid polypeptide product. Expression of lysA is coupled to that of orfX via a common promoter located immediately 5 of orfX. The RNA start site has been determined by S1 nuclease mapping. Both the orfX and the lysA gene are expressed as a single 3.0kb RNA transcript. These data indicate that orfX and lysA are genes within a two-gene operon. Expression of the lysA gene is not subject to regulation by lysine. The orfX gene product was shown not to be directly linked to the lysine biosynthetic pathway, nor is it the enzyme incorporating DAP into the peptidoglycan precursor.
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  • 51
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    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The par locus is a segment of pSC101 that has been identified as a cis-acting determinant of plasmid stability. We show that par also determines copy number and must, therefore, play a role in plasmid replication. The segregation defect, but not the copy-number reduction, of par- replication origins is completely suppressed by a short sequence from the bacteriophage lambda gene O which is present in plasmid pKO-4. Thus, replication and segregation functions are separable from each other.
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  • 52
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The nucleotide sequence of a 5.1 kb region in the Haemophiius influenzae type b capsulation locus has been determined and found to contain four open reading frames: bexD, bexC, bexB, and bexA. Comparison of the deduced products of bexC, bexB, and bexA to known proteins, and TnphoA mutagenesis, suggests that they form components of an ATP-driven polysaccharide export apparatus. Furthermore, close sequence similarity between BexA and BexB and products of the kpsT and kpsM genes at the Escherichia coli K5 capsulation locus (Smith et al., 1990 — accompanying paper) suggests that capsulation genes in these organisms may have a common ancestry.
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  • 53
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The effect of the unc transcription terminator on expression of uncC, encoding the e subunit of Escherichia coli F1-ATPase, from plasmids was studied. The cloned sequence in pTK1 included the uncC ribosome binding site, the uncC structural gene, and unc transcription terminator. The cloned region in pSD37 was similar, but lacked the unc transcription terminator. Transformants carrying pTK1 produced the e subunit of F1-ATPase, encoded by uncC, in 10-fold greater abundance than transformants carrying pSD37. Northern blots revealed similar differences in the steady-state uncC mRNA levels. The half-life of the message transcribed from pTK1 was 90–100 seconds, while that from pSD37 was 25–30 seconds. These studies indicate the importance of message stabilization through features at the 3 end of the transcript in ensuring adequate production of. We have exploited this stabilization to develop a simple, efficient, and gentle method of purifying the overproduced subunit.
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  • 54
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The majority of clinical isolates of Staphylococcus aureus that produce toxic shock syndrome toxin-1 (TSST-1) fail to express α-toxin, despite having a copy of the hla gene in the chromosome. The hla gene was cloned from an Hla- TSST-1+ strain, Todd 555, which had been isolated from a case of toxic shock syndrome in the USA. Of the 630 bases of the Todd 555 gene sequenced, 46 differed from the hla gene sequence of strain Wood 46. The defect in α-toxin expression was shown to be due to a nonsense mutation which converted a CAG glutamine codon in the equivalent position in the functional Wood 46 sequence to a TAG stop codon. The same mutation was present in the hla gene cloned from a human septicaemia strain (V37) isolated in Dublin. The nonsense mutation of Todd 555 was suppressed by the supE 44 mutation in Escherichia coli resulting in haemolytic activity in cell lysates. Hybrid hla genes were formed by splicing fragments of hla from Todd 555 and Wood 46. Expression of one such chimaeric hla gene in S. aureus demonstrated that the Todd 555 hla gene has a functional agr-regulated promoter. The silent hla gene may be a cryptic gene in S. aureus.
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  • 55
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Bacillus thuringiensis subspecies kurstaki (Btk) and subspecies berliner (Btb) both produce lepidopteran-specific larvicidal protoxins with different activities against the same insect species. Toxic activity resides in the amino-terminal half of both protoxins, whereas the carboxy-terminal half of the molecules is not required for toxicity. The protoxins are 90% homologous, with a major cluster of differences in the amino-terminal half, and a 26 consecutive amino-acid insertion within the carboxy-terminal half of the Btk protoxin. Protoxin chimeras composed of the amino-terminal half of one subspecies and the carboxy-terminal half of the other were generated. Wild-type and chimeric protoxins were compared in bioassays against tobacco horn worm larvae. The amino-terminal half, the toxin itself, dictates specific larvicidal activity.
