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  • 1
    Electronic Resource
    Electronic Resource
    Sequence and molecular analysis of the nifL gene of Azotobacter vinelandii (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 9 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In both Klebsiella pneumoniae and Azotobacter vinelandii the nifL gene, which encodes a negative regulator of nitrogen fixation, lies immediately upstream of nifA. We have sequenced the A. vinelandii nifL gene and found that it is more homologous in its C-terminal domain to the histidine protein kinases (HPKs) than Is K. pneumoniae NifL. In particular A. vinelandii NifL contains a conserved histidine at a position shown to be phosphorylated in other systems. Both NifL proteins are homologous in their N-termini to a part of the Halobacterium halobium bat gene product; Bat is involved in regulation of bacterio-opsin, the expression of which is oxygen sensitive. The same region showed homology to the haembinding N-terminai domain of the Rhizobium meliloti fixL gene product, an oxygen-sensing protein. Like K. pneumoniae NifL, A. vinelandii NifL is shown here to prevent expression of nif genes in the presence of NH+4 or oxygen. The sequences found homologous in the C-terminal regions of NifL, FixL and Bat might therefore be involved in oxygen binding or sensing. An in-frame deletion mutation in the nifL coding region resulted in loss of repression by NH+4 and the mutant excreted high amounts of ammonia during nitrogen fixation, thus confirming a phenotype reported earlier for an insertion mutation. In addition, nifLA are cotranscribed in A. vinelandii as in K. pneumoniae, but expression from the A. vinelandii promoter requires neither RpoN nor NtrC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01745.x
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  • 2
    Electronic Resource
    Electronic Resource
    Nitrogen fixation gene ( nifL ) involved in oxygen regulation of nitrogenase synthesis in K. peumoniae (1981)
    [s.l.] : Nature Publishing Group
    Nature 290 (1981), S. 424-426 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The nif-lac fusions constructed by Dixon et al.9 with phage Mud(Ap/ac), in which lac is expressed from nif promoters, could not be directly used for the isolation of regulatory mutants, as this phage can re-transpose to new locations at high frequency (about 10-4 per generation; R. Dixon, personal ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/290424a0
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  • 3
    Electronic Resource
    Electronic Resource
    IBP—nitrogen fixation (1976)
    [s.l.] : Nature Publishing Group
    Nature 261 (1976), S. 79-79 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] AN outstanding feature of the IBP synthesis meeting on nitrogen fixation held in Edinburgh in September 1973 was its international character. That very strength created a potential weakness as far as publication of the proceedings was concerned, and I remember sometimes labouring over abstracts at ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/261079a0
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  • 4
    Electronic Resource
    Electronic Resource
    Physiological characterisation of an Azotobacter vinelandii nifU-deletion mutant and its spontaneous Nif+ revertants that over-produce cytochrome bd (1999)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 175 (1999), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A nifU-deletion mutant of Azotobacter vinelandii fixed N2, but only under low atmospheric O2 (2 kPa), whereas, under air, it reverted to Nif+ at 5×10−8. The revertant's O2-tolerant nitrogenase activity, surprisingly, was not accompanied by an increased respiration rate, although, like cydR mutants, the revertants over-produce cytochrome bd. The introduction of a cydR mutation into the nifU mutant yielded transformants, of which 100% fixed N2 in air. This is consistent with the revertant mutations residing in cydR. Inactivation of CydR (a Fnr-like transcriptional repressor) could lead to the up-regulation of a process (e.g. IscU activity in iron-sulfur cluster formation) that substitutes for NifU.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1999.tb13618.x
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular analysis of the chromosomal region encoding the nifA and nifB genes of Acetobacter diazotrophicus (1999)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 176 (1999), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The Acetobacter diazotrophicus nifA gene was isolated by its ability to restore a Nif+ phenotype to a nifA mutant of Azotobacter vinelandii. Sequencing revealed that the nifA gene was upstream and adjacent to the nifB gene and both are transcribed in the same direction but independently from different promoters. The 3′ end of the nifB gene was located approximately 2.5 kb upstream of the nitrogenase structural gene cluster, nifHDK. The deduced amino acid sequences of the A. diazotrophicus nifA and nifB gene products were most similar to the NifA and NifB proteins of Azorhizobium caulinodans and Rhodobacter capsulatus, respectively. A. diazotrophicus nifA expression was repressed in cultures exposed to high levels of ammonium while oxygen apparently had no influence. Both oxygen and ammonium prevented expression of a nifB-reporter strain, consistent with the observation that ammonium repressed nifA expression, and indicating that A. diazotrophicus NifA activity is inhibited by oxygen as in other Proteobacterial α group diazotrophs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1999.tb13676.x
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  • 6
    Electronic Resource
    Electronic Resource
