An Fnr-like protein encoded in Rhizobium leguminosarum biovar viciae shows structural and functional homology to Rhizobium meliloti FixK |
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Authors: | Sergio Colonna-Romano Walter Arnold Andreas Schlüter Pierre Boistard Alfred Pühler Ursula B. Priefer |
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Affiliation: | (1) Faculty of Biology, Department of Genetics, University of Bielefeld, PO Box 8640, D-4800 Bielefeld 1, Germany;(2) Laboratoire de Biologie Moleculaire des Relations Plantes-Microorganismes, CNRS-INRA, BP27, F-31326 Castanet-Tolosan, France;(3) Present address: A.I.D. spa Zona Industriale Contrada S. Orsala, Cap 95030 Catania, Italy |
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Abstract: | Summary A 1.9 kb DNA region of Rhizobium leguminosarum biovar viciae strain VF39 capable of promoting microaerobic and symbiotic induction of the Rhizobium meliloti fixN gene was identified by heterologous complementation. Sequence analysis of this DNA region revealed the presence of two complete open reading frames, orf240 and orf114. The deduced amino acid sequence of orf240 showed significant homology to Escherichia coli Fnr and R. meliloti FixK. The major difference between ORF240 and FixK is the presence of 21 N-terminal amino acids in ORF240 that have no counterpart in FixK. A similar protein domain is also present in E. coli Fnr and is essential for the oxygen-regulated activity of this protein. Analysis of the nucleotide sequence upstream of orf240 revealed a motif similar to the NtrA-dependent promoter consensus sequence, as well as two DNA regions resembling the Fnr consensus binding sequence. A Tn5-generated mutant in orf240 lost the ability to induce the R. meliloti fixN-lacZ fusion. Interestingly, this mutant was still capable of nitrogen fixation but showed reduced nitrogenase activity. |
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Keywords: | Symbiotic nitrogen fixation Oxygen regulation Interspecies complementation Sequence analysis Anaeroboxes |
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