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  • 1985-1989  (410,744)
  • 1975-1979  (270,112)
  • 1970-1974  (227,045)
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  • 1
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    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
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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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  • 5
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    Greenwich, Conn. : JAI Press.
    Associated volumes
    Keywords: Cells
    Notes: Please search for single volumes in "Reihe (alphabetisch)" or "Reihe (Stichwort)"
    ISSN: 0898-8455
    Subsequent Title: Advances in molecular and cell biology
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 5 (1989), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: This paper describes LEW (learning by watching), an implementation of a novel learning technique, and discusses its application to the learning of plans. LEW is a domain-independent learning system with user-limited autonomy that is designed to provide robust performance in realistic knowledge acquisition tasks in a variety of domains. It partly automates the knowledge acquisition process for different knowledge types, such as concepts, rules, and plans. The inputs to the system, which we call cues, consist of an environmental component and of pairs containing a problem and its solution. Unlike traditional forms of “learning from examples”, in which the system uses the teacher's answer to improve the result of a prior generalization of an example, LEW treats the problem-solution or question-answer instances, i. e., the cues themselves, as the basic units for generalization.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Computational intelligence 5 (1989), S. 0 
    ISSN: 1467-8640
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Computer Science
    Notes: Most shape-from-shading methods assume that surface reflectance is constant within large image regions. This assumption is violated in natural scenes with objects made from different materials. We present a more general method for recovering shape from shading, assuming that surfaces are smooth and albedo is piecewise constant, as would be the case if a Mondrian image was painted on a smooth curved surface. Our method is based on combining Brooks and Horn's method for shape recovery with the recovery of albedo using stochastic relaxation.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Teaching statistics 11 (1989), S. 0 
    ISSN: 1467-9639
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mathematics
    Notes: The author's experiences in buying a caravan led him to some interesting statistical work which could be of use in teaching.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The induction of several amino acid decarboxylases under anaerobic conditions at low pH has been known for many years, but the mechanism associated with this type of regulation has not been elucidated. To study the regulation of the biodegradative arginine and lysine decarboxylases of Escherichia coli K12, Mudlac fusions to these genes were isolated. Mudlac fusion strains deficient for lysine decarboxylase or arginine decarboxylase were identified using decarboxylase indicator media and analysed for their regulation of β-galactosidase expression. The position of the Mud-lac fusion in lysine decarboxylase-deficient strains has been mapped to the cadA gene at 93.7 minutes, while the Mudlac fusions exhibiting a deficiency in the inducible arginine decarboxylase have been mapped to 93.4 minutes.
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  • 10
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The gene encoding monophosphatidylinositol inositol phosphohydrolase (PI-specific phospholipase C, PI-PLC) of Bacillus thuringiensis was cloned in Staphylococcus carnosus TM300. The complete coding region comprises 987 base pairs corresponding to a precursor protein of 329 amino acids (molecular weight, 38095). The NH2-terminal sequence of the purified enzyme from Escherichia coli indicated that the mature PI-PLC consists of 299 amino acid residues with a molecular weight of 34586. Polyacrylamide gel electrophoresis revealed the same molecular weight for the purified enzyme isolated from the DNA-donor strain of B. thuringiensis and from the E. coli clone. By computer analysis, the secondary structure was predicted. The enzyme from the E. coli recombinant shows no activity on other phospholipids and sphingo-myelin. The cleaving specifity of PI-PLC was examined by thin layer chromatography.
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  • 11
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The ospA and ospB genes encode the major outer membrane proteins of the Lyme disease spirochaete Borrelia burgdorferi. The deduced translation products from the ospA and ospB genes were: (OspA) 273 amino acids long with a molecular weight of 29334, and (OspB) 296 amino acids long with a molecular weight of 31739. The two Osp proteins showed a great degree of sequence similarity indicating a recent evolutionary event. Molecular analysis and sequence comparison of OspA and OspB with other proteins revealed a sequence similarity to the signal peptides of prokaryotic lipoproteins. These are the first sequences from Borrelia and provide interesting data on the evolutionary relationship between spirochaetes and other species as well as providing potential for spirochaete diagnostics and vaccines.
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  • 12
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The nucleotide sequence has been determined for the Streptococcus mutans wall-associated protein A (wapA) gene from serotype c strains Ingbritt and GS5. The nucleotide sequence for each wapA gene was virtually identical, although the gene from strain GS5 contained a 24 base pair deletion. A 29 amino acid signal peptide was specified by each wapA gene with a mature protein of 424 amino acids (Mr, 45276) for strain Ingbritt and 416 amino acids (Mr, 44846) for strain GS5. In the C-terminal region of the wall-associated protein A, considerable sequence similarity was found with the membrane anchor region of proteins from other Gram-positive organisms such as the group A streptococcal M protein and the group G streptococcal IgG binding protein. Adjacent to the proposed membrane anchor is a highly hydrophilic region which may span the cell wall; both sequence data and experimental evidence indicate the existence of a region immediately outside the wall at which proteolytic cleavage occurs to release antigen A of Mr 29000 into the culture supernatant. Thus, the wall-associated protein A is a precursor of the 29000 Mr antigen A.
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  • 13
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Cells of the thermoacidophilic bacterium Bacillus acidocaldarius express a high-affinity K+-uptake system when grown at low external K+. A vanadate-sensitive, K+ - and Mg2+ -stimulated ATPase was partially purified from membranes of these cells by solubilization with a non-ionic detergent followed by ion-exchange chromatography of the extract. Combinations of non-denaturing and denaturing electrophoretic separation methods revealed that the ATPase complex consisted of three subunits with molecular weights almost identical to those of the KdpA, B and C proteins, which together form the Kdp high-affinity, K+ -translocating ATPase complex of Escherichia coli. The affinity of the partially purified ATPase from B. acidocaldarius for its substrates K+ (Km 2–3 μM) and ATP (Km 80 μM), its stimulation by various divalent cations, and its inhibition by vanadate (Ki 1–2 μM), bafilomycin A1 (Ki, 20 μM), DCCD (Ki 200 μM) or Ca2+ were also similar to those of the E coli enzyme, indicating that the two K+ -translocating ATPases have almost identical properties.
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  • 14
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Yop proteins of Yersinia are important virulence determinants. The Yop1 protein sequences of Yersinia pestis, Yersinia pseudotuberculosis, and two Yersinia enterocolitica serotypes, O:3 and O:8, deduced from the nucleotide sequences of the corresponding yopA genes, were compared. Most differences were found in the hydrophilic domains of the proteins, whereas the hydrophobic domains were conserved. The amino acid sequences revealed a signal sequence 25 amino acids long. No cysteine residues were present, even though Yop1 forms a polymeric structure.The transcription startpoint of yop4 was determined by primer extension. The coding region and transcription startpoint were separated by a leader sequence 270 nucleotides long. The yopA promoter sequence of Y. pestis is identical to the corresponding sequence of Y. pseudotuberculosis and transcription studies revealed that this promoter is active in Y. pestis. Thus, the inability of Y. pestis to express the Yop1 protein is due to a single base pair deletion In the coding region of the yopA gene of Y. pestis (Rosqvist et al., 1988).