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  • 56
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: To analyse the regulation of the nodulation (nod) genes of Rhizobium meliloti RCR2011 we have isolated lacZ gene fusions to a number of common, host-range and regulatory nod genes, using the mini-MU-lac bacteriophage transposon Mud II1734. Common (nodA, nodC, nod region IIa) and host-range (nodE, nodG, nodH) genes were found to be regulated similarly. They were activated (i) by the regulatory nodD1 gene in the presence of flavones such as chrysoeriol, luteolin and 7,3′,4′-trihydroxyflavone, (ii) by nodD2 in the presence of alfalfa root exudate but not with the NodD1-activating flavones, and (iii) by the regulatory genes syrM-nodD3 even in the absence of plant inducers. Thus common and host-range nod genes belong to the same regulon. In contrast to the nodD1 gene, the regulatory nodD3 gene was not expressed constitutively and exhibited a complex regulation. It required syrM for expression, was activated by nodD1 in the presence of luteolin and was positively autoregulated.
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  • 57
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Total DNA was isolated from the parasitic protozoan Giardia lamblia and separated into two distinct populations of different densities by centrifugation through CsCI gradients containing Hoechst dye 33258. The two populations obtained were characterized by restriction enzyme analysis and nucleic acid hybridization. The less-dense population contains non-repetitive DNA and may encode mainly structural genes, such as those for α- and β-tubulin. Digestion of the DNA with several restriction endonucleases showed that the denser band was composed of a 5.5 kb unit which contains the C. lamblia ribosomal RNA cistron in tandem repeated organization.
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  • 58
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    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The previously published sequences of the operator-promoter region of the mannitol operon of Escherichla coli and of the mtlD gene have been found to contain a number of errors. The major conclusions reported previously were correct, but additionally it is now clear that a C-terminal portion of mannitol-1-phosphate dehydrogenase (the mtlD gene product) exhibits significant sequence identity with an amino-terminal region of human liver fructose-6-phoshate-2-kinase; fructose-2,6-bishosphatase.
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  • 59
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The MNN2 gene of Saccharomyces cerevisiae has been cloned by complementation of the mnn2 mutant phenotype scored by a change in cell surface carbohydrate structure resulting from a lack of α1→2-man-nose branching in the outer chain. The gene was subcloned as a 3 kb DNA fragment that integrated at the MNN2 locus, and a gene disruption yielded the mnn2 phenotype. A lacZ–MNN2 gene fusion protein, produced in Escherichia coli, was used to raise a specific antiserum that recognized a 65kD wild-type yeast protein. This MMN2 gene product lacks N-linked carbohydrate but appears to be an integral membrane protein. Overproduction of MNN2p does not enhance the α1→2-mannosyltransferase activity of yeast cells. The results suggest that MNN2p is a Golgi-associated protein that is involved in mannoprotein sorting rather than glycosylation.
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  • 60
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    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Metal ions are essential cofactors in several transacting bacterial gene regulators. Upon binding of the metal, the receptor proteins act either as repressors of gene expression or, in other systems, as transcriptional activators. Other metal-dependent regulatory proteins may function, directly or indirectly, as sensors of the cellular oxygen status, and may even be mediators in light-responsive gene regulation.
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  • 61
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Production of β-lactamases, and of the plasmid-encoded TEM-and SHV-type enzymes in particular, is the most common mechanism of resistance against β-lactam antibiotics in Gram-negative bacteria. The two ubiquitous types of enzyme have a large spectrum of activity and preferentially hydrolyse the penicillins as well as some first-and second-generation cephalosporins. Recently, point mutations in the corresponding genes have been observed, apparently selected for, in the clinical setting, by originally ‘β-lactamase-stable’ third-generation cephalosporins or by mono-bactams, which fall into the substrate range of the mutant or ‘extended-spectrum’β-lactamases. The point mutations are clustered in three areas, each adjacent to one of the seven evolutionarily conserved boxes described by Joris et al. (1988). The substituted amino acids at positions 102 (adjacent to the α-3 helix), 162 (adjacent to the α-7 helix) and 235,236 and 237 (on the β-3 strand) are located in close proximity to the active-site cavity and are thought to open up novel enzyme-substrate interactions, involving, in particular, the oxyimino moieties of the newer β-lactam compounds.
