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  • 1
    Electronic Resource
    Electronic Resource
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 31 (1999), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A haem peroxidase different from other microbial, plant and animal peroxidases is described. The enzyme is secreted as two isoforms by dikaryotic Pleurotus eryngii in peptone-containing liquid medium. The corresponding gene, which presents 15 introns and encodes a 361-amino-acid protein with a 30-amino-acid signal peptide, was isolated as two alleles corresponding to the two isoforms. The alleles differ in three amino acid residues and in a seven nucleotide deletion affecting a single metal response element in the promoter. When compared with Phanerochaete chrysosporium peroxidases, the new enzyme appears closer to lignin peroxidase (LiP) than to Mn-dependent peroxidase (MnP) isoenzymes (58–60% and 55% identity respectively). The molecular model built using crystal structures of three fungal peroxidases as templates, also showed high structural affinity with LiP (Cα-distance 1.2 Å). However, this peroxidase includes a Mn2+ binding site formed by three acidic residues (E36, E40 and D175) near the haem internal propionate, which accounts for the ability to oxidize Mn2+. Its capability to oxidize aromatic substrates could involve interactions with aromatic residues at the edge of the haem channel. Another possibility is long-range electron transfer, e.g. from W164, which occupies the same position of LiP W171 recently reported as involved in the catalytic cycle of LiP.
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  • 2
    Electronic Resource
    Electronic Resource
    Osney Mead, Oxford OX2 0EL, UK : Blackwell Science Ltd
    Molecular microbiology 18 (1995), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: STB secretion-deficient mutants were isolated using the synthetic transposon TnβIaM. Cultures were plated using a double-membrane system of cellulose acetate and nitrocellulose placed on Luria agar plates containing carbenicillin. The STB bound to the underlying nitrocellulose membrane was detected with anti-STB antibodies. The altered genes of two STB secretion-deficient mutants were identified by conjugation and complementation as toIC and dsbA. In cultures of well-characterized dsbA and toIC mutants, STB was absent from the culture supernatant. The role of ToIC and DsbA in the secretion of peptides is discussed.
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  • 3
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A region of 7.8 kb of the plasmid pMB2 from Enterococcus faecalis S-48 carrying the information necessary for production and immunity of the peptide antibiotic AS-48 has been cloned and sequenced. It contains the as-48A structural gene plus five open reading frames (as-48B, as-48C, as-48C1, as-48D and as-48D1 ). Besides As-48D, all the predicted gene products are basic hydrophobic proteins with potential membrane-spanning domains (MSDs). None of them shows any homology with protein sequences stored in databanks, except for As-48D, which shows similarity to the C-terminal domain of ABC transporters and contains a highly conserved ATP-binding site. The gene products of as-48B, as-48C, as-48C1 and as-48D are thought to be involved in AS-48 production and secretion. The only gene able to provide resistance to AS-48 by itself is as-48D1. Immunity also seems to be enhanced at least by the products of as-48B, as-48C1 and as-48D genes. Transcription analysis using probes derived from the different ORFs revealed two large (3.5 and 2.7 kb) mRNAs, suggesting that the different genes are organized in two constitutive operons.
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  • 4
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: By sequence analysis of Sinorhizobium meliloti strain GR4 plasmid pRmeGR4b, we have identified a group II intron named RmInt1 inserted within the insertion sequence ISRm2011-2 of the IS630-Tc1/IS3 retroposon superfamily. Like some other group II introns, RmInt1 possesses, in addition to the structurally conserved ribozyme core, an open reading frame (ORF) with homology to reverse transcriptases. Using a T7 expression system in Escherichia coli, we show that the intron is active in splicing in vivo and that splicing efficiency requires the intron-encoded ORF, which suggests that the putative intron encoded protein has a maturase function. DNA hybridization studies indicate that intron RmInt1 is widespread within S. meliloti native populations and appears to be mostly located within this IS element. Nevertheless, some S. meliloti strains harbour one copy of RmInt1 at a different location. DNA sequence analysis of the 5′ exon of one of these heterologous intron insertion sites revealed the presence of a putative IS element closely related to insertion sequence ISRm2011-2. The intron-binding sites (IBS1 and IBS2 motifs) are conserved, although a transition of a G→A in the IBS1 has occurred. Our results demonstrate an association of intron RmInt1 with particular insertion sequences of the IS630-Tc1/IS3 retroposon superfamily that may have ensured the spread and maintenance of this group II intron in S. meliloti.
