Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • 1990-1994  (101,820)
  • 1970-1974  (1)
  • 1992  (101,820)
Collection
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 294 (1992), S. 466-478 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    facet.materialart.
    Unknown
    New York, NY : Elsevier
    Keywords: Biochemistry ; Enzymes
    Notes: This is a series title, single volumes see link below.
    ISSN: 1557-7988
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    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
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    Keywords: Leukemia / therapy ; Prognosis
    Notes: Last volumes with varying subtitle and editor.
    ISSN: 0949-7021
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    Keywords: Hazardous Substances / toxicity
    Notes: Ceased with vol. 15(1999).
    Signatur Availability
    BibTip Others were also interested in ...
  • 6
    facet.materialart.
    Unknown
    Königswinter : Petersberg Verlag
    Keywords: Arbeitsgemeinschaft der Großforschungseinrichtungen (Germany) ; Research institutes / Germany ; Research ; Germany
    Notes: Ceased with ed. 1995.
    ISSN: 0935-2236
    Signatur Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: There have been many proposals for adding sound implementations of numeric processing to Prolog. This paper describes an approach to numeric constraint processing which has been implemented in Echidna, a new constraint logic programming (CLP) language. Echidna uses consistency algorithms which can actively process a wider variety of numeric constraints than most other CLP systems, including constraints containing some common nonlinear functions. A unique feature of Echidna is that it implements domains for real-valued variables with hierarchical data structures and exploits this structure using a hierarchical arc consistency algorithm specialized for numeric constraints. This gives Echidna two advantages over other systems. First, the union of disjoint intervals can be represented directly. Other approaches require trying each disjoint interval in turn during backtrack search. Second, the hierarchical structure facilitates varying the precision of constraint processing. Consequently, it is possible to implement more effective constraint processing control algorithms which avoid unnecessary detailed domain analysis. These advantages distinguish Echidna from other CLP systems for numeric constraint processing.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: We describe a representation and set of inference techniques for the dynamic construction of probabilistic and decision-theoretic models expressed as networks. In contrast to probabilistic reasoning schemes that rely on fixed models, we develop a representation that implicitly encodes a large number of possible model structures. Based on a particular query and state of information, the system constructs a customized belief net for that particular situation. We develop an interpretation of the network construction process in terms of the implicit networks encoded in the database. A companion method for constructing belief networks with decisions and values (decision networks) is also developed that uses sensitivity analysis to focus the model building process. Finally, we discuss some issues of control of model construction and describe examples of constructing networks.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: There are two pertinent themes in the study of idioms in the area of natural language processing. Firstly, idioms should be defined and located in the space of non-literal expressions. This will be the first aim of this paper. Secondly, a processing model should be developed. In this paper, the application of knowledge representation techniques in three different models for the representation and processing of idioms are discussed. The first, a symbolic procedural model extends the two-level model which was originally developed in computational morphology. The second is a simple localist connectionist model. The third, a symbolic hierarchical model, represents idioms as part of a lexicon conceived as an inheritance hierarchy. A comparison between the models is made in which the focus lies on the resolution of the ambiguity of idioms, the relation between the literal and non-literal interpretation and the syntactic flexibility of idiomatic expressions.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 11
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 12
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 13
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 14
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: The starting point for this commentary is Sacks’ and Doyle's conclusion that a central problem for qualitative physics is automating mathematical model formulation. We believe that model formulation is also a central problem for operations research, and although we have focused on models for production planning rather than for engineering systems analysis, our experience confirms that of Sacks and Doyle, that at least parts of model formulation are amenable to automation. In terms of their recommendations for future research, their strategy seems to emphasize the formalization of mathematical knowledge. We wish to stress that understanding the design or analysis context, the problem domain, and resource constraints on the modeling process is equally important. Methods used in cognitive psychology for understanding human problem solving, such as protocol analysis, can complement mathematical study by helping us understanding the processing that human modelers use to bring mathematical knowledge to bear. We have been using the results of such analyses to guide the creation of a model formulation system (MFS) within the Soar architecture. The use of cognitive studies and computer models in tandem seems to represent a viable strategy for making progress in this area.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 15
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 16
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 17
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: Sacks & Doyle provide an excellent overview of the fundamental limitations of the SPQR representations for reasoning about the qualitative properties of dynamic systems. We take this opportunity to outline some new directions for qualitative reasoning. In this paper, we provide a rigorous mathematical characterization for the term “qualitative property” in the context of static and dynamic systems. Based on these characterizations, we show that interval representations are well suited for reasoning about the qualitative properties of static systems such as qualitative comparative statics and qualitative stability. Moreover, we also show that symbolic computations help in the derivation of useful global properties of dynamic systems which can be used to guide numerical sampling of differential equations. The integration of symbolic and numeric methods provides a powerful approach for automating the qualitative analysis of differential equations.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 18
