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- Title
Rhizobium leguminosarum bv. viciae contains a second fnr/fixK-like gene and an unusual fixL homologue.
- Authors
Patschowski, Thomas; Schlüter, Andreas; Priefer, Ursula B.
- Abstract
Genes of <em>Rhizobium leguminosarum</em> bv. <em>viciae</em> VF39 coding for the regulatory elements NifA, FixL and FixK were isolated, sequenced and genetically analysed. The <em>fixK-fixL</em> region is located upstream of the <em>fixNOQP</em> operon on the non-nodulation plasmid pRleVF39c. The deduced amino acid sequence of FixL revealed an unusual structure in that it contains a receiver module (homologous to the N-terminal domain of response regulators) fused to its transmitter domain. An oxygen-sensing haem-binding domain, found in other FixL proteins, is conserved in <em>R. leguminosarum</em> bv. <em>viciae</em> FixL. <em>R. leguminosarum</em> bv. <em>viciae</em> possesses a second <em>fnr-like</em> gene, designated <em>fixK</em>, whose encoded gene product is very similar to <em>Rhizobium meliloti</em> and <em>Azorhizobium caulinodans</em> FixK. Individual <em>R. leguminosarum</em> bv. <em>viciae fixK</em> and <em>fixL</em> inserti on mutants displayed a Fix+ phenotype. A reduced nitrogen-fixation activity was found for a <em>R. leguminosarum</em> bv. <em>viciae fnrV-deletion</em> mutant, whereas no nitrogen-fixation activity was detectabie for a <em>fixKlfnrN</em> double mutant. The <em>R. leguminosarum</em> bv. <em>viciae nifA</em> gene is expressed independently of FixL and FixK under aerobic and microaerobic conditions, whereas <em>fixL</em> gene expression is induced under microaerobiosis. Another <em>orf</em> was identified downstream of <em>fixK-fixL</em> and encodes a product which has homology to pseudoazurins from different species. Mutation of this azu gene showed that it is dispensable for nitrogen fixation.
- Publication
Molecular Microbiology, 1996, Vol 21, Issue 2, p267
- ISSN
0950-382X
- Publication type
Academic Journal
- DOI
10.1046/j.1365-2958.1996.6321348.x