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  • 1
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Transposon mutagenesis was used to locate the genes for phaseolotoxin biosynthesis inPseudomonas syringae pathovar.phaseolicola. Mutants unable to produce toxin were obtained that carried Tn5 on different chromosomal restriction fragments. None of the Tn5-induced nontoxigenic mutants carried the transposon in plasmid DNA. The insertion of Tn5 intotox DNA was confirmed by site-directed mutagenesis. The results reported here suggest the involvement of at least five chromosomal genes in phaseolotoxin biosynthesis. All of the toxinminus mutants retained both full pathogenicity on beans and resistance to the toxin.
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  • 2
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. A β-mannanase gene (manA) was isolated from the extremely thermophilic bacterium Dictyoglomus thermophilum Rt46B.1. ManA is a single-domain enzyme related to one group of β-mannanases (glycosyl hydrolase family 26). The manA gene was expressed in the heat-inducible vector pJLA602 and the expression product, ManA, purified to homogeneity. The recombinant ManA is a monomeric enzyme with a molecular mass of 40 kDa and an optimal temperature and pH for activity of 80°C and 5.0. In the absence of substrate, the enzyme showed no loss of activity at 80°C over 16 h, while at 90°C the enzyme had a half-life of 5.4 min. Hydrolysis of the galactomannan locust bean gum (LBG) by purified ManA released mainly mannose, mannobiose, and mannotriose, confirming that ManA is an endo-acting β-mannanase. Sequence comparisons with related β-mannanases has allowed the design of consensus PCR primers for the identification and isolation of related genes.
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  • 3
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The genome of the anaerobic thermophilic eubacteriumCaldocellum saccharolyticum was analyzed by pulsed field gel electrophoresis. The restriction endonucleasesNheI andSstII cleaved the genome into 23 and 21 fragments, respectively, and the sums of the fragments gave a genome size of approximately 2.78 Mbp. Hybridization of probes for several cellulolytic and hemicellulolytic genes, as well as a 16S ribosomal RNA gene, gave complex signals on PFGE-separated restriction fragments. Mapping of the genome by use of linking clone hybridizations had been initiated.
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  • 4
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. DNA sequencing techniques have revealed widespread molecular diversity of the genomic organization of apparently closely related bacteria (as judged from SSU rDNA sequence similarity). We have previously described the extreme thermophile Caldicellulosiruptor saccharolyticus, which is unusual in possessing multi-catalytic, multidomain arrangements for the majority of its glycosyl hydrolases. We report here the sequencing of three gene clusters of glycosyl hydrolases from Caldicellulosiruptor sp. strain Tok7B.1. These clusters are not closely linked, and each is different in its organization from any described for Cs. saccharolyticus. The catalytic domains of the enzymes belong to glycosyl hydrolase families 5, 9, 10, 43, 44, and 48. The cellulose binding domains (CBDs) of these enzymes from Caldicellulosiruptor sp. Tok7B.1 are types IIIb, IIIc, or VI. A number of individual catalytic and binding domains have been expressed in Escherichia coli, and biochemical data are reported on the purified enzymes for cellulose degradation encoded by engineered derivatives of celB and celE.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 150 (1977), S. 161-170 
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In order to perform complementation tests with mutations of DNA replication of F′-plasmids incompatibility must be overcome. We report our inability to duplicate the results presented by Palchoudhury and Iyer (1971) and Bezanson and Iyer (1975) who have claimed to demonstrate the autonomous replication of two incompatible F′-plasmids in a strain carrying the temperature sensitivednaB43 allele. In addition, we describe experiments designed to measure complementation using transient heterozygote and compatible plasmids. Assessment of our data and those of others in the light of a recent report by Uhlin and Nordström (1975) suggests that new approaches will have to be developed for the successful employment of complementation analysis in F-plasmid genetics.
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  • 6
    ISSN: 1617-4623
    Keywords: Thermus ; Leucine operon ; Complementation ; Promoter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The organisation of the leucine genes in Thermus thermophilus HB8 was analysed by examining the ability of recombinant DNAs to complement Escherichia coli mutations. The arrangement of the genes is different from that in the mesophilic bacteria E. coli and Salmonella typhimurium. The promoter responsible for the expression of the leuB, leuC and leuD genes of Thermus HB8 in E. coli was identified. The sequence of Thermus DNA containing this promoter revealed structural similarities to the promoter and attenuator regions of the E. coli leucine operon.