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  • 15
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The DNA sequence of a 3.6kb region downstream of the nagB gene (encoding glucosamJne-6-PO4-deaminase) in Escherichia coli has been determined. Three open reading frames, which are subsequently referred to as nagA, nagC and nagD, were detected in this sequence. Genetic complementation and enzyme assays have shown that the first of these, nagA, encodes N-acetyl glucosamine-6-phosphate deacetylase. Growth on N-acetyl glucosamine induces the synthesis of a 1900 nucleotide long transcript which covers just nagE, encoding EIINag which is transcribed divergently from nagB, and of a 4200 nucleotide long transcript which covers all four ORFs of the nagB, A, C, D operon. More mRNA corresponding to nagB and nagA is detected than that corresponding to the distal genes, nagC and nagD. Considerable amounts of the induced mRNA are truncated molecules having their 3’ends after nagB and after nagA. Multiple 3′ RNA ends have been mapped after nagD and seem to correspond to the ends of transcripts stabilized by mRNA secondary structure (REP sequences) rather than transcription termination sites. A second promoter producing napD-specific transcripts has been mapped just in front of the nagD gene.
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  • 16
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The proline catabolism gene cluster of Aspergillus nidulans was cloned using a ‘brute force’ technique which detects clones hybridizing to restriction fragments overlapping chromosomal rearrangements. A number of deletion mutations and a translocation mutation in the cluster have been physically mapped, and an excellent correlation between the genetic and physical maps was established. Transcripts have been identified and orientated for each of the four genes of the cluster. All are monocistronic by size. All of the transcripts, including that of the regulatory gene prnA, are inducible. Using deletion endpoints and mRNA sizes, approximate gene positions on the physical map have been determined. Finally, the relationship between genetic and physical distance across the cluster has been estimated at 3-4 kilobases per centiMorgan.
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  • 17
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The level of DNA supercoiling is crucial for many cellular processes, Including gene expression, and is determined, primarily, by the opposing actions of two enzymes: topoisomerase I and DNA gyrase. Escherichia coli strains lacking topoisomerase I (topA mutants) normally fail to grow in the absence of compensatory mutations which are presumed to relax DNA. We have found that, in media of low osmolarity, topA mutants are viable in the absence of any compensatory mutation, consistent with the view that decreased extracellular osmolarity causes a relaxation of cellular DNA. At higher osmolarity most compensatory mutations, as expected, are in the gyrA and gyrB genes. The only other locus at which compensatory mutations arise, designated toc, is shown to involve the amplification of a region of chromosomal DNA which includes the tolC gene. However, amplification of tolC alone is insufficient to explain the phenotypes of toc mutants. tolC insertion mutations alter the distribution of plasmid topoisomers in vivo. This effect is probably indirect, possibly a result of altered membrane structure and an alteration in the cell's osmotic barrier. As tolC is a highly pleiotropic locus, affecting the expression of many genes, it is possible that some of the TolC phenotypes are a direct result of this topological change. The possible relationship between toe and tolC mutations, and the means by which tolC mutations might affect DNA supercoiling, are discussed.
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  • 18
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The region of the antibiotic resistance plasmid R100 that encodes the plasmid-specific transfer gene traM has two tandemly aligned promoters separated by 145 nucleotides. The principal transcripts are 705 and 562 nucleotides long. Minor transcripts are 1550 and 1700 nucleotides long. The 705-base transcript appears to encode an 11 kD traM protein. The 562-base transcript does not encode a detectable protein. When sub-cloned on short fragments, the promoter for the 562-base transcript initiates efficiently but that for the 705 site does not. The 3′ ends of the 705 and 562 base transcripts end inside the traJ ORF. Thus they provide additional sense RNA to compete with traJ for finP, the antisense translational regulator of traJ. A model is proposed for the participation of these sense and antisense transcripts in the control of expression of the traJ gene.
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  • 19
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Two regions of homology to Anabaena nifH (nitrogenase Fe protein) were detected in the total DNA of the thermophilic nitrogen-fixing archaebacterium Methanococcus thermolithotrophicus. A 2.8 kb Hindlll fragment carrying one of these regions was previously cloned and shown to contain a nifH gene (Souillard et al., 1988) now referred to as 0RFnifH2. A 3.4kb Pstl fragment and an overlapping 3.B kb BglU fragment, containing the second region of homology, were cloned, and a DNA region of 4073bp was sequenced. It contained four complete open reading frames (ORFs) (ORFnifH1, ORF105, ORF128, ORFnifD) and two truncated ORFs (ORFnifK and ORF96). Five ORFs were transcribed in the same direction in the order of ORFnifH1-ORF105-ORF128-ORFnifD-ORFnifK. ORFnifH1, ORFnifD and ORFnifK were assigned from their similarity to eubacterial nifH and nifDK (nitrogenase MoFe protein) genes. Transcription studies showed that ORFnifH1 and ORFnifD were expressed only under nitrogen-fixation conditions, whereas no ORFnifH2 mRNA was detected under the same conditions. A DNA probe containing ORFnifH1 hybridized with a 1.8 kb mRNA, as detected by a Northern blotting experiment. A transcriptional start site was localized 87 and 88 bp upstream from the ATG codon of ORFnifH1, This site is preceded, 21 bp upstream, by the sequence 5′-TTTATATA-3′ already found at the same position in several archaebacterial promoters. ORFnifH1 mRNA was too small to encode ORFnifDK. This was confirmed by the fact that another transcription start site was localized 85bp upstream from the ATG codon of ORFnifD.
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  • 20
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The feasibility of using a β-lactamase fusion approach for maximizing the levels of periplasmic or membrane-bound proteins expressed in Escherichia coli was investigated. The coding region for mature TEM β-lactamase was fused after the signal peptide and amino-terminal portion of the coding region of a weakly expressed periplasmic protein, PBP3*. The resultant plasmid was mutagenized and transformants expressing increased levels of ampicillin resistance were selected. The PBP3*gene of the unmutagenized I β-lactamase fusion plasmid, and of two mutant derivatives encoding increased ampicillin resistance, were then reassembled and the latter constructs were found to express increased levels of PBP3*. The applications of a β-lactamase fusion approach in monitoring and optimizing levels of extracytoplasmic gene products expressed in E. coli are considered.
