Document Detail

Identification and characterization of two nitrogen fixation regulatory regions, nifA and nfrX, in Azotobacter vinelandii and Azotobacter chroococcum.
MedLine Citation:
PMID:  3294559     Owner:  NLM     Status:  MEDLINE    
Five Tn5-induced Nif- mutants of Azotobacter vinelandii were characterized as regulatory mutants because they were restored to Nif+ by the introduction of constitutively expressed nifA from Klebsiella pneumoniae. The mutants fell into two different classes on the basis of hybridization to a Rhizobium leguminosarum nifA gene probe and by complementation with cosmids isolated from pLAFRI gene banks of A. vinelandii and Azotobacter chroococcum. One mutant, MV3, was located in or near a nifA gene. The others, MV12, MV16, MV18 and MV26, defined a new regulatory gene, which has been called nfrX. The lack of expression of different nif-lacZ fusions confirmed the regulatory phenotype of all five mutant strains. The ability of both nifA and nfrX mutants to grow on nitrogen-free medium with vanadium, but not on medium with molybdenum, suggests that neither gene is required for expression of the alternative V-containing nitrogenase of A. vinelandii. A fragment carrying Tn5 and flanking DNA from MV3 was used as a probe to isolate the nifA region of A. chroococcum. Ligation of two adjacent EcoRI fragments of A. chroococcum yielded an intact nifA gene that activated expression of nifH-lac fusions and also restored MV3 to Nif+. The four nfrX mutants were complemented by pLAFR1 cosmids pLV163 and pLC121. The nfrX gene was subcloned from pLV163 and located within a 3.2 kb fragment. To determine whether nfrX might be found in other nitrogen-fixing organisms, DNA from 13 different species was hybridized to an nfrX probe. The failure to observe hybridization suggests that nfrX may be specific to nif regulation in Azotobacter.
E Santero; A Toukdarian; R Humphrey; C Kennedy
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Molecular microbiology     Volume:  2     ISSN:  0950-382X     ISO Abbreviation:  Mol. Microbiol.     Publication Date:  1988 May 
Date Detail:
Created Date:  1988-08-29     Completed Date:  1988-08-29     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  8712028     Medline TA:  Mol Microbiol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  303-14     Citation Subset:  IM    
AFRC--Institute of Plant Science Research, University of Sussex, Brighton, UK.
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MeSH Terms
Azotobacter / genetics*
Bacterial Proteins / genetics
Chromosome Mapping
Cloning, Molecular
DNA, Recombinant
Gene Expression Regulation
Genes, Bacterial
Klebsiella pneumoniae / genetics
Nitrogen Fixation / genetics*
Nucleic Acid Hybridization
Rhizobium / genetics
Species Specificity
Reg. No./Substance:
0/Bacterial Proteins; 0/DNA, Recombinant

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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