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 19
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: A truth maintenance system is a subsystem that manages the utilization of assumptions in the reasoning process of a problem solver. Doyle's original motivation for creating a truth maintenance system was to augment a reasoning system with a control strategy for activities concerning its nonmonotonic state of beliefs. Hitherto, much effort has been invested in designing and implementing the concept of truth maintenance, and little effort has been dedicated to the formalization that is essential to understanding it. This paper provides a complete formalization of the principle of truth maintenance. Motivated by Reiter and de Kleer's preliminary report on the same subject, this paper extends their study and gives a formal account of the concept of truth maintenance under the general title of assumption-based reasoning. The concept of assumption-based theory is defined, and the notions of explanation and direct consequence are presented as forms of plausible conclusions with respect to this theory. Additionally, the concepts of extension and irrefutable sentences are discussed together with other variations of explanation and direct consequence. A set of algorithms for computing these conclusions for a given theory are presented using the notion of prime implicates. Finally, an extended example on Boolean circuit diagnosis is shown to exemplify these ideas.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 20
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: Looking to the future, generators will have more knowledge of language and will have to deal with inputs that are very rich in information. As a result, several problems will become more acute, including selecting what to say at the subproposition level and dealing with interaction among goals and dependencies among choices. This paper explains how these problems arise and why they are hard to handle within traditional architectures for generation. It also discusses why these issues have not been well addressed, including the current lack of demanding applications, excessive emphasis on linguistic traditions, the use of reverse engineering to determine generator inputs, and the tendency to research only one issue at a time.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 21
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 22
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: Much research in machine learning has been focused on the problem of symbol-level learning (SLL), or learning to improve the performance of a program given examples of its behavior on typical inputs. A common approach to symbol-level learning is to use some sort of mechanism for saving and later reusing the solution paths used to solve previous search problems. Examples of such mechanisms are macro-operator learning, explanation-based learning, and chunking. However, experimental evidence that these mechanisms actually improve performance is inconclusive. This paper presents a formal framework for analysis of symbol-level learning programs, and then uses this framework to investigate a series of solution-path caching mechanisms which provably improve performance. The analysis of these mechanisms is illuminating in many respects; in particular, in order to obtain positive results, it is necessary to use a novel representation for a set of solution paths, and also to apply certain unusual optimizations to a set of solution paths. Several of the predictions made by the model have been confirmed by recently published experiments.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 23
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: Consider the construction of an expert system by encoding the knowledge of different experts. Suppose the knowledge provided by each expert is encoded into a knowledge base. Then the process of combining the knowledge of these different experts is an important and nontrivial problem. We study this problem here when the expert systems are considered to be first-order theories. We present techniques for resolving inconsistencies in such knowledge bases. We also provide algorithms for implementing these techniques.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 24
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 8 (1992), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: In this paper, I present an architecture for generating extended text. This architecture is implemented in a system, Salix, which incrementally generates natural language texts whose structure is derived from the domain structure of the subject matter. The architecture is composed of data-driven, domain-independent strategies for producing increments of text. The strategies include metastrategies that combine or choose among all strategies that are applicable at each increment or decide what to do if no strategy applies. Salix's capabilities are demonstrated in generating texts, in the domains of houses and families, that are comparable to descriptions elicited from human speakers. Salix has also been utilized to generate texts about text style (Germain 1991). The approach to text generation presented here is compared to others in the literature along the dimensions of local organization, coherence, focusing, and domain independence. An argument is made for the approach presented here that locally organizes and incrementally generates coherent text.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 25
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 14 (1992), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Notes: This article reports on a practical activity which provides a realistic context for collecting and analysing data.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 26
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 14 (1992), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 27
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 14 (1992), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Notes: This article describes two simple ways to illustrate the important concept in statistical process control known as “hunting”. The two simulations use dice and Minitab respectively.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 28
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 14 (1992), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 29
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 14 (1992), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Notes: How many sixth-formers have part-time paid employment, and does this affect their performance at A-level? This article describes how one teaching institution set up a project to collect and analyse data in an attempt to find answers to these questions.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 30
