A cosmid able to complement the Nif- and nitrate-dependent growth phenotypes of the Azospirillum brasilense mutant FP9 was isolated from a genomic library of the wild-type strain FP2. A 6-kb DNA region was sequenced and showed two open reading frames (ORFs) identified as the ntrB and ntrC genes. An ORF1 located upstream from the ntrB gene and coding for a 36-kDa polypeptide showed similarity to the nifR3 gene of Rhodobacter capsulatus and the ORF1 of Rhizobium leguminosarum, both located upstream from the ntrB gene in a complex operon. Two other unidentified ORFs (ORF5 and partial ORF4) coding for hydrophobic polypeptides were also observed. delta ORF1-ntrBC, ORF1, ntrB, and ntrC mutants obtained by recombination of suicide plasmids containing an insertion of a promoterless lacZ kanamycin cassette showed decreased nitrogenase activities and were unable to grow on nitrate as the sole N source. These phenotypes were restored by complementation with plasmids containing the ntrC gene. Analysis of lacZ transcriptional fusions suggested that the ORF1-ntrBC operon in Azospirillum brasilense is expressed from a promoter located upstream from the ORF1 and that it is negatively regulated by the ntrC gene product.
| Predicate | Object |
|---|---|
| rdf:type | |
| rdfs:comment |
A cosmid able to complement the Nif- and nitrate-dependent growth phenotypes of the Azospirillum brasilense mutant FP9 was isolated from a genomic library of the wild-type strain FP2. A 6-kb DNA region was sequenced and showed two open reading frames (ORFs) identified as the ntrB and ntrC genes. An ORF1 located upstream from the ntrB gene and coding for a 36-kDa polypeptide showed similarity to the nifR3 gene of Rhodobacter capsulatus and the ORF1 of Rhizobium leguminosarum, both located upstream from the ntrB gene in a complex operon. Two other unidentified ORFs (ORF5 and partial ORF4) coding for hydrophobic polypeptides were also observed. delta ORF1-ntrBC, ORF1, ntrB, and ntrC mutants obtained by recombination of suicide plasmids containing an insertion of a promoterless lacZ kanamycin cassette showed decreased nitrogenase activities and were unable to grow on nitrate as the sole N source. These phenotypes were restored by complementation with plasmids containing the ntrC gene. Analysis of lacZ transcriptional fusions suggested that the ORF1-ntrBC operon in Azospirillum brasilense is expressed from a promoter located upstream from the ORF1 and that it is negatively regulated by the ntrC gene product.
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| skos:exactMatch | |
| uniprot:name |
Can. J. Microbiol.
|
| uniprot:author |
Funayama S.,
Machado H.B.,
Pedrosa F.O.,
Rigo L.U.,
Souza E.M.,
Steffens M.B.R.,
Yates M.G.
|
| uniprot:date |
1995
|
| uniprot:pages |
674-684
|
| uniprot:title |
The ntrBC genes of Azospirillum brasilense are part of a nifR3-like-ntrB-ntrC operon and are negatively regulated.
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| uniprot:volume |
41
|