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  • 7
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Microorganisms employ a large array of enzymes to break down the cellulose and hemicelluloses of plant biomass. These enzymes, especially those with high thermal stability, have many uses in biotechnology. We have solved the crystal structure of a β-1,4-xylanase, XynB, from the extremely thermophilic bacterium Dictyoglomus thermophilum, isolate Rt46B.1. The protein crystallized from 1.6 M ammonium sulfate, 0.2 M HEPES pH 7.2 and 10% glycerol, with unit-cell parameters a = b = 91.3, c = 44.9 Å and space group P43. The structure was solved at high resolution (1.8 Å) by X-ray crystallography, using the method of isomorphous replacement with a single mercury derivative, and refined to a final R factor of 18.3% (Rfree = 22.1%). XynB has the single-domain fold typical of family 11 xylanases, comprising a jelly roll of two highly twisted β-sheets that create a deep substrate-binding cleft. The two catalytic residues, Glu90 and Glu180, occupy this cleft. Compared with other family 11 xylanases, XynB has a greater proportion of polar surface and has a slightly extended C-terminus that, combined with the extension of β-strand A5, gives additional hydrogen bonding and hydrophobic packing. These factors may account for the enhanced thermal stability of the enzyme.
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  • 8
    ISSN: 1433-4909
    Keywords: Key words Heterologous expression ; Thermostable xylanase ; Protein secretion ; Plasmid stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The yeast Kluyveromyces lactis has been developed as a host for extracellular production of thermophilic hemicellulases by employing expression vectors based on the 2μ-like plasmid pKD1 of Kluyveromyces drosophilarium. A β-1,4-xylanase gene (xynA) from the extreme thermophile Thermotoga sp. strain FjSS3B.1 was fused in-frame with a synthetic secretion signal derived from the K. lactis killer toxin and expressed under control of the K. lactis LAC4 (β-galactosidase) promoter. Correctly processed xylanase enzyme with full biological activity on oat spelts xylan was secreted during shake-flask cultivation of K. lactis transformants. The transcriptional activity of the LAC4 promoter dramatically affected mitotic stability of the expression vector under nonselective conditions. However, one combination of host strain and expression plasmid showed higher stability and good yield and has been employed for scaled-up production of XynA and other thermostable hemicellulases in chemostat culture. XynA secreted by K. lactis is as thermostable as the native enzyme, having a half-life of 48 h at 90°C.
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  • 9
    ISSN: 1433-4909
    Keywords: Key words Xylanases ; Genomic walking PCR ; Multidomain enzymes ; Cellulose-binding domains ; Linker sequences ; Horizontal gene transfer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Three family 10 xylanase genes (xynA, xynB, and xynC) and a single family 11 xylanase gene (xynD) were identified from the extreme thermophile Caldicellulosiruptor strain Rt69B.1 through the use of consensus PCR in conjunction with sequencing and polyacrylamide gel electrophoresis. These genes appear to comprise the complete endoxylanase system of Rt69B.1. The xynA gene was found to be homologous to the xynA gene of the closely related Caldicellulosiruptor strain Rt8B.4, and primers designed previously to amplify the Rt8B.4 xynA gene could amplify homologous full-length xynA gene fragments from Rt69B.1. The complete nucleotide sequences of the Rt69B.1 xynB, xynC, and xynD genes were obtained using genomic walking PCR. The full-length xynB and xynC genes are more than 5 kb in length and encode highly modular enzymes that are the largest xylanases reported to date. XynB has an architecture similar to the family 10 xylanases from Thermoanaerobacterium saccharolyticum (XynA) and Clostridium thermocellum (XynX) and may be cell wall associated, while XynC is a bifunctional enzyme with an architecture similar to the bifunctional β-glycanases from Caldicellulosiruptor saccharolyticus. The xynD gene encodes a two-domain family 11 xylanase that is identical in architecture to the XynB family 11 xylanase from the unrelated extreme thermophile Dictyoglomus thermophilum strain Rt46B.1. The sequence similarities between the Rt69B.1 xylanases with respect to their evolution are discussed.
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  • 10
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The xynC gene coding for an acetylxylan esterase from the extreme thermophile “Caldocellum saccharolyticum” was overexpressed in Escherichia coli strain RR28 by cloning the gene downstream from the lacZ promoter region of pUC18 (pNZ1447) or downstream from the temperature-inducible λp r p l promoters of pJLA602 (pNZ1600). The protein formed high molecular weight aggregates in induced cells of RR28/pNZ1600 but not in RR28/pNZ1447. The enzyme constituted up to 10% of the total cell protein and was located in the cytoplasmic fraction of RR28/pNZ1447. The acetyl esterase was most active at pH 6.0 and 70–75° C with a half-life of 64 h at 70° C and 30 h at 80° C, respectively.
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