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 14 (1992), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Notes: This article classifies and discusses some of the common technical and conceptual mistakes found in the entries to student statistical project competitions in Hong Kong.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 31
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 14 (1992), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 32
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 14 (1992), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 33
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 14 (1992), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 34
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 14 (1992), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 35
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 14 (1992), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 36
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 289 (1992), S. 199-210 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 37
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Physics, Section B 386 (1992), S. 471-492 
    ISSN: 0550-3213
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 38
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Physics, Section B 373 (1992), S. 3-34 
    ISSN: 0550-3213
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 39
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 274 (1992), S. 230-238 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 40
    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.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 41
    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.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 42
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Shigella flexneri causes bacillary dysentery by invading epithelial cells of the colonic mucosa. We have characterized the icsB gene which is located on the virulence plasmid pWR100. After inactivation of icsB, the mutant strain remained invasive, but formed abnormally small plaques on HeLa cell monolayers, colonized only the peripheral cells of Caco-2 islets, and was unable to provoke a keratoconjunctivitis in guinea-pigs. Examination of infected HeLa cells showed that the icsB mutant was able to lyse the phagocytic vacuole and to form protrusions at the surface of infected cells, but, unlike the wild type, remained trapped in protrusions surrounded by two membranes. These results indicate that IcsB is involved in the lysis of the protrusions, a step necessary for intercellular spread.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 43
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Bacillus cereus cnp gene coding for the thermolysin-like neutral protease (TNP) has been cloned, sequenced, and expressed in Bacillus subtilis. The protease is first produced as a pre-pro-protein (Mr= 61000); the pro-peptide is approximately two-thirds of the size of the mature protein. The pro-sequence has been compared with those of six other TNPs, and significant homologies have been found. Additionally, the TNP pro-sequences are shown to be homologous to the pro-sequence of Pseudomonas aeruginosa elastase. A mutant has been constructed from cnp, in which 23 amino acids upstream from the pro-protein processing site have been deleted. This region has no homologous analogue in any of the other TNP pro-sequences. The detection results in a delay of six to eight hours in detection of active protease in the growth medium, as well as a 75% decrease in maximum protease production. N-terminal analysis of the mutant mature protein demonstrates that the processing site is unaltered by the pro-sequence deletion. The deletion must, therefore, modulate the kinetics of processing and/or secretion of the pro-protein.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 44
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Coumarins are inhibitors of the ATP hydrolsis and DNA supercoiling reactions catalysed by DNA gyrase. Their target is the B subunit of gyrase (GyrB), encoded by the gyrB gene. The exact mode and site of action of the drugs is unknown. We have identified four mutations conferring coumarin resistance to Escherichia coli: Arg-136 to Cys, His or Ser and Gly-164 to Val. In vitro, the ATPase and supercoiling activities of the mutant GyrB proteins are reduced relative to the wild-type enzyme and show resistance to the coumarin antibiotics. Significant differences in the susceptibility of mutant GyrB proteins to inhibition by either chlorobiocin and novobiocin or coumermycin have been found, suggesting wider contacts between coumermycin and GyrB. We discuss the significance of Arg-136 and Gly-164 in relation to the notion that coumarin drugs act as competitive inhibitors of the ATPase reaction.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 45
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The uropathogenic Gram-negative bacterium Proteus mirabilis exhibits a form of multicellular behaviour termed swarming, which involves cyclical differentiation of typical vegetative cells into filamentous, multi-nucleate, hyperflagellate swarm cells capable of rapid and co-ordinated population migration across surfaces. We observed that differentiation into swarm cells was accompanied by substantial increases in the activities of intracellular urease and extracellular haemolysjn and metalloprotease, which are believed to be central to the pathogenicity of P. mirabills. In addition, the ability of P. mirabilis to invade human urothelial cells in vitro was primarily a characteristic of differentiated swarm cells, not vegetative cells. These virulence factor activities fell back as the cells underwent cyclical reversion to the vegetative form (consolidation), in parallel with the diagnostic modulation of flagellin levels on the cell surface. Control cellular alkaline phosphatase activities did not increase during differentiation or consolidation. Non-flagellated, non-motile transposon insertion mutants were unable to invade urothelial cells and they generated only low-level activities of haemolysin, urease and protease (0–10% of wild type). Motile mutants unable to differentiate into swarm cells were comparably reduced in their haemolytic, ureolytic and invasive phenotypes and generated threefold less protease activity. Mutants that were able to form swarm cells but exhibited various aberrant patterns of swarming migration produced wild-type activities of haemotysin, urease and protease, but their ability to enter urothelial cells was three- to 10-fold lower. Analysis of haemolysin (hpmA) transcripts showed that during swarm cell differentiation there was a c. 50-fold increase in the level of the predicted major 5.2 kb and minor 6.9 kb mRNAs transcribed from the hpm operon, and assay of mRNA complimentary to urease (ureC) and flagellin (fliC) gene sequences confirmed that modulation of virulence factor activity during the swarming cycle resulted from differential expression of virulence genes in parallel with fliC gene expression. Hybridization of stage-specific mRNA with 30 random, non-overlapping chromosomal gene probes provided no evidence for universal changes in the expression of the P. mirabiis genome, suggesting that differential virulence gene expression may be a specific strategy.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 46
