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  • 1
    Electronic Resource
    Electronic Resource
    DNA sequence and genetic analysis of the Rhodobacter capsulatus nifENX gene region: Homology between NifX and NifB suggests involvement of NifX in processing of the iron-molybdenum cofactor (1989)
    Springer
    Molecular genetics and genomics 216 (1989), S. 353-363 
    Details
    ISSN: 1617-4623
    Keywords: Rhodobacter capsulatus ; Nitrogen fixation ; DNA sequence analysis ; nifE, nifN, nifX genes ; Protein comparisons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Rhodobacter capsulatus genes homologous to Klebsiella pneumoniae nifE, nifN and nifX were identified by DNA sequence analysis of a 4282 bp fragment of nif region A. Four open reading frames coding for a 51188 (NifE), a 49459 (NifN), a 17459 (NifX) and a 17472 (ORF4) dalton protein were detected. A typical NifA activated consensus promoter and two imperfect putative NifA binding sites were located in the 377 bp sequence in front of the nifE coding region. Comparison of the deduced amino acid sequences of R. capsulatus NifE and NifN revealed homologies not only to analogous gene products of other organisms but also to the α and β subunits of the nitrogenase iron-molybdenum protein. In addition, the R. capsulatus nifE and nifN proteins shared considerable homology with each other. The map position of nifX downstream of nifEN corresponded in R. capsulatus and K. pneumoniae and the deduced molecular weights of both proteins were nearly identical. Nevertheless, R. capsulatus NifX was more related to the C-terminal end of NifY from K. pneumoniae than to NifX. A small domain of approximately 33 amino acid residues showing the highest degree of homology between NifY and NifX was also present in all nifB proteins analyzed so far. This homology indicated an evolutionary relationship of nifX, nifY and nifB and also suggested that NifX and NifY might play a role in maturation and/or stability of the iron-molybdenum cofactor. The open reading rame (ORF4) downstream of nifX in R. capsulatus is also present in Azotobacter vinelandii but not in K. pneumoniae. Interposon-induced insertion and deletion mutants proved that nifE and nifN were necessary for nitrogen fixation in R. capsulatus. In contrast, no essential role could be demonstrated for nifX and ORF4 whereas at least one gene downstream of ORF4 appeared to be important for nitrogen fixation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00334376
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  • 2
    Electronic Resource
    Electronic Resource
    Nucleotide sequence and genetic analysis of the Rhodobacter capsulatus ORF6-nifU I SVW gene region: possible role of Nif W in homocitrate processing (1993)
    Springer
    Molecular genetics and genomics 238 (1993), S. 369-382 
    Details
    ISSN: 1617-4623
    Keywords: Nitrogen fixation ; Novel type of NifU ; Ethane formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract DNA sequence analysis of a 3494-bp HindIII-Bc1I fragment of the Rhodobacter capsulatus nif region A revealed genes that are homologous to ORF6, nifU, nifS, nifV and nifW from Azotobacter vinelandii and Klebsiella pneumoniae. R. capsulatus nifU, which is present in two copies, encodes a novel type of NifU protein. The deduced amino acid sequences of NifUI and NifUII share homology only with the C-terminal domain of NifU from A. vinelandii and K. pneurnoniae. In contrast to nifA andnifB which are almost perfectly duplicated, the predicted amino acid sequences of the two NifU proteins showed only 39% sequence identity. Expression of the ORF6-nifU ISVW operon, which is preceded by a putative σ54-dependent promoter, required the function of NifA and the nif-specific rpoN gene product encoded by nifR4. Analysis of defined insertion and deletion mutants demonstrated that only nifS was absolutely essential for nitrogen fixation in R. capsulatus. Strains carrying mutations in nifV were capable of very slow diazotrophic growth, whereas ORF6, nifU I and nifW mutants as well as a nifU I/nifUII, double mutant exhibited a Nif+ phenotype. Interestingly, R. capsulatus nifV mutants were able to reduce acetylene not only to ethylene but also to ethane under conditions preventing the expression of the alternative nitrogenase system. Homocitrate added to the growth medium repressed ethane formation and cured the NifV phenotype in R. capsulatus. Higher concentrations of homocitrate were necessary to complement the NifV phenotype of a polar nifV mutant (NifV−NifW−), indicating a possible role of NifW either in homocitrate transport or in the incorporation of this compound into the iron-molybdenum cofactor of nitrogenase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00291996
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  • 3
    Electronic Resource
    Electronic Resource
    Consequences of the iron-dependent formation of ferredoxin and flavodoxin on photosynthesis and nitrogen fixation on Anabaena strains (1990)
    Springer
    Photosynthesis research 26 (1990), S. 119-125 
    Details
    ISSN: 1573-5079
    Keywords: Anabaena ; ferredoxin ; flavodoxin ; FPLC determination of ferredoxin and flavodoxin ; Iron deficiency ; Nitrogen fixation ; Photosynthesis ; strain differences in gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Iron-dependent formation of ferredoxin and flavodoxin was determined in Anabaena ATCC 29413 and ATCC 29211 by a FPLC procedure. In the first species ferredoxin is replaced by flavodoxin at low iron levels in the vegetative cells only. In the heterocysts from Anabaena ATCC 29151, however, flavodoxin is constitutively formed regardless of the iron supply. Replacement of ferredoxin by flavodoxin had no effect on photosynthetic electron transport, whereas nitrogen fixation was decreased under low iron conditions. As ferredoxin and flavodoxin exhibited the same Km values as electron donors to nitrogenase, an iron-limited synthesis of active nitrogenase was assumed as the reason for inhibited nitrogen fixation. Anabaena ATCC 29211 generally lacks the potential to synthesize flavodoxin. Under iron-starvation conditions, ferredoxin synthesis is limited, with a negative effect on photosynthetic oxygen evolution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00047083
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