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  • 21
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A 60 kbp region of the Bacillus subtilis chromosome encompassing the genes concerned with teichoic acid biosynthesis has been subjected to physical analysis. No homo logy was detected by Southern hybridization between DNA segments encoding the tag genes of strain 168, concerned with polyglycerol phosphate (poly(groP)) biosynthesis, and the tar genes of strain W23, concerned with polyribitol phosphate (poly-(rboP)) biosynthesis. Analysis of 168/W23 interstrain hybrids that incorporate poly(rboP) instead of poly-(groP) into their cell walls revealed that, in every case, Integral substitution of the W23 tar genes for the 168 tag genes had occurred. Interstrain hybrids of the‘W23-like’type have inherited larger segments of W23 DNA than interstrain hybrids of the‘mixed’type. The tag and tar genes are located at equivalent positions on the chromosomes of strains 168 and W23, behaving, in genetic crosses, like an allelic pair. They provide the first example of a pseudo-allelic relationship between non-homologous genes in B. subtilis.
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  • 22
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Elaboration of a capsule composed of one of a range of acidic polysaccharides is a common feature of many bacteria, particularly those capable of causing serious infections in humans. Biochemical and genet-cal analyses of capsule biogenesis in Escherichia coli are beginning to reveal new aspects of polysaccharide biosynthesis. Genes have been identified which are thought to encode products responsible for the trans-location of these high molecular-weight polysaccharides across the cytoplasmic and outer membranes, and the organization of exported polysaccharide into a capsule. Their further analysis should provide new insights into membrane biology, particularly since the genes in question are absent from the often used laboratory strains of E. coli. Genetic analysis of capsule diversity is beginning to suggest possible mechanisms for the generation of the structural diversity of polysaccharides.
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  • 23
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Salmonella species are facultative intracellular parasites, capable of penetrating (invading), surviving, and often multiplying within diverse eukaryotic cell types, including epithelial and phagocytic cells. These processes are essential for virulence, and involve both bacterial and host cell products. The use of cultured eukaryotic cells and other model systems has facilitated the study of bacterial-host cell interactions, and has led to a better understanding of the genetic and molecular basis of Salmonella pathogenicity.
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  • 24
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The relF gene in Escherichia coli is related to the hok gene on plasmid R1. Both genes encode small proteins which, when overexpressed In E. coli lead to collapse of the membrane potential and cell death. A third gene, designated gef, which encodes a homologous cell-toxic protein, has been isolated from E. coli DNA. Both gef and relF are transcribed in E. coli and subject to post-transcriptional regulation which, in the case of gef, is coupled to translation of a leader sequence. The finding of homologous sequences in such distantly related bacteria as Agrobacterium and Rhizobium species suggests an important physiological role.
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  • 25
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Pulsed-field gel electrophoresis was used to generate a molecular karyotype of chromosomes from the opportunistic AIDS pathogen, Pneumocystis carinii. P. carinii cysts and trophozoites were isolated from immunosuppressed rats, lysed in situ in agarose blocks, and subjected to orthogonal-field gel electrophoresis (OFAGE) and contour-clamped homogeneous-field gel electrophoresis (CHEF). OFAGE and CHEF gels resolved, respectively, 16 or 20 chromosome bands ranging in size from 0.32-1.5 megabase pairs. Summation of the estimated sizes of these chromosomes suggested a total genome complexity for P. carinii of 8-16 megabase pairs. Homologous probes for the genes encoding the 18S, 5.8S, and 5S ribosomal RNAs were hybridized to filter blots of the pulsed-field gels to map these genes to specific P. carinii chromosomes.
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  • 26
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A gene that codes for a small stable RNA (362 nucleotides) has been sequenced. It is a monocistronic gene, with its own promoter and terminator. It produces a precursor that is about 100 nucleotides longer than the mature RNA with all the extra nucleotides at the 3′ end. The gene contains an open reading frame that corresponds to a small protein 25 amino acids long.
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  • 27
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have characterized a series of amber mutations in the A gene of bacteriophage Mu encoding the phage transposase. We tested different activities of these mutant proteins either in a sup0 strain or in different sup bacteria. In conjunction with the results described in the accompanying paper by Bétermier et al. (1989) we find that the C-terminus of the protein is not absolutely essential for global transposase function, but is essential for phage growth. Specific binding to Mu ends is defined by a more central domain. Our results also reinforce the previous findings (Bétermier et al., 1987) that more than one protein may be specified by the A gene.
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  • 28
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have generated a series of 3’deletions of a cloned copy of the bacteriophage Mu transposase (A) gene. The corresponding truncated proteins, expressed under the control of the λ Pl promoter, were analysed in vivo for their capacity to complement a superinfecting Mu4am phage, both for lytic growth and lysogeny, and for their effect on growth of wild-type Mu following infection or induction of a lysogen. Using crude cell extracts, we have also examined binding properties of these proteins to the ends of Mu. The results allow us to further define regions of the protein important in replicative transposition, establishment of lysogeny and DNA binding.
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  • 29
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A collection of transposon-induced mutants of Rhizobium meliloti 1021 defective in siderophore-mediated iron assimilation were obtained and classified as biosynthetic, transport or regulatory. Several of the mutations were cloned and the adjacent sequences were used to acquire complementing DNA from the wild type. A single genomic region of about 35kb complemented all of the mutants deficient in production of the siderophore.
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  • 30
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Mutants of Escherichia coli defective in the mdoA locus are blocked at an early stage in the biosynthesis of membrane-derived oligosaccharides. The mdoA locus has now been cloned into multicopy plasmids. A 5kb DNA fragment is necessary to complement mdoA mutations. Cells harbouring the mdoA+ plasmid produced three to four times more MDO than wild-type cells. MDO overproduction did not affect the degree of MDO substitution with sn-1-phosphoglycerol residues. The biosynthesis of MDO remained under osmotic control in overproducing strains.
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  • 31
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The 7kb virulence Region-2 of the large (virulence) plasmid in Shigella flexneri 2a encodes several proteins required for invasion of intestinal epithelial cells. Insertion and deletion mutagenesis, DNA subcloning and SDS-polyacrylamide gel electro-phoresis of proteins synthesized in minicells demonstrated five genes in this region. They encode 24, 18, 62 (lpaB), 41 (lpaC) and 37 (lpaD)-kiloDalton (kD) proteins. Complementation of Tn5-induced mutations in Region-2 with the above plasmid constructs indicated that Region-2 consists of two operons and that the three lpa proteins are essential for the virulence phenotype. The transcriptional organization determined by Northern blotting, S1 nuclease protection and the effect of Tn5 insertions on expression of the lpa proteins revealed that Region-2 has three promoters that transcribe RNAs of 4.0, 4.5 and 7.5kb. The 4.0 kb RNA was the transcript for the operon encoding the 24, 18 kD, lpaB and C proteins and the 4.5 kb RNA for the ipsD gene. In addition, the full-length RNA of 7.5 kb which covers Region-2 supplemented full expression of the lpa proteins. The 7663 nucleotides of Region-2 were determined to confirm the five open reading frames encoding 23655, 17755, 62168, 41077 and 36660 Dalton proteins, respectively, and their regulatory sequences.