    Endophytic nitrogen fixation in dune grasses (Ammophila arenaria and Elymus mollis) from Oregon (2004)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 49 (2004), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Several tropical grasses harbor symbiotic nitrogen-fixing bacteria within their stem and rhizome tissue that may contribute to the nitrogen nutrition of the host plant. We present evidence here that sand dune grasses (Ammophila arenaria and Elymus mollis) from Oregon also contain nitrogen-fixing bacteria. Surface-sterilized stem and rhizome tissue from these species possess acetylene reduction (nitrogen fixation) activity and large populations (105 to 106 cfu/g fresh weight) of bacteria. These bacteria were cultured on N-free media and identified by sequencing of 16S rRNA genes or by GC-FAME. Random sequencing of numerous colonies from the initial isolation plates of mixed isolates showed that pseudomonads (Stenotrophomonas and Pseudomonas) were by far the most common microorganism. One isolate –Burkholderia sp. strain Aa1 – reduced acetylene in culture with maximum activity at an O2 concentration of 2% (v/v) in liquid media or 10% on solid media. PCR screening of all the isolates with nifH and nifD primers was positive only for this species. Immunolocalization studies with antibodies to nitrogenase resulted in labeling within plant cell walls of stems and rhizomes. Evidence for a similar nitrogen-fixing association was also detected in Uniola paniculata (sea oats) and Ammophila brevigulata (American beachgrass). We conclude that these grasses, and probably other dune grasses from temperate climates, contain endophytic, diazotrophic bacteria that may contribute to the phenomenal success of these grasses on nutrient-poor sand.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/j.femsec.2004.04.010
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  • 7
    Electronic Resource
    Electronic Resource
    Identification of sequences important for recognition of vnf genes by the VnfA transcriptional activator in Azotobacter vinelandii (1996)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 135 (1996), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract To analyze regulation of the vanadium-dependent nitrogenase of Azotobacter vinelandii, plasmids carrying vnfE-, vnfH-, or vnfD-lacZ fusions were transferred to Escherichia coli. These genes were expressed only if VnfA was present. Deletions of the vnfE upstream region were constructed and comparison of a region necessary for expression with sequences upstream of other vnf genes indicated a substantially conserved motif, GTAC-N6-GTAC, hypothesized to be the binding site for VnfA. This motif was duplicated with 17 or 18 bases lying between each in the vnfH and vnfD promoters. Deletion analysis of the vnfH promoter indicated that both motifs were necessary for full expression. In footprinting experiments, VnfA significantly protected from methylation the guanine residues within or immediately adjacent to the proposed VnfA recognition motifs. The active form of VnfA is probably interacting dimers, a tetramer, or a higher order oligomer since two regions of dyad symmetry are required for its interaction with the DNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1996.tb07992.x
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  • 8
    Electronic Resource
    Electronic Resource
    Activation of nif gene expression in Azotobacter by the nifA gene product of Klebsiella pneumoniae (1983)
    [s.l.] : Nature Publishing Group
    Nature 301 (1983), S. 626-628 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A wide host range multicopy plasmid carrying the nif A gene expressed from a constitutive promoter was constructed using pKT230 (rf. 22), a hybrid of RSF1010 (a Q incompatibility group plasmid) and pACYC177 (Fig. 1). A Sail fragment from pMCTIA21 carrying the nif A gene and flanking regions ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/301626a0
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  • 9
    Electronic Resource
    Electronic Resource
    The role of regulatory genes nifA, vnfA, anfA, nfrX, ntrC, and rpoN in expression of genes encoding the three nitrogenases of Azotobacter vinelandii (1994)
    Springer
    Archives of microbiology 162 (1994), S. 422-429 
    Details
    ISSN: 1432-072X
    Keywords: Nitrogen fixation ; Vanadium ; anf Azotobacter ; nif ; Sigma(σ)54 ; Sigma(σ)N ; Molybdenum ; vnf ; ntrC ; rpoN
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Several regulatory gene mutants of Azotobacter vinelandii were tested for ability to synthesize functional nitrogenase-1 (Nif phenotype), nitrogenase-2 (Vnf), or nitrogenase-3 (Anf). While nifA mutants were Nif-, Vnf+, and Anf+/-, and ntrC mutants were Nif+, Vnf+, and Anf+, nifA ntrC double mutants were Nif-, Vnf-, and Anf-. A vnfA mutant was Nif+, Vnf+/-, and Anf+/-, and an anfA strain was Nif+, Vnf+, and Anf-. lacZ fusions in the nifH, vnfH, vnfD, anfH, and nifM genes of Azotobacter vinelandii were constructed and introduced into wild-type and regulatory mutants of A. vinelandii. Expression of these operons correlated with the growth phenotype of the regulatory mutants. Apparently either NifA or NtrC can activate expression of nifM. Also, expression of the anf operon required the NifA transcriptional activator, although there are no NifA binding sites at appropriate locations upstream of anfH (or anfA). The results confirm previous reports that VnfA and AnfA are required for expression of vnf and anf genes, respectively, and that VnfA is involved in repression of the nifHDK operon in the absence of molybdenum and of the anfHDGK operon in the presence of vanadium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00282107
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  • 10
    Electronic Resource
    Electronic Resource
    Repressor properties of the nifL gene product in Klebsiella pneumoniae (1982)
    Springer
    Molecular genetics and genomics 185 (1982), S. 75-81 
    Details
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Certain mutations in the nifL gene of the Klebsiella pneumoniae nitrogen fixation (nif) gene cluster resulted in altered nif regulaiton such that nitrogenase synthesis was no longer repressed by low levels of exogenous fixed nitrogen, by oxygen or by high temperature. Introduction of a plasmid with a nifL + allele restored fixed nitrogen and oxygen repression. We therefore conclude that the nifL product acts as a nif-specific repressor in response to these effectors. Hence nif-specific regulation is controlled by the products of two regulatory genes, nifLA, which comprise a single operon. As previously reported (Dixon et al. 1980; Buchanan-Wollaston et al. 1981), the nifA product is necessary for transcription from other nif promoters but not from that of its own operon. We find that the nifL gene product also acts at other nif promoters but does not repress its own synthesis. Transcription of nifLA is in turn controlled by a general nitrogen-regulatory system in the cell, mediated by the products of the ntrA (glnF), ntrB (glnL) and ntrC (glnG) genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333793
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