RESUMO
The Azospirillum brasilense trpE gene has been isolated by DNA hybridization and by genetic complementation of an Escherichia coli trpE deletion mutant. DNA sequence analysis of a 3.1-kb PstI restriction fragment of A. brasilense revealed the presence of an open reading frame encoding a putative TrpE(G) fusion protein. Previously an A. brasilense clone containing trpGDC was identified (Zimmer et al. Mol Gen Genet 229:41-51, 1991). It can, therefore, be concluded that A. brasilense contains two trpG genes. A putative leader peptide is found upstream of trpE(G), containing three consecutive tryptophan residues. Putative terminator and anti-terminator loops have also been identified. The LLESX10S motif, which is responsible for feedback inhibition by tryptophan in other TrpE proteins, is absent in the A. brasilense TrpE(G) fused protein.
Assuntos
Antranilato Sintase/genética , Azospirillum brasilense/genética , Genes Bacterianos/genética , Transferases de Grupos Nitrogenados , Sequência de Aminoácidos , Clonagem Molecular , Dosagem de Genes , Dados de Sequência Molecular , Conformação de Ácido Nucleico , Óperon/genética , Sinais Direcionadores de Proteínas/genética , RNA Bacteriano/química , RNA Mensageiro/química , Sequências Reguladoras de Ácido Nucleico/genética , Mapeamento por Restrição , Análise de Sequência de DNA , Homologia de Sequência de Aminoácidos , Transferases/genéticaRESUMO
Plant growth promotion by rhizobacteria is a widely spread phenomenon. However only a few rhizobacteria have been studied thoroughly. Rhizobium is the best-studied rhizobacterium. It forms a symbiosis with a restricted host range. Azospirillum is another plant-growth-promoting rhizobacterium which forms rhizocoenoses with a wide range of plants. In both bacteria, the interaction with the plant involves the attraction toward the host plant and the attachment to the surface of the root. Both bacteria are attracted to plant roots, but differ in specificity. Attachment to plant roots occurs in two steps for both bacteria: a quick, reversible adsorption, and a slow, irreversible anchoring to the plant root surface. However, for the two systems under study, the bacterial surface molecules involved in plant root attachment are not necessarily the same.
RESUMO
The nucleotide sequence of the Azospirillum brasilense exoB gene, located on plasmid pRhico, has been determined. The A. brasilense ExoB protein shows significant homology with other prokaryotic UDP-glucose 4'-epimerases (EC 5.1.3.2).
Assuntos
Azospirillum brasilense/genética , Genes Bacterianos , Análise de Sequência de DNA , UDPglucose 4-Epimerase/genética , Sequência de Aminoácidos , Azospirillum brasilense/enzimologia , Dados de Sequência Molecular , Homologia de Sequência de Aminoácidos , UDPglucose 4-Epimerase/químicaRESUMO
Two Azospirillum brasilense loci that correct Rhizobium meliloti exoB and exoC mutants for exopolysaccharide (EPS) synthesis have been identified previously (K. W. Michiels, J. Vanderleyden, A. P. Van Gool, E. R. Signer, J. Bacteriol., 1988b). A. brasilense exo mutants produce EPS of lower molecular weight than the wild type strain. Here, we show by hybridization that these exo loci are located on a 90-MDa plasmid in A. brasilense Sp7. In four other Azospirillum strains but not in A. lipoferum SpBr17, the loci are likewise located on a plasmid of approximately the same size. Transposon Tn5 insertions in these loci were isolated and mapped on the cloned DNA by restriction analysis. Hybridization of restriction digests of purified 90-MDa plasmid DNA with probes containing the exo loci confirmed their plasmid location. This is the first report on plasmid localization of genes in Azospirillum.