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  • 32
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Conjugation systems that transfer antibiotic resistance in the absence of detectable plasmids are common in Bacteroides, but the mechanism of transfer is poorly understood. We found that linked transfer of tetracycline (ToR) and clindamycin (CIR) resistance by Bacteroides fragilis strain 1126 is induced by growth in either Tc or Cl. We cloned the transferable TcR locus as a 13 kb fragment on the shuttle vector pPH6 in Escherichia coli and showed that this region expresses TcR in Bacteroides but not E. coli. The TcR gene was mapped to a 3 kb region and the CIR gene was shown not to be present in the 13 kb insert. Homologous TcR genes are found in B. fragilis V479 and 1792. Using pulsed-field electrophoresis, the transferable TcR gene was shown to be physically associated with high molecular-weight DNA, suggesting that it is located on the chromosome. A new TcR shuttle vector. pPH7δ1.1, was constructed to facilitate use of this selective marker in Bacteroides genetics.
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  • 33
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The predicted protein sequence of the nodL gene from Rhizobium leguminosarum was screened against translations of the GenBank DNA sequence database. A very strong homology was found to lacA, which encodes thiogalactoside transferase; homology between NodL and the cysE gene product (serine acetyl transferase) was also found. Comparison of the conserved regions of the three protein sequences indicated a domain that may be an active site of the enzymes.
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  • 34
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Corynebacterium glutamicum fda gene encoding fructose- 1,6-btphosphate (FBP) aldolase has been isolated by complementation of an Escherichia coli mutant. The nucleotide sequence of a 3371 bp chromosomal fragment containing the C. glutamicum fda gene was determined. The N-terminal amino acid sequence of C. glutamicum FBP aldolase identified the correct initiation site for the fda gene, and a molecular weight of 37092 was predicted for the fda polypeptide. S1 nuclease mapping identified the transcriptional start site, and Northern hybridization analysis indicated that the fda gene encodes a single 1.3 kb transcript. The primary structure of C. glutamicum FBP aldolase shows strong homology to class 11 FBP aldolases. Conservation of primary structure was observed between class I and class II aldolases, but several residues essential for catalytic activity in class I aldolases were absent from class II aldolases.
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  • 35
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The cloned Citrobacter freundii ampC β-lactamase is inducible in the presence of its regulatory gene ampR in Escherichia coli (Lindberg et al., 1985). The basal level of expression and inducibility are affected by two E. coli proteins encoded by the closely linked ampD and ampE genes. Deletion of both genes led to constitutive ampR-dependent overproduction of β-lactamase, whereas an out-of-frame deletion in AmpD caused the basal expression to increase twofold. This ampD1 mutant was inducible at lower β-lactam concentrations than the wild type. An IS1 insertion in ampD was polar on ampE expression and increased basal β-lactamase expression 30-fold while mediating a semi-constitutive phenotype. AmpE expressed from a recombinant plasmid in an ampD ampE deletion mutant reduced basal β-lactamase expression to wild-type levels but did not markedly reduce β-lactam resistance since the cells became hyperinducible. in the absence of AmpD, increasing levels of AmpE therefore decrease the basal expression of AmpC β-lactamase in an AmpR-dependent manner. AmpD modulated the response exerted on β-lactamase expression by AmpE. The ampD gene encodes a 20.5kD cytoplasmic protein while the 32.1kD ampE gene product is an integral membrane protein with a likely ATP-binding site between the second and third putative transmembrane region. Since neither AmpD nor AmpE are needed for β-lactam induction and since these proteins could not be covalently labelled by benzylpenicillin, they are not thought to act as β-lactam-binding sensory tranducers. Instead it is suggested that AmpD and AmpE sense the effect of β-lactam action on peptidoglycan biosynthesis and relay this signal to AmpR.
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  • 36
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In clinical isolates of Enterobacter cloacae, resistance to the newer β-lactam antibiotics often results from overproduction of a cephalosporinase encoded by the β-lactam-inducible ampC gene. Regulation of ampC is controlled by the divergently expressed activator gene, ampR, and a second unlinked locus. In this presentation we show that although Escherichia coli has IQst its ampR gene it has retained the second regulatory locus and that this comprises the bicistronic ampDE operon. Genetic and biochemical studies define the ampD gene as encoding a repressor for amp C transcription whereas the ampE gene product is a cytoplasmic membrane protein. Inactivation of the AmpD protein by mutation causes massive overproduction of cephalosporinase which, in E. cloacae, can terminate in therapeutic failure. In contrast, toss of AmpE results in a total block in induction, despite the presence of the activator, AmpR.
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  • 37
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: As a result of a temperature shift-up from 30°C to 42°C, β-lactamase synthesis in Escherichia coli carrying pBR322 ceased transiently, even though the level of β-lactamase mRNA was not altered. pBR328-directed pre-β-lactamase synthesis in an in vitro transcription-translation coupled system was also repressed by incubation at the higher temperature. Translation of the lacZ sequence from the amp translation start signal, inserted into the open reading frame vector pORF1, was also repressed transiently upon the temperature shift-up. Pre-heating of the in vitro coupled system at 45°C specifically reduced its capacity for pre-β-lactamase synthesis. This capacity was restored by the addition of a 160000 × g supernatant prepared from E. coli grown at 30°C, but not by the supernatant from the cells incubated at 42°C. These and other results Indicate that (i) the 160000 × g supernatant contains a heat-labile protein(s) that is required for efficient initiation of the translation of pre-β-lactamase mRNA, and (ii) the heat shock-induced repression of β-lactamase synthesis is due to inactivation of the protein(s) in the 160000 × g supernatant.
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  • 38
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Reverse transcriptase, discovered in 1970 in retroviruses, has until recently been found only in eukaryotic organisms. Recently it was shown to occur in two groups of bacteria: myxobacteria and Escherichia coli. The gene for reverse transcriptase is part of a chromosomal genetic element that codes for the production of a branched DNA-RNA compound. In this compound a single-stranded DNA is connected to RNA at a specific G residue by a 2′-5’phosphodiester linkage. The precursor for the DNA-RNA compound is a folded messenger RNA, in which the specific G residue is the initiation point for reverse transcription. In the final DNA-RNA compound, the portion of the RNA transcribed by reverse transcriptase is eliminated by RNase H. The DNA-RNA compound is present in several hundred copies per cell. Its biological function is unknown at present.
