Structural and functional analysis of the fixLJ genes of Rhizobium leguminosarum biovar phaseoli CNPAF512 |
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Authors: | Inge D''hooghe Jan Michiels Katrien Vlassak Christel Verreth Francisca Waelkens Jos Vanderleyden |
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Affiliation: | (1) F. A. Janssens Laboratory of Genetics, Catholic University of Leuven, W. de Croylaan 42, B-3001 Heverlee, Belgium |
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Abstract: | The fixLJ genes of Rhizobium leguminosarum biovar phaseoli CNPAF512 were identified by DNA hybridization of a genomic library with an internal fragment of the Rhizobium meliloti fixJ gene. The nucleotide sequence was determined and the corresponding amino acid sequence was aligned with the amino acid sequences of the FixL proteins of R. meliloti, Bradyrhizobium japonicum and Azorhizobium caulinodans. While the FixJ protein and the carboxy-terminal part of the FixL protein are highly homologous to the other FixL and FixJ proteins, the homology in the central heme-binding, oxygen-sensing domain and in the amino-terminal domain of FixL is very low. The R. leguminosarum bv. phaseoli FixL protein does not contain the heme-binding motif defined for the previously described FixL proteins. R. leguminosarum bv. phaseoli fixLJ and fixJ mutants were constructed. These mutants can still fix nitrogen, albeit at a reduced level. Expression analysis of nifA-gusA and nifH-gusA fusions in the constructed mutants revealed that the R. leguminosarum bv. phaseoli fixLJ genes are involved in