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  • 5
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Pseudomonas aeruginosa is a prolific exporter of virulence factors and contains three of the four protein secretion systems that have been described in Gram-negative bacteria. The P. aeruginosa type II general secretory pathway (GSP) is used to export the largest number of proteins from this organism, including lipase, phospholipase C, alkaline phosphatase, exotoxin A, elastase and LasA. Although these exoproteins contain no sequence similarity, they are specifically and efficiently transported by the secretion apparatus. Bacterial homologues of XcpQ (GspD), the only outer membrane component of this system, have been proposed to play the role of gatekeeper, by presumably interacting and recognizing the exported substrates to allow their passage through the outer membrane. While determining the phenotype of non-polar deletions in each of the xcp genes, we have shown that a deletion of the P. aeruginosa strain K xcpQ does not completely abolish protein secretion. As the proposed function of XcpQ should be requisite for secretion, we searched for additional factors that could carry out this role. A cosmid DNA library from a PAK strain deleted for xcpP-Z was tested for its ability to increase protein secretion by screening for enhanced growth on lipid agar, a medium that selects for the secretion of lipase. In this manner, we have identified an XcpQ homologue, XqhA, that is solely responsible for the residual export observed in a ΔxcpQ strain, although it is not required for efficient secretion in wild-type P. aeruginosa. We have also demonstrated that this protein is capable of recognizing all of the exoproteins of P. aeruginosa, arguing against the proposed role of members of the secretin family as determinants of specificity.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Aquaculture research 30 (1999), S. 0 
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The effects of 21 weeds acting as hosts of tomato spotted wilt virus (TSWV), temperature, thrips population and diversity on disease progress in chrysanthemum cv. Polaris were studied. Under greenhouse conditions, only Taraxacum officinale, Bidens sp., Resedaluteola and Mirabilis jalapa were hosts for TSWV. Of 38 weeds species in the area surrounding a chrysanthemum field, Tithonia tubaeformis and R. luteola had the highest populations of adult and immature thrips. These weeds, as well as M. jalapa, had an extensive seasonal distribution and may play a key role in the disease progress. Seventeen thrips species belonging to the genera Bravothrips, Thrips and Frankliniella were identified on weed flowers, with Frankliniella occidentalis (FOC) representing 9.5% of all thrips identified. Of 123 thrips collected from chrysanthemum inflorescences, 9.75% were FOC, and only 2.5% of them transmitted TSWV. Of all the thrips species collected from chrysanthemum flowers in the field, only FOC was capable of transmitting TSWV. On 120 experimental plots established at two sites, with three transplanting dates (June, July and August), it was estimated that 1.25% of the chrysanthemum cuttings were already infected with TSWV when transplanted. Secondary spread, vectored by FOC, occurred only for the earliest transplanting date and resulted in a further 2.36% disease incidence.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Aquaculture nutrition 3 (1997), S. 0 
    ISSN: 1365-2095
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The total fat content and the fatty acids of total lipids (TL), phospholipids (PL) and triacylglycerols (TAG) were analysed in white muscle from wild and reared red porgy, Pagrus pagrus (L.). The fat percentage was higher in reared (3.03 ± 0.57%) (mean ± SE) than wild (0.65 ± 0.03%) fish. The fatty acid pattern of reared porgy TL reflected the diet's lipid. Wild red porgy showed higher levels of ω3 and ω6 polyunsaturated fatty acids (PUFA) than reared, but both the atherogenic index and the index of thrombogenicity were very low for both wild and reared red porgy. The lipid fractions showed that the PL were composed of very high levels of PUFA, especially 22:6ω3, and their composition seemed to be better regulated than the composition of TAG. TAG showed greater differences between wild and reared fish, presumably because they reflected the dietary content of lipids. PUFA were the principal component of wild red porgy TAG.
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  • 9
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: K/T boundary geochemical anomalies have been used previously to support the impact event at the end of the Cretaceous. However, impact models and assessment of the extraterrestrial contribution to the boundary sediments should also consider the diagenetic alteration of the impact signatures. Mineralogical and geochemical studies centring on redox proxies reveal differences in trace-element concentrations at Agost and Caravaca (SE Spain), two of the most complete K/T boundary sections. These differences probably derive from variations in the diagenetic evolution of the ejecta layer. Several redox proxies, such as extensive pyrite formation, high authigenic uranium concentration and positive Eu anomalies, indicate very strong reducing conditions at Agost. Positive Eu anomalies are extremely unusual in sediments, and in this case are interpreted to indicate a highly reducing environment. In such conditions, certain trace elements such as Ir, may have been remobilized, thereby masking the original signature of the impact.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 19 (1996), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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