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  • 39
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The phytopathogenic enterobacterium Erwinia chrysanthemi secretes a number of enzymes involved in plant-tissue degradation, notably the five isoenzymes of pectate lyase. We have cloned a region involved in pectate lyase and cellulase secretion by complementation of non-secretory outJ mutants of E. chrysanthemi strain 3937 using the RP4::miniMu plasmid pULB110. The cloned region maps near the ade-22 marker on the E. chrysanthemi 3937 chromosome. An R-prime containing a chromosomal DNA insert of about 30 kb was first obtained; subcloning into pBR325 permitted the isolation of a 4 kb Cial/Sspl fragment able to complement outJ mutations in E. chrysanthemi. The isolation of phoA fusions in this fragment allowed us to determine the direction of transcription of the encoding region, which extends over about 2.5 kb, and demonstrate that this region encodes exported protein(s). When the TnphoA insertions were transferred back into E. chrysanthemi chromosome, the recombined strains no longer secreted pectate lyases or cellulases. Identification of the products encoded by the Cial/Sspl fragment demonstrated that oufJ encodes an 83 kD polypeptide which is processed to an 81 kD polypeptide by cleavage of a signal sequence. The cloned DNA fragment did not endow Escherichia coli with the ability to secrete pectate lyases.
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  • 40
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The nucleotide sequence of a 2.4 kb Dral-EcoRV fragment of pColD-CA23 DNA was determined. The segment of DNA contained the colicin D structural gene (cda) and the colicin D immunity gene (cdi). From the nucleotide sequence it was deduced that colicin D had a molecular weight of 74683D and that the immunity protein had a molecular weight of 10057D. The amino-terminal portion of colicin D was found to be 96% homologous with the same region of colicin B. Both colicins share the same cell-surface receptor, FepA, and require the TonB protein for uptake. A putative TonB box pentapeptide sequence was identified in the amino terminus of the colicin D protein sequence. Since colicin D inhibits protein synthesis, it was unexpected that no homology was found between the carboxy-terminal part of this colicin and that of the protein synthesis inhibiting colicin E3 and cloacin DF13. This could indicate that colicin D does not function in the same manner as the latter two bacteriocins. The observed homology with colicin B supports the domain structure concept of colicin organization. The structural organization of the colicin operon is discussed. The extensive amino-terminal homology between colicins D and B, and the strong carboxy-terminal homology between colicins B, A, and N suggest an evolutionary assembly of colicin genes from a few DNA fragments which encode the functional domains responsible for colicin activity and uptake.
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  • 41
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A gene, pcnB, affecting the copy number of ColE1-related plasmids has been cloned and mapped to 3.6 min on the Escherichia coli chromosome between panD and fhu. The gene encodes a previously un-described 48 kD protein. Several independently isolated mutants exhibiting the same phenotye, reduced copy number, have been shown to be pcnB.
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  • 42
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Haploid recombinant progeny of Phanerochaete chrysosporium ME446, genome compositions of which had been defined by RFLP-mapping, vary in their idiophasic behaviour. This allowed us to formulate a model of the sequence of idiophasic activities. One component of this variation, the amount of lignin peroxidase activity, is independent of the allele distributions of the lignin peroxidase gene clusters, but correlates with the allele distribution of another locus. This locus appears to control the spread of the lignin peroxidase-active state within the idiophasic mycelial mat and may be the mating-type locus. The successful determination of linkage relied on analysis of chromosome intervals rather than linkage to single markers; this approach should be generally useful for analysing quantitative characters by RFLP mapping.
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  • 43
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The expression of Escherichia coli type 1 fimbriae is phase-variable i.e. the bacterial cell is either fimbriated or non-fimbriated. The transition from one state to the other is caused by the change in configuration of an invertible DNA segment harbouring the promoter of the fimA gene. The position of this phase switch is controlled by two proteins, FimB and FimE, which mediate an ‘on’ or ‘off’ configuration of the switch, respectively. In this study, we have investigated how these proteins control the switch by means of fim-lac fusions on low-copy-number plasmids. It was found, by in trans and cis complementation, that the ratio of fimB to fimE and the total concentration of the gene products determine the configuration of the switch as well as the frequency of phase switching. It was also shown that transcription occurs from the promoter located at the phase switch when this is in the ‘off’ configuration. This suggests a regulatory mechanism, since the resulting transcript would be anti-sense to the fimE transcript.
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  • 44
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The nifA gene has been identified between the fixX and nifB genes in the clover microsymbiont Rhizobium leguminosarum biovar trifolii (R.I. bv. trifolii) strain ANU843. Expression of the nifA gene is induced in the symbiotic state and site-directed mutagenesis experiments indicate that nifA expression is essential for symbiotic nitrogen fixation. Interestingly, the predicted R.I. bv. trifolii NifA protein lacks an N-terminal domain that is present in the homologous proteins from R.I. bv. viciae, Rhizobium meliloti, Brady rhizobium japonicum, Klebsiella pneumoniae and all other documented NifA proteins. This indicates that this N-terminal domain is not essential for NifA function in R.I. bv. trifolii.
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  • 45
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The regulation of several genes in response to osmotic and anaerobic stress has been examined. We have demonstrated a clear overlap between these two regulatory signals. Thus, the osmotically induced proU and ompC genes require anaerobic growth for optimum induction while the anaerobically induced tppB gene is also regulated by osmolarity. Furthermore, normal expression of tppB and ompC requires the positive regulatory protein OmpR, yet this requirement can be partially, or even fully, overcome by altering the growth conditions. Finally, the pleiotropic, anaerobic regulatory locus, oxrC, is also shown to affect expression of the osmoticalty regulated proU gene. The oxrC mutation is shown to affect the level of negative supercoiling of plasmid DNA and its effects on gene expression can be explained as secondary consequences of altered DNA topology. We suggest that there is a class of ‘stress-regulated’ genes that are regulated by a common mechanism in response to different environmental signals. Furthermore, our data are consistent with the notion that this regulatory overlap is mediated by changes in DNA supercoiling in response to these environmental stresses.
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  • 46
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Nucleotide sequence analysis of two Mycoplasma hyopneumoniae-derived copies of a repetitive genetic element revealed structural similarities to typical prokaryotic insertion sequences. This is the first such sequence identified in the class Mollicutes. The element spans approximately 1550bp, with 28bp inverted terminal repeats. Two open reading frames occur within the sequence, one potentially encoding a protein with a size-variant alpha-helical domain containing heptameric leucine periodicity. Hybridization data with several strains from each of two mycoplasma species showed that the repetitive sequence is variably distributed within the M. hyopneumoniae and Mycoplasma hyorhinis chromosomes and indicated that in some cases the repeated sequence is contained within a larger genetic element which may be the result of phage or plasmid Insertion.
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  • 47
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have determined the DNA sequences of eight different insertions of IS91 in a specifically engineered recipient plasmid of known DNA sequence (pSU300). The sequences at the termini of IS91 are 5′ -CGAG-TAGG… CCTATCGAT. IS91 inserts specifically 5′ to either one of the tetranucleotides 5′-GAAC or 5′-CAAG, and always in the same relative orientation with respect to the sequence of the target. Except in one special case, no duplications of the recipient DNA were produced at the site of insertion.