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  • 62
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    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Many microorganisms metabolize their substrates (precursors) only partially and excrete the products of the metabolism into the medium. Although uptake of precursor and exit of product can proceed as two independent steps, there is increasing evidence that these processes are often linked and that transport is facilitated by a single antiport mechanism. Features of antiport mechanisms and advantages for the organism of catalysing precursor/product antiport will be illustrated by discussing a number of well-characterized systems. Based on precursor-product conversion stoichiometries, structural relatedness between precursors and products, and energetic and kinetic considerations, new examples of antiport systems will be proposed.
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  • 63
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    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The enzyme TEM β-lactamase constitutes a versatile gene-fusion marker for studies on membrane proteins and protein export in bacteria. The mature form of this normally periplasmic enzyme displays readily detectable and distinctly different phenotypes when localized to the bacterial cytoplasm versus the periplasm, and thus provides a useful alternative to alkaline phosphatase for probing the topology of cytoplasmic membrane proteins. Celts producing translocated forms of β-lactamase can be directly selected as ampicillin-resistant colonies, and consequently a β-lactamase fusion approach can be used for positive selection for export signals, and for rapid assessment of whether any protein expressed in Escherichia coli inserts into the bacterial cytoplasmic membrane. The level of ampicillin resistance conferred on a cell by an extracytoplasmic β-lactamase derivative depends on its level of expression, and therefore a β-lactamase fusion approach can be used to directly select for increased yields of any periplasmic or membrane-bound gene products expressed in E. coli.
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  • 64
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Single-stranded plasmid DNA, containing the mnt gene, was replicated in vitro with DNA polymerase III holoenzyme. Escherichia colimutH bacteria, defective in mismatch repair, were transformed with the products of in vitro synthesis. Mutations in mnt were readily identified and 33 out of 65 isolates were single base changes including transition, transversion and frameshift mutations. The remaining 32 isolates were deletions of apparently random length and substitutions (deletion/insertions). The intergenic deletions as well as the transition and frameshift mutations were identical to those previously isolated from mismatch repair-defective cells in vivo.
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  • 65
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Differentiation of microorganisms for taxonomic purposes is based primarily on phenotypic characteristics, which are the direct or cumulative result of gene expression. Since expression of phenotypic characteristics usually relies on in vitro growth of a microorganism, non-cultivable organisms, such as Mycobacterium leprae, present major problems for the identification of potential variants based on phenotypic similarities or differences between individual isolates. We have employed the use of restriction fragment-length polymorphism (RFLP) analysis of chromosomal DNA of M. leprae isolates, including human isolates from geographically distinct regions of the world and isolates from a Sooty Mangabey monkey and an armadillo, to assess the relatedness among these isolates. Restriction endonuclease (Eco RI, Bst EII, Pst I, and Pvu I) digests of chromosomal DNA were analysed using DNA probes encoding all or part of the 12kD, 18kD, 28kD, 65kD and 70kD proteins of M. leprae as well as a probe containing an M. leprae-specific sequence repeated up to 20 times in the M. leprae chromosome. Comparison of the resulting autoradiographs showed that the RFLP patterns were all identical, indicating that these isolates contained no polymorphism with respect to the restriction endonuclease sites analysed. In addition, RFLP patterns of two separate human M. leprae isolates remained unchanged after three cycles of experimental infection in the armadillo model. These results indicated that the M. leprae isolates tested in this study were indistinguishable at the genotypic level, strongly suggesting homogeneity among members of this species.
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  • 66
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The interaction with HeLa cells of an enteropathogenic Escherichia coli (EPEC) strain and its plasmid-cured derivative strain was examined. An O111:NM EPEC strain B171 harbours a 54 megadalton plasmid (pYR111) necessary for the expression of both localized adherence (LA) to HeLa cells and the 0-repeating side chain of the lipopolysaccharide. Under light microscopy, the plasmid-cured derivative strain B171-4 was observed to interact with HeLa cells in a pattern distinct from LA. Transmission electron microscopy showed that the bacteria were internalized by HeLa cells. In contrast, strain B171 induced pedestal-like projections and invaginations of the plasma membrane, but was never completely internalized. A quantitative assay to determine the number of internalized bacteria revealed that strain B171-4 was internalized at levels 30–70-fold higher than those of aviruient E. coli strains. Cytochalasin B reduced the levels of internalization of both strain B171-4 and an entero-invasive E. coli strain (E11), but did not affect LA by strain B171. These results suggest that EPEC strain B171 may carry a specific chromosomally determined surface factor needed to initiate internalization by HeLa cells. However, a plasmid-determined factor alters the nature of this interaction; the combined effects of the chromosomal and plasmid determinants lead to the characteristic attachment of the bacteria in clusters on the surface of the eukaryotic cell.