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Members of the GTPase superfamily are extremely important in regulating membrane signalling pathways in all cells. This review focuses on membrane-associated GTPases that have been described in prokaryotes. In bacteria, LepA and NodO are very similar to protein synthesis elongation factors but apparently have membrane-related functions. The amino acid sequences of FtsY and Ffh are clearly related to eukaryotic factors involved in protein secretion. Obg and Era are not closely related to any GTPase subgroup according to amino acid sequence comparisons, but they are essential for viability. In spite of similarities to well-studied eukaryotic proteins the signalling pathways of these cellular regulators, with the exception of NodQ, have not yet been elucidated.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 47
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A randomly generated mutation in Escherichia coli alanine tRNA synthetase compensates for a mutation in its cognate tRNA. The enzyme's mutation occurs next to a Cys-X2-Cys-X6-His-X2-His metal-binding motif that is distinct from the zinc finger motif found in some DNA-binding proteins. Instead, the synthe-tase's metal binding domain resembles the Cys-X2-Cys-X4-His-X4-Cys metal-binding domain of the gag gene product of retroviruses. For Ala-tRNA synthetase, the metal bound at the Cys His motif is important specifically for the tRNA-dependent step of catalysis, and the enzyme-tRNA interaction is dependent on the geometry of metal co-ordiNatlon to the enzyme. These data, and the demonstrated sensitivity of RNA packaging to mutations in the metal-binding domain of the gag gene product of retroviruses, suggest that an aminoacyl-tRNA synthetase and retroviruses have adopted a related metal-binding motif for RNA recognition.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 48
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The SOS response of Escherichia coli has become a paradigm for the study of inducible DNA repair and recombination processes in many different organisms. While these studies have demonstrated that the components of the SOS response appear to be highly conserved among bacterial species, as with most models, there are some significant variations. Perhaps the best example of this comes from an analysis of the SOS-like system of the developmental organism. Bacillus subtilis. Accordingly, the most striking difference is the complex developmental regulation of the SOS system as this organism differentiates into its competent state. In this review we have given an overview of the elements that comprise the SOS system of B. subtilis. Additionally, we have summarized our most recent findings regarding the regulation of this regulon. Using these results along with new findings from other laboratories we have provided provocative molecular models for the regulation of the B. subtilis SOS system in response to DNA damage and during competent cell formation.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 49
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The effect of variations in Neisseria meningitidis pili on bacterial interactions with three epithelial cell lines as well as human umbilical vein endothelial cells was studied using a panel of seven strains expressing Class I or Class II pili. Comparison of adherence of piliated and pilus-deficient variants of each strain to epithelial cells suggested that Class I pili may mediate bacterial adherence with all three epithelial cell lines. In contrast, Class II pili of the strains used did not increase bacterial adherence to Hep-2 larynx carcinoma cells, although an increase in adherence to Chang conjunctival and A549 lung carcinoma epithelial cells was observed in the Class II pili-expressing strains. In addition to these inter-class functional variations, differences in adherence to epithelial cells were also observed among Class I and Class II strains. Functionally different pilin variants of one Class I strain, MC58, were obtained by single colony isolation. One piliated variant was identified which had concurrently lost the ability to adhere to both Chang and Hep-2 cells (‘non-adherent’ phenotype; adherence of 〈 2 bacteria per cell). In addition, several adherent pilin variants were isolated from non-adherent Pil- and Pil- bacteria by selection on Chang cells (adherence of 10–25 bacteria per cell). In contrast to epithelial cells, al) variant pili, whether of Class I or Class II, adhered to endothelial cells in substantially larger numbers (〈50 bacteria per cell) and therefore implied the existence of distinct mechanisms in pilus-facilitated interactions of N. meningitidis with endothelial and epithelial cells.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 50
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A segment of the exotoxin A gene of Pseudomonas aeruginosa, coding for the N-terminal end of domain I and domain II of the toxin (ETA), was genetically fused to the diphtheria toxin gene of Corynebacterium diphtheriae, coding for the N-terminal end of A fragment of diphtheria toxin (DT). The resulting hybrid protein (termed CED1) was produced in large amounts and exported to the periplasm in Escherichia coli. This chimaeric protein reacted with both anti-ETA and anti-DT antisera. Furthermore, the chimaeric protein displayed ADP-ribosylation activity and exhibited cytotoxicity to mouse 3T6 fibroblasts. These results demonstrated that the chimaeric protein is cytotoxic, and that the toxic potential of DTA can be selectively internalized and translocated via domains I and II of exotoxin A, which are thus sufficient to direct and translocate an enzymatically active heterologous polypeptide segment into the cytosol of sensitive cells.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 51
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have developed a system of transposon mutagenesis for bacteriophage T4. The transposon is a plasmid derivative of Tn5 which contains the essential T4 gene 24, permitting a direct selection for transposition events into a gene 24-deteted phage. The transposition occurred at a frequency of only 10-7 per progeny phage, even though a dam- host was used to increase transposition frequency. Phage strains with a transposon insert were distinguished from most pseudorevertants of the gene 24 deletion by plaque hybridization using a transposon-specific probe. Mapping analysis showed that the transposon inserts into a large number of sites in the T4 genome, probably with a preference for certain regions. The transposon insertions in four strains were analysed by DNA sequencing using primers that hybridize to each end of the transposon and read out into the T4 genome. In each case, a 9 bp T4 target sequence had been duplicated and the insertions had occurred exactly at the IS50 ends of the transposon, demonstrating that bona fide transposition had occurred. Finally, the transposon insert strains were screened on the TabG Escherichia coli strain, which inhibits the growth of T4 motA mutants, and a motA transposon insert strain was found.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 52