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  • 48
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The activation of the Agrobacterium virulence system is known to be induced by certain phenolic compounds. We have tested the vir-inducing ability of fifty compounds, by using a virB-lacZ gene fusion, and analysed the relationship between structure and activity of these compounds. In this way we have identified several new vir-inducers: coniferylalcohol, 3,5-dimethoxy-4-hydroxybenzene, homovanillic acid, ferulic acid, 3-ethoxy-4-hydroxybenzaldehyde and guaiacol, all of which are compounds with strong or moderate activity and four compounds with weak vir-inducing activity. In view of the specificity of vir-inducers, our data extended observations of others and enabled us to define the specific structural features of a vir-inducer molecule. In addition we show here that induction of the octopine Ti vir-genes is (i) optimal at 29° C and totally abolished at 37° C., and (ii) strongly inhibited at low concentrations of sodium chloride. The implications for plant transformation are discussed.
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  • 49
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: IS481v1 and IS481v2 are two copies of a Bordetella pertussis insertion sequence element. We have shown that IS481V1 is located within 3kbp of the start of the adenylate cyclase gene whilst IS481v2 is immediately adjacent to the end of the agglutinogen 2 gene and provides the stop codon for that gene. In addition, IS481v1 and IS481v2 were present at these two specific sites in nine strains of B. pertussis, including two Phase IV strains which expressed neither adenylate cyclase nor agglutinogen 2 and three Phase I strains which did not express agglutinogen 2. The loss of expression in these strains is not the result of DNA rearrangements at the sites of IS481 v1 or IS481v2.
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  • 50
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The dicB operon of Escherichia coli, which was previously shown to code for a small protein inhibiting cell division, expresses a second inhibitor, DicF. Inhibition by DicF requires the transcription of a short (at the most 65 nucleotides long) stretch of DNA, acts in trans, and does not require the expression of other components of the dicABCF locus. The characteristics of the DNA sequence strongly suggest that division inhibition does not involve the translation of dicF mRNA into protein.
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  • 51
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In Aspergillus nidulans, the gene prnB encoding the major proline transport system is one of a cluster of four genes necessary and sufficient for the utilization of proline as sole nitrogen and/or carbon source. The prn cluster has been cloned and the sequence and transcript map of the prnB gene are presented in this paper. The predicted translated sequence consists of 570 amino acids, resulting in a molecular weight of 63028 Daltons. Its hydropathy profile shows 10 hydrophobic segments typical of integral membrane proteins. No N-terminal hydrophobic signal peptide is present, the N-terminal and C-terminal ends of the protein being hydrophilic. Similar results were previously found for the arginine and histidine transporters of Saccharomyces cerevisiae, with which the prnB transporter shares regions of highly conserved amino acid sequences. Using S1 mapping and Northern blot analyses, we confirm the presence of a unique inducible prnB transcript of 1.9 kb.
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  • 52
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The transcriptional pattern of the 22 min region of the Escherichia coli chromosome containing the linked sulA and ompA genes, which encode an SOS-inducible inhibitor of cell division and a constitutively expressed, major outer membrane protein, respectively, has been re-examined. During normal growth, the sulA gene was repressed whereas the ompA gene produced a stable 1250 nucleotide transcript. Counter-transcription of sulA occurred from a promoter situated in the sulA-ompA intergenic region and the product of this transcriptional circuit, named isf, is a 353 nucleotide untranslated RNA. Since the isf RNA is complementary to the 3-end of the sulA transcript, it could modulate sulA function by serving as an anti-messenger.On induction of the SOS-response, massive transcription of sulA took place, resulting in the ‘silencing’ of the isf gene, production of an abundant ∼615 nucleotide sulA mRNA and a novel hybrid transcript of ∼2100 nucleotides encoding both the SulA and OmpA proteins. Production of the latter RNA species, caused by transcription reading through the sulA terminator, the intergenic region and the coding sequences, was accompanied by a decrease in the abundance of the ompA mRNA as a result of promoter occlusion. However, the amount of OmpA protein produced was only slightly reduced.
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  • 53
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Hybrid 5′ regulatory regions were constructed in which the upstream activator sequence (UAS) and promoter of various nif genes were exchanged with the upstream regulatory sequence (URS) of the fdhF gene from Escherichia coli. They were analysed for their regulatory response under different growth conditions with the aid of fdhF′-′lacZ or nif′-′lacZ fusions. Placement of the UAS from the Bradyrhizobium japonicum nifH gene in front of the spacer (DNA region between URS and promoter) plus promoter from fdhF renders fdhF expression activatable by the Klebsiella pneumoniae NIFA protein, both under aerobic and anaerobic conditions. This excludes the possibility that the spacer of the fdhF 5’flanking region contains a site recognized by a putative oxygen- or nitrate-responsive repressor. There was also considerable activation by NIFA of fdhF expression in a construct lacking the nifH UAS but containing the fdhF spacer plus promoter. Further experimental evidence suggests that this reflects a direct interaction between NIFA and RNA polymerase at the nfrA-dependent promoter. A second set of hybrid constructs in which the URS from fdhF (E. coli) was placed In front of the nifD spacer plus promoter from B. Japonicum or in front of the K. pneumoniae nifH, nifU, nifB spacers and promoters, delivered inactive constructs in the case of the nifD, nifU and nifB genes. However, a nifH′-′lacZ fusion preceded by its own spacer and promoter plus the foreign fdhF URS displayed all the regulatory characteristics of fdhF expression, i.e. anaerobic induction with formate and repression by oxygen and nitrate. Although it is not known why only one out of the four nif promoters could be activated by the fdhF URS, this result nevertheless demonstrates that the various regulatory stimuli affecting expression of fdhF in E. coli have their target at the upstream regulatory sequence.
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  • 54
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Clinical isolates of Neisseria gonorrhoeae are commonly subject to growth inhibition by phenylpyruvate or by L-phenylalanine. A blockade of tyrosine biosynthesis is indicated since inhibition is reversed by either L-tyrosine or 4-hydroxyphenylpyruvate. Phenylalanine-resistant (PheR) and phenylalanine-sensitive (Phes) isolates both have a single 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase that is partially inhibited by L-phenylalanine (80%). However, PheS and PheR isolates differ in that the ratio of phenylpyruvate aminotransferase to 4-hydroxyphenylpyruvate aminotransferase is distinctly greater in PheS isolates than in PheR isolates. A mechanism for growth inhibition is proposed in which phenylalanine exerts two interactive effects, (i) Phenylalanine decreases precursor flow to 4-hydroxyphenylpyruvate through its controlling effect upon DAHP synthase; and (ii) phenylalanine is largely transaminated to phenylpyruvate, which saturates both aminotransferases, preventing transamination of an already limited supply of 4-hydroxyphenylpyruvate to L-tyrosine.