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  • 67
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: To shed more light on the controversial findings concerning the functional participation of the highly conserved nut-like leader box A sequence element in ribosomal RNA transcription antitermination we have carried out a mutational study. We have substituted the box A and combined this mutation with several deletions comprising the rRNA leader elements box B, box C and the tL region. The mutations are located within the genuine rrnB operon cloned on multicopy plasmids. We determined the effects of the mutations on cell growth, rRNA accumulation and ribosomal subunit stoichiometry. Cells transformed with the mutated plasmids were affected in their growth rate, and showed a surprising deficiency of the promoter-proximal 16S compared to the 23S RNA, indicative of a post-transcriptional degradation event. Accordingly, we could demonstrate a reduced amount of free 305 relative to 50S ribosomal subunits in exponentially growing cells. Similar stoichiometric aberrations in the ribosome pool were detected in conditionally Nus factor-defective strains. The results show that the leader box A sequence within rRNA operons has important post-transcriptional functions for 16S RNA stability and ribosomal subunit stoichiometry. A model is proposed, describing the biogenesis and quality control of ribosomes based on rRNA leader and Nus-factor interactions. It is compatible with the previously observed effects of box A in antitermination.
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  • 68
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Streptomyces coelicolor produces spores whose development of a grey colour requires the activity of the whiE locus. The cloned whiE locus was identified after mobilization into a whiE mutant of a library of S. coelicolor DNA inserted into a transmissible plasmid vector. The whiE region of the cloned DNA was localized both by subcloning and by mutagenesis of the cloned DNA with the Streptomyces transposon Tn4560. Nucleotide sequencing of this region revealed seven open reading frames, of which six show homo-logy at the level of deduced gene products with genes involved in the synthesis of polyketide antibiotics. A previously described S. coelicolor DNA segment encoding biosynthesis of a brown pigment (Horinouchi and Beppu, 1985) corresponds to the cloned whiE DNA. It is proposed that whiE is normally expressed only in the aerial hyphae, where the biosynthetic product is responsible for spore colour.
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  • 69
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: From the effects of 13 deletions and three linker-scanner mutations at the Escherichia coli nirB promoter we have located sequences necessary for FNR-dependent induction of activity by anaerobiosis and further nitrite-dependent stimulation of expression. We describe a nirB promoter derivative that allows the cloning of ‘cassettes’ carrying different FNR-binding sequences and experiments in which a number of point mutations were introduced into these sequences. FNR-dependent stimulation of expression from the nirB promoter is critically dependent on the location of the FNR-binding site, and deletion or insertion of one base pair is sufficient to disrupt promoter function. We have transferred a number of cassette FNR-binding sequences from the nirB promoter to the unrelated melR promoter. The insertion of FNR-binding sequences at the melR promoter is sufficient to confer fnr-dependency on expression. However expression from these hybrid promoters is not as efficiently repressed during aerobic growth, suggesting that the function of bound FNR is dependent on the sequence context of the FNR-binding sequence.
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  • 70
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Earlier studies have suggested that glutamate may play an important role in the transition between the mitotic (vegetative) and meiotic (sporulative) stages of the life cycle in the yeast Saccharomyces cerevisiae. Glutamate is also a major excitatory neurotransmitter in the vertebrate brain, and its actions are mediated by the excitatory amino acid (EAA) family of receptors, the three best-characterized of which are the N-methyl-d-aspartate (NMDA), quisqualate (Q), and kainate (K) receptors. As an initial test of the possibility that glutamate action in S. cerevisiae might be mediated by an EAA-like receptor mechanism, the effects of ligands that define the functional domains of the vertebrate NMDA receptor have been examined. The responses of S. cerevisiae cells to ligands that act at four distinct sites on the NMDA receptor provide the first evidence for an NMDA-like receptor-mediated system involved in the control of yeast sporulation.
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  • 71
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Members of the IS3 family of insertion sequences are found in a wide range of bacteria. At least 10 members of this family carry two major open reading frames: a small upstream frame (0 phase), and a longer downstream frame In the –1 phase. The downstream frame shows significant similarity at the amino acid level. A highly conserved region of this frame also exhibits notable similarity with a region of the Integrase (endonuclease) domain of retroviruses. Although the overall transposition mechanism of the insertion sequence and retroviral elements is certainly different, the two groups may share additional common features, including a −1 frameshift resulting in the production of a fusion protein.
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