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 53
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The rfb (O antigen) gene cluster of group C2 Salmonella differs from that of group B in a central region of 12.4kb: we report the sequencing of this region of strain M67 (group C2) and a subsequent comparison with the central region of strain LT2 (group B). We find a block of seven open reading frames unique to group C2 which encode the O antigen polymerase (rfc) and the transferases responsible for assembly of the group C2 O antigen. The remaining rfb genes are common to strains M67 and LT2, but rfbJ (GDP-abequose synthase) and rfbM and rfbK (GDP-mannose synthesis), which are immediately adjacent to the central region, are highly divergent. All these genes have a low G+C content and appear to have been recent additions to Salmonella enterica. We discuss the evolutionary significance of the arrangement and divergence of the genes in the polymorphism of the rfb cluster.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 54
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The 90-kilobase (kb) virulence plasmid of Salmonella typhimurium is responsible for invasion from the intestines to mesenteric lymph nodes and spleens of orally inoculated mice. We used Tn5 and aminoglycoside phosphotransferase (aph) gene insertion mutagenesis and deletion mutagenesis of a previously identified 14-kb virulence region to reduce this virulence region to 7.8kb. The 7.8-kb virulence region subcloned into a low copy-number vector conferred a wild-type level of splenic infection to virulence plasmid-cured S. typhimurium and conferred essentially a wild-type oral LD50. Insertion mutagenesis identified five loci essential for virulence, and DNA sequence analysis of the virulence region identified six open reading frames. Expected protein products were identified from four of the six genes, with three of the proteins identified as doublet bands in Escherichia coli minicells. Three of the five mutated genes were able to be complemented by clones containing only the corresponding wild-type gene. Only one of the five deduced amino acid sequences, that of the positive regulatory element, SpvR, possessed significant homology to other proteins. The codon usage for the virulence genes showed no codon bias, which is consistent with the low levels of expression observed for the corresponding proteins. Consensus promoters for several different sigma factors were identified upstream of several of the genes, whereas only consensus Rho-dependent termination sequences were observed between certain of the genes. The operon structure of this virulence region therefore appears to be complex. The construction of the cloned 7.8-kb virulence region and the determination of the DNA sequence will aid in the further genetic analysis of the five plasmid-encoded virulence genes of S. typhimurium.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 55
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: DNA helicases are ubiquitous enzymes that catalyse the unwinding of duplex DNA during replication, recombination and repair. These enzymes have been studied extensively; however, the specific details of how any helicase unwinds duplex DNA are unknown. Although it is clear that not all helicases unwind duplex DNA in an identical way, many helicases possess similar properties, which are thus likely to be of general importance to their mechanism of action. For example, since helicases appear generally to be oligomeric enzymes, the hypothesis is presented in this review that the functionally active forms of DNA helicases are oligomeric. The oligomeric nature of helicases provides them with multiple DNA-binding sites, allowing the transient formation of ternary structures, such that at an unwinding fork, the helicase can bind either single-stranded and duplex DNA simultaneously or two strands of single-stranded DNA. Modulation of the relative affinities of these binding sites for single-stranded versus duplex DNA through ATP binding and hydrolysis would then provide the basis for a cycling mechanism for processive unwinding of DNA by helicases. The properties of the Escherichia coli DNA helicases are reviewed and possible mechanisms by which helicases might unwind duplex DNA are discussed in view of their oligomeric structures, with emphasis on the E. coli Rep, RecBCD and phage T7 gene 4 helicases.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 56
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Understanding the mechanism of glucose repression in yeast has proved to be a difficult and challenging problem. A multitude of genes in different pathways are repressed by glucose at the level of transcription. The SUC2 gene, which encodes invertase, is an excellent reporter gene for glucose repression, since its expression is controlled exclusively by this pathway. Genetic analysis has identified numerous regulatory mutations which can either prevent derepression of SUC2 or render its expression insensitive to glucose repression. These mutations allow us to sketch the outlines of a pathway for general glucose repression, which has several key elements: hexo-kinase PII, encoded by HXK2, which seems to play a role in the sensing of glucose levels; the protein kinase encoded by SNF1, whose activity is required for derepression of many glucose-repressible genes; and the MIG1 repressor protein, which binds to the upstream regions of SUC2 and other glucose-repressible genes. Repression by MIG1 requires the activity of the CYC8 and TUP1 proteins. Glucose repression of other sets of genes seems to be controlled by the general glucose repression pathway acting in concert with other mechanisms. In the cases of the GAL genes and possibly CYC1, regulation is mediated by a cascade in which the general pathway represses expression of a positive transcriptional activator.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 57
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In Escherichia coli, chemotactic sensory transduction is believed to involve phosphoryl transfer for excitation, and changes in receptor methylation for adaptation. In Bacillus subtilis, changes in degree of receptor methylation do not bring about adaptation. Novel methylation reactions are believed to be involved in excitation in B. subtillis. The main chemotaxis proteins of E. coli—CheA, CheB, CheR, CheW and CheY—are present in B. subtilis but play somewhat different roles in the two organisms. Several unique chemotaxis proteins are also present in B. subtilis. Some of the properties of B. subtilis chemotaxis are also seen in Halobacterium halobium, suggesting that there may be a similar underlying mechanism that predates the evolutionary separation of the bacteria from the archaea and eucarya.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 58