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  • 55
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The haemolytic activity of Serratia marcescens is determined by two proteins, ShIA and ShIB. ShIA integrates into the erythrocyte membrane and causes osmotic lysis through channel formation. The conformation of ShIA and its interaction with erythrocyte membranes were studied by determining the cleavage of ShIA by added trypsin. Our results suggest that the conformation of inactive ShIA (from an ShIB− strain) differs from the active ShIA, and that in a hydrophobic environment (detergent or membrane) active ShIA assumes a conformation distinct from that in buffer. Only active haemolysin adsorbed to erythrocytes. ShIA was firmly integrated into the erythrocyte membrane since it was only released under conditions which also dissolved the integral erythrocyte membrane proteins. Moreover, ShIA integrated into ‘ghosts’ remained there and was not haemolytic when incubated with erythrocytes. From the trypsin cleavage pattern obtained with haemolysin and C-terminally truncated, but still active, haemolysin derivatives integrated into erythrocytes, and sealed and unsealed erythrocyte ‘ghosts’, we conclude that ShiA is preferentially cleaved by trypsin at a few sites but only from the inside of the erythrocyte. Haemolysin in the erythrocyte membrane forms a water-filled channel and is resistant to trypsin and other proteases.
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  • 56
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The quaternary structure of regulatory proteins undoubtedly plays an important role in the initiation of transcription and DNA replication. To date, the best-characterized regulatory proteins are oligomers in which protomers are bound together by isologous interactions. From the examples presented in this article, it appears that the formation of certain nucleoprotein complexes implicated in transcription initiation might involve heterologous rather than isologous interactions, allowing differentiation between two classes of transcription activators.
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  • 57
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A 71 kiloDalton antigen from Mycobacterium tuberculosis is recognized by antibodies and by T lymphocytes during infection (Britton et al., 1986a). Partial sequence analysis indicates a relationship between this antigen and the highly conserved family of 70-kiloDalton heat shock proteins (hsp70) (Young et al., 1988). Biochemical and serological characterization of the protein confirms its membership of the hsp70 gene family, and metabolic labelling demonstrates that it is a major component of the mycobacterial response to heat stress. The role of stress proteins as antigens during infection is discussed.
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  • 58
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The class 1 protein is a major protein of the outer membrane of Neisseria meningitidis, and an important immunodeterminant in humans. The complete nucleotide sequence for the structural gene of a class 1 protein has been determined. The sequence predicts a protein of 374 amino acids, preceded by a typical signal peptide of 19 residues. The hydropathy profile of the predicted protein sequence resembles that of the Escherichia coli and gonococcal porins. The predicted protein sequence of the class 1 protein exhibits considerable structural similarity to the gonococcal porins PIA and PIB. Western blot studies also reveal immunologically conserved domains between the class 1 protein, PIA and PIB. A restriction fragment from the class 1 gene hybridizes to gonococcal genomic fragments in Southern blots. In addition to the class 1 gene coding region there is a large open reading frame on the opposite strand.
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  • 59
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Bradyrhizobfum japonicum fixX gene was identified and shown to be essential for symbiotic and free-living, microaerobic nitrogen fixation. The fixX gene encodes a ferredoxin-like protein which may be Involved in a redox process (electron transport?) essential for nitrogenase activity. This gene was localized downstream of fixC and its expression was dependent on the fixB promoter, providing evidence for the existence of a fixBCX operon. Mutagenesis and sequence analysis of the unusually long, 709 bp leader region between the fixB promoter and the fixB structural gene did not reveal the presence of a nif or fix gene that was absolutely essential for nitrogen fixation. However, a short open reading frame (ORF) within this region encoding a polypeptide of 35 amino acids (ORF35) was shown to be efficiently translated. Chromosomal deletion of a 400bp DNA fragment covering ORF35 resulted in a three-fold reduction of the fixSCX mRNA level, which in turn also reduced the nitrogen fixation activity of this mutant. This suggests a possible post-transcriptional control mechanism for the expression of the fixBCX operon involving the stabilization of fixBCX mRNA by ribosomes actively translating ORF35.
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  • 60
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Trimethoprim resistance mediated by the Staphylococcus aureus multi-resistance plasmid pSK1 is encoded by a structure with characteristics of a composite transposon which we have designated Tn4003. Nucleotide sequence analysis of Tn4003 revealed it to be 4717 bp in length and to contain three copies of the insertion element IS257 (789-790 bp), the outside two of which are flanked by directly repeated 8-bp target sequences. IS257 has imperfect terminal inverted repeats of 27-28 bp and encodes for a putative transposase with two potential α-helix-turn-α-helix DNA recognition motifs. IS257 shares sequence similarities with members of the IS15 family of insertion sequences from Gram-negative bacteria and with ISS 1 from Streptococcus lactis. The central region of the transposon contains the dfrA gene that specifies the S1 dihydrofolate reductase (DHFR) responsible for trimethoprim resistance. The S1 enzyme shows sequence homology with type I and V trimethoprim-resistant DHFRs from Gram-negative bacteria and with chromosomally encoded DHFRs from Gram-positive and Gram-negative bacteria. 5’to dfrA is a thymidylate synthetase gene, designated thyE.
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  • 61
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    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Bacteria can respond to a variety of environmental stimuli by means of systems generally composed of two proteins. The first protein (sensor or transmitter) is usually a transmembrane protein with cytoplasmic and extracytoplasmic domains. The extracytoplasmic domain (sensor) senses the environment and transfers the signal through the transmembrane domain to the cytoplasmic domain (transmitter), which has kinase activity. The second protein is located in the cytoplasm and contains an amino-terminal domain (receiver), which can be phosphorylated by the transmitter, and a carboxy-terminal region (regulator), which regulates gene expression by binding to DNA. The transmitter and receiver modules (the kinase and its target) are conserved in all signal-transducing systems and are the‘core structure’of this two-component system. The sensors and the regulators vary according to the stimuli they respond to and the DNA structure they interact with. On the basis of their sequence homology, the proteins belonging to such two-component systems can be classified into different families, which are summarized in this review.
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  • 62
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The mini-circle is a transposable element which is present in Streptomyces coelicolor A3(2) in both free circular and chromosomally integrated linear forms. The nucleotide sequences of the mini-circle and its preferred site of integration in the Streptomyces lividans TK64 chromosome were determined. Three putative open reading frames were identified in the mini-circle sequence. The mini-circle does not appear to cause a target site duplication on transposition and does not have perfect terminal inverted repeats. The observed site-specificity of the mini-circle is not mediated by extensive homology between the element and the chromosomal integration site. Transposition of the mini-circle into the S. lividans chromosome was demonstrated and found to be some two orders of magnitude less efficient than integration of the circular form of the element, suggesting that the circular form of the mini-circle might be a normal intermediate in the transposition process.