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Chlamydia trachomatis major outer membrane protein (MOMP) is the quantitatively predominant surface protein which has important functional, structural and antigenic properties. We have cloned and overexpressed the MOMP in Escherichia coli The MOMP is surface exposed in C. trachomatis and capable of eliciting protective antibodies in infected hosts, and therefore has potential as a candidate vaccine to prevent infection with this significant human pathogen. The recombinant MOMP clone, L2rMOMP, contained the entire MOMP gene including the encoded leader sequence. Large quantities of chlamydial MOMP were expressed, some of which was processed and translocated to the E. coli surface. Surface localization of the MOMP was demonstrated by the binding of anti-MOMP monoclonal antibodies to the surface of the induced clone, and was visualized by fluorescence and electron microscopy. The induction of MOMP expression had a rapidly lethal effect on the L2rM0MP E. coli clone. Although no genetic system exists for Chlamydia, development of a stable, inducible E. coli done which overexpresses the chlamydial MOMP permits a study of the biological properties of the MOMP, including the contribution of the MOMP variable segments to the topographical interactions which determine the antigenic structure responsible for human immune response.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 59
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Many natural DNA sequences are restricted in Escherichia coli K-12, not only by the classic Type I restriction system EcoK, but also by one of three modification-specific restriction systems found in K-12. The McrBC system is the best studied of these. We infer from the base composition of the mcrBC genes that they were imported from an evolutionarily distant source. The genes are located in a hypervariable cluster of restriction genes that may play a significant role in generation of species identity in enteric bacteria. Restriction activity requires the products of two genes for activity both in vivo and in vitro. The mcrB gene elaborates two protein products, only one of which is required for activity in vitro, but both of which contain a conserved amino acid sequence motif identified as a possible GTP-binding site. The mcrC gene product contains a leucine heptad repeat that could play a role in protein-protein interactions. McrBC activity in vivo and in vitro depends on the presence of modified cytosine in a specific sequence context; three different modifications are recognized. The in vitro activity of this novel multi-subunit restriction enzyme displays an absolute requirement for GTP as a cofactor.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 60
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Turnover of the chloramphenicol acetyltransferase (cat) messenger RNA in Escherichia coli was investigated by analysis of cellular mRNA decay intermediates and the transcript sequence. Analysis of the sequence has revealed the presence of a repetitive extragenic palindromic (REP) element at the 3′ end of the transcript as well as several 5′-UUAU-3′ sequences, two elements which have roles in modulating turnover of other E. coli mRNAs. For cat mRNA, however, removal of the REP sequence has no effect on the half-life of the transcript, indicating that the REP sequence does not stabilize the upstream region of this message. Results from mapping of the mRNA decay products by several techniques suggest that the message is instead subject to endonucleolytic attack at five sites 5′ of the REP element. The sequence UUAU is present at three of these five sites. It also appears that the cat mRNA is sequentially cleaved in a 3′ to 5′ direction during turnover of this mRNA in vivo. A model for cat mRNA turnover is discussed.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 61
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A method is described to determine simultaneously the effect of any changes in the ribosome-binding site (RBS) of mRNA on translational efficiency in Bacillus subtilis and Escherichia coli in vivo. The approach was used to analyse systematically the influence of spacing between the Shine-Dalgarno sequence and the initiation codon, the three different initiation codons, and RBS secondary structure on translational yields in the two organisms. Both B. subtilis and E. coli exhibited similar spacing optima of 7–9 nucleotides. However, B. subtilis translated messages with spacings shorter than optimal much less efficiently than E. coli. In both organisms, AUG was the preferred initiation codon by two- to threefold. In E coli GUG was slightly better than (JUG while in B. subtilis UUG was better than GUG. The degree of emphasis placed on initiation codon type, as measured by translational yield, was dependent on the strength of the Shine-Dalgarno interaction in both organisms. B. subtilis v/as also much less able to tolerate secondary structure in the RBS than E. coli. While significant differences were found between the two organisms in the effect of specific RBS elements on translation, other mRNA components in addition to those elements tested appear to be responsible, in part, for translational species specificity. The approach described provides a rapid and systematic means of elucidating such additional determinants.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 62
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The xcp genes are required for the secretion of most extracellular proteins by Pseudomonas aeruginosa. The products of these genes are essential for the transport of exoproteins across the outer membrane after they have reached the periptasm via a signal sequence-dependent pathway. To date, analysis of three xcp genes has suggested the conservation of this secretion pathway in many Gram-negative bacteria. Furthermore, the xcpA gene was shown to be identical to pilD, which encodes a peptidase involved in the processing of fimbrial (pili) subunits, suggesting a connection between pili biogenesis and protein secretion. Here the nucleotide sequences of seven other xcp genes, designated xcpR to -X, are presented. The N termini of four of the encoded Xcp proteins display similarity to the N-termini of type IV pili, suggesting that XcpA is involved in the processing of these Xcp proteins. This could indeed be demonstrated in vivo. Furthermore, two other proteins, XcpR and XcpS, show similarity to the PilB and PilC proteins required for fimbriae assembly. Since XcpR and PilB display a canonical nucleotide-binding site, ATP hydrolysis may provide energy for both systems.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 63