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  • 63
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Morphological evidence has previously indicated that the periplasmic space of Escherichia coli is compartmentalized at sites corresponding to future sites of cell division. The borders of these morphological compartments are formed by localized zones of adhesion (periseptal annuli). In the present study, the technique of fluorescence recovery after photo-bleaching was used to determine whether these structures act as barriers to the free movement of proteins within the periplasm. The recovery of fluorescence in the ftsA filaments was found to be uniformly low over at potential sites of cell division and at the cell poles, indicating that these regions are biochemically sequestered from the remainder of the periplasmic space. Our results provide direct evidence for local compartments within the periplasm, primarily located at the sites of past or future cell divisions. The implications of this finding for cell division and other periplasmic processes are discussed.
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  • 64
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A plasmid vector, pYZ1, was constructed which lacks most of the β-lactamase signal-peptide coding region, but has a unique EcoRI site spanning codons 2 and 3 of the resultant cytoplasmic β-lactamase derivative. Short quasi-random DNA sequences were cloned into the EcoRI site and Escherichia coli transformants in which some translocation of β-lactamase across the cytoplasmic membrane was restored were selected by their ability to survive and form colonies on plates containing a low level of ampicillin. About 15–20% of all in-frame inserts restored some β-lactamase trans-location and the salient feature of these sequences was their marked hydrophobicity. These results are discussed in the light of a similar study in which sequences able to function as translocators of invertase in yeast were cloned and analysed (Kaiser et al., 1987).
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  • 65
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The complete Escherichia coli ftsQ coding sequence, together with part of the ftsA coding sequence, has been cloned upstream of the lacZ open reading frame in a λ-vector (λJFL100). Cells which are lysogenic for λJFL100 transcribe the cloned lacZ from promoter(s) within the ftsQ and ftsA sequences. The level of β-galactosidase produced is dependent on growth rate (and/or cell size) and Is derepressed in an ftsA-deficient mutant. Transcription during the cell cycle is restricted to the time of cell division.
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  • 66
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Development of penicillin resistance in Streptococcus pneumoniae is due to successive mutations in penicillin-binding proteins (PBPs) which reduce their affinity for β-lactam antibiotics. PBP2x is one of the high-Mr PBPs which appears to be altered both in resistant clinical isolates, and in cefotaxime-resistant laboratory mutants. In this study, we have sequenced a 2564 base-pair chromosomal fragment from the penicillin-sensitive S. pneumoniae strain R6, which contains the PBP2x gene. Within this fragment, a 2250 base-pair open reading frame was found which coded for a protein having an Mr of 82.35 kD, a value which is in good agreement with the Mr of 80–85kD measured by SDS-gel electrophoresis of the PBP2x protein itself. The N-terminal region resembled an unprocessed signal peptide and was followed by a hydrophobic sequence that may be responsible for membrane attachment of PBP2x. The corresponding nucleotide sequence of the PBP2x gene from C504, a cefotaxime-resistant laboratory mutant obtained after five selection steps, contained three nucleotide substitutions, causing three amino acid alterations within the β-lactam binding domain of the PBP2x protein. Alterations affecting similar regions of Escherichia coli PBP3 and Neisseria gonorrhoeae PBP2 from β-lactam-resistant strains are known. The penicillin-binding domain of PBP2x shows highest homology with these two PBPs and S. pneumoniae PBP2b. In contrast, the N-terminal extension of PBP2x has the highest homology with E. coli PBP2 and methicillin-resistant Staphylococcus aureus PBP2′. No significant homology was detected with PBP1a or PBP1b of Escherichia coli, or with the low-Mr PBPs.
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  • 67
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In Kiebsiella pneumoniae, the mucoid phenotype, which is a virulence factor, is distinct from capsule production. It is positively controlled by a plasmid gene, designated rmpA. When introduced into certain Escherichia coli strains, rmpA induces expression of a mucoid phenotype, which results from overproduction of colanic acid at 30° C but not at 37°C. In E. coli, production of colanic acid is regulated by three genes: rcsA and rcsB which act as positive regulators, and rcsC which is a negative effector. In this work we present evidence that the rmpA gene complemented an rcsA, Ion double mutant of E. coli, but not an rcsA, ion+ isolate. This leads to the suggestion that rmpA expressed an rcsA-like activity and like rcsA, was negatively controlled at post-transcriptional level by the Lon protease. The nucleotide sequence of rmpA is reported. No homology could be found between the 27 kiloDalton RcsA protein and the deduced amino acid sequence of the 15.5 kiloDalton RmpA protein. Another gene, rmpB, which was required in E. coli recA isolates for full expression of rmpA at 30° C, has been identified on the K. pneumoniae virulence plasmid and shown to encode a 37 kiloDalton protein. Although rmpB was closely linked to rmpA, it was not present on the same transcriptional unit. These results suggested that induction of colanic acid synthesis by the K. pneumoniae virulence gene rmpA, was, at least in E. coli, under the control of the RecA network via rmpB, which may act as a positive regulator of rmpA. We conclude that these plasmid genes may function in K. pneumoniae as regulatory genes controlling the mucoid phenotype, which is itself encoded by the chromosome.
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  • 68
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Transcriptional regulation of the deoP2 promoter by the cyclic AMP/cyclic AMP receptor protein complex (cAMP/CRP) and the CytR repressor requires two high-affinity CRP targets located around -41 and -93 bp preceding the start site for transcription. Here we report the structure of cddP, another CRP/CytR-regulated promoter. In common with what was found in deo, the cdd promoter also contains multiple CRP targets. Thus, using the DNasel footprinting procedure, tandem CRP binding sites were identified around -41 and -93. These findings support a general model for CytR binding and CytR regulation, in which (i) CytR and the CRP/cAMP complex bind to similar or Identical targets, (ii) two or more targets are necessary for proper binding of CytR to a promoter region, and (iii) CytR represses transcription by antagonizing cAMP/CRP activation.
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  • 69
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The HI (now renamed fliC; lino et al., 1988) alleles specifying antigenically different Salmonella flagellins are identical at their ends but differ greatly towards the middle, where there are two hypervariable segments (regions IV and VI). The flagellar antigen, d, of Salmonella typhi, is found also as phase-1 antigen in many other Saimonella species. We cloned the H1-d gene of a strain of S. typhi and determined the nucleotide sequence of its two hypervariable regions. Comparison with gene H1-d of Salmonella muenchen showed substantial differences in region VI: four scattered amino acid differences and ten adjacent amino acids in the inferred S. typhi sequence, all of which differ from the corresponding nine amino acids in the S. muenchen sequence. The results of polymerase chain reaction amplification indicated the presence of the S. typhi version in all of 18 additional S. typhi strains and the presence of the S. muenchen version in all four non-S. typhi species with flagellar antigen d. The difference in amino acid sequence in segment VI may be responsible for the minor serological differences between antigens d of S. typhi and antigen d of S. muenchen.
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  • 70