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Subtilisins are extracellular sery l-proteases produced by bacilli (Markland and Emil, 1971). In addition to signal sequences, these proteases have N-terminal extensions (pro-regions) which have also been identified in several other proteases (Silen et al., 1988; Vasantha et al., 1984; Polhner et al., 1987; Henderson et al., 1987; Yanagida et al., 1986; Takagi et al., 1985). The pro-region holds the pro-protease associated with the membrane and release of the protease takes place as a result of pro-region removal by autocatalytic processing (Egnell and Flock, 1991).In this report we describe the construction of four deletion-mutations in the gene encoding subtilisin Carlsberg at the junction between the pro-region and mature subtilisin Carlsberg. We found that the introduction of different deletions abolished the ability of subtilisin to undergo autocatalytic cleavage of the pro-region in cis, whereas cleavage by exogenous subtilisin could still occur in trans. Point mutations were also introduced in positions -5 to +4 around the pro-region and native subtilisin cleavage site. Processing of pro-subtilisin with the point mutations showed that the autocatalytic cleavage and recognition of this junction of the subtilisin Carlsberg pro-region is independent of the amino acid sequence around the cleavage site.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 64
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The promoter region of the agarase gene (dagA) of Streptomyces coelicolor A3(2) is complex; it consists of four distinct promoters with different -10 and -35 regions. We report the isolation of a form of RNA polymerase that mediates transcription in vitro from the dag Ap4 promoter. The core components of this RNA polymerase are associated with a polypeptide of c. 66 kDa; holoenzyme reconstitution experiments show that the 66 kDa polypeptide functions as a sigma factor that directs transcription from the dag Ap4 and Bacillus subtilis veg promoters in vitro. Alignment of the DNA sequences of these two promoters shows that they have bases in common in the -10 and -35 regions and that these sequences are similar to those observed for the major RNA polymerases of other bacteria. N-terminal amino acid sequence analysis of the 66 kDa polypeptide revealed it to be the product of the hrdB gene. Previous experiments showed that the predicted amino acid sequence of the hrdB gene product is very similar to the major sigma factors of other bacteria and suggested that disruption of the hrdB gene is lethal. These observations together lead to the conclusion that we have isolated the major RNA polymerase of Streptomyces coelicolor A3(2).We have developed an improved protocol for the renaturation of sigma factors that have been Isolated by preparative sodium dodecyl sulphate/polyacrylamide gel electrophoresis (SDS-PAGE). This method involves renaturing the polypeptide in the presence of the bacterial chaperonin GroEL. We expect this protocol to find general application for renaturation of other polypeptides that have been subjected to SDS-PAGE.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 65
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The unit-copy P1 plasmid depends for stability on a plasmld-encoded partition region called par, consisting of the parA and parB genes and the parS site. ParA is absolutely required for partition, but its partition-critical role is not known. Purified ParA protein is shown to possess an ATPase activity in vitro which is specifically stimulated by purified ParB protein and by DNA. ParA is responsible for regulation of expression of parA and parB, and purified ParA has an ATP-dependent, site-specific DNA binding activity which recognizes a sequence that overlaps the parA promoter. The rote of the ATP-dependence of the binding activity, as well as other possible functions of the ATPase activity in partition, is discussed.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 66
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Full elastolytic activity in Pseudomonas aeruginosa is a result of the combined activities of elastase, alkaline proteinase, and the lasA gene product, LasA. The results of this study demonstrate that an active fragment of the LasA protein which is isolated from the culture supernatant fraction is capable of degrading elastin in the absence of elastase, thus showing that LasA is a second elastase produced by this organism. In addition, it is shown that LasA-mediated enhancement of elastotysis results from the separate activities of LasA and elastase upon elastin. The LasA protein does not affect the secretion or activation of a proelastase as previously proposed in other studies. Furthermore, LasA has specific proteolytic capability, as demonstrated by its ability to cleave β-casein. Preliminary analysis of β-casein cleavage in the presence of various protease inhibitors suggests that LasA may be classified as a modified serine protease.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 67
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Mycoplasma pulmonis is a murine pathogen that causes chronic respiratory disease in laboratory rats and mice. Several examples of high-frequency phenotypic switching have been reported for M. pulmonis, the molecular basis of which is unknown. We report here that during growth the M. pulmonis chromosome undergoes DNA rearrangements at a high frequency. Some of the rearrangements we examined correlated with changes in the susceptibility of the cells to mycoplasma virus P1, an example of phenotypic switching involving changes in surface antigen structure. Other rearrangements, unrelated to phenotypic switching, involved a DNA element present in the chromosome in multiple copies. The high level of DNA recombination that occurred in M. pulmonis indicates that this may be one of the most variable genomes studied to date. High levels of DNA recombination may contribute to the unusually high rate of evolution that mycoplasmas are thought to be undergoing. Understanding the molecular basis for this phenomenon may provide an insight into the chronic nature of many mycoplasmal infections.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 68
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The gene product of F tral is a bifunctional protein which nicks and unwinds the F plasmid during conjugal DNA transfer. Further biochemical characterization of the Tral protein reveals that it has a second, much lower, Km for ATP hydrolysis, in addition to that previously identified. Measurement of the single-stranded DNA-stimulated ATPase rate indicates that there is co-operative interaction between the enzyme monomers for maximal activity. Furthermore, 18O-exchange experiments indicate that Tral protein hydrolyses ATP with, at most, a low-level reversal of the hydrolytic step during each turnover.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 69
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The photosynthetic apparatus of Rhodobacter sphaeroides is comprised of three types of pigment-protein complex: the photochemical reaction centre and its attendant LH1 and LH2 light-harvesting complexes. To augment existing deletion/insertion mutants in the genes coding for these complexes we have constructed two further mutants, one of which is a novel double mutant which is devoid of all three types of complex. We have also constructed vectors for the expression of either LH1, LH2 or reaction-centre genes. The resulting system allows each pigment-protein complex to be studied either as part of an intact photosystem or as the sole complex in the cell. In this way we have demonstrated that reaction centres can assemble independently of either light-harvesting complex in R sphaeroides. In addition, the isolation of derivatives of the deletion/insertion mutants exhibiting spontaneous mutations in carotenoid biosynthesis provides an avenue for examining the role of carotenoids in the assembly of the photo-synthetic apparatus. We show that the LH1 complex is assembled regardless of the carotenoid background, and that the type of carotenoid present modifies the absorbance of the LH1 bacteriochlorophylls.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 70
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: An improved method for allele replacement in Pseudomonas aeruginosa was developed. The two main ingredients of the method are: (i) novel ColE1-type cloning vectors derived from pBR322 and pUC19; and (ii) a family of cassettes containing a portable oriT, the sacB gene from Bacillus subtilis as a counter-selectable marker, and a chloramphenicol-resistance gene allowing positive selection of both oriT and sacB. Introduction of plasmid-borne DNA into the chromosome was achieved in several steps. The DNA to be exchanged was first cloned into the new ColE1-type vectors. After insertion of the oriT and sacB sequences, these plasmid were conjugally transferred into P. aeruginosa and plasmid integrants were selected. Plating on sucrose-containing medium allowed positive selection for both plasmid excision and curing since Pseudomonas aeruginosa strains containing the sacB gene in single- or multiple copy were highly sensitive to 5% sucrose in rich medium. This procedure was successfully used to introduce an agmR mutation into P. aeruginosa wild-type strain PA01 and should allow the exchange of any DNA segment into any non-essential regions of the P. aeruginosa chromosome.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 71
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Most group A streptococcal strains are able to bind immunoglobulin (lg) in a non-immune manner, and the majority of these strains bind both IgA and IgG. Using molecular cloning and immunochemical techniques, we have purified and characterized the Ig Fc-receptors expressed by four such strains. Two of the strains express a novel type of receptor, designated protein Sir, which binds IgA and IgG of all subclasses, and therefore has broader reactivity than any Fc-receptor previously described. The other two strains express protein Arp, a receptor that binds IgA of both subclasses, and also binds potyclonal IgG weakly. Characterization of the weak IgG-binding ability of protein Arp shows that it binds only some monoclonal IgG proteins, in particular those of the IgG3 subclass. The four strains studied here were unexpectedly found to also express a second Ig-receptor, called protein Mrp, encoded by a gene closely linked to the gene for the first receptor. The Mrp protein does not bind IgA, but it binds IgG molecules of the IgG1, IgG2 and tgG4 subclasses, and it also binds fibrinogen. Binding of fibrinogen has been reported to be a characteristic property of streptococcal M proteins, which suggests that the Mrp protein may be an M protein that also binds Ig. Taken together, all available evidence now indicates that most strains of group A streptococci express two different Ig-binding proteins, encoded by closely linked genes.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 72
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: As an approach for studying how SecY, an integral membrane protein translocation factor of Escherichia coli, interacts with other protein molecules, we isolated a dominant negative mutation, secY-d1, of the gene carried on a plasmid. The mutant plasmid severely inhibited export of maltose-binding protein and less severely of OmpA, when introduced into sec+ cells. It inhibited growth of secY and secE mutant cells, but not of secA and secD mutant cells or wild-type cells. The mutation deletes three amino acids that should be located at the interface of cytopiasmic domain 5 and transmembrane segment 9. We also found that some SecY-PhoA fusion proteins that lacked carboxy-terminal portions of SecY but retain a region from periplasmic domain 3 to transmembrane segment 7 were inhibitory to protein export. We suggest that these SecY variants are severely defective in catalytic function of SecY, which requires cytoplasmic domain 5 and its carboxy-terminal side, but retain the ability to associate with other molecules of the protein export machinery, which requires the central portion of SecY; they probably exert the ‘dominant negative’ effects by competing with normal SecY for the formation of active Sec complex. These observations should provide a basis for further genetic analysis of the Sec protein complex in the membrane.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 73
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A new class of Bacillus thuringiensisδ-endotoxins, or insecticidal control proteins (ICPs), is defined by an apparently cryptic protein with a unique primary structure and novel entomocidal specificity for certain coleopteran and lepidopteran species. The discovery of a new group of ICPs will extend the use of this natural insecticide in integrated pest-management systems.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 74
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The translational roles of the Shine-Dalgarno sequence, the initiation codon, the space between them, and the second codon have been studied. The Shine Dalgarno sequence UAAGGAGG initiated translation roughly four times more efficiently than did the shorter AAGGA sequence. Each Shine-Dalgarno sequence required a minimum distance to the initiation codon in order to drive translation; spacing, however, could be rather long. Initiation at AUG was more efficient than at GUG or UUG at each spacing examined; initiation at GUG was only slightly better than UUG. Translation was also affected by residues 3′ to the initiation codon. The second codon can influence the rate of initiation, with the magnitude depending on the initiation codon. The data are consistent with a simple kinetic model in which a variety of rate constants contribute to the process of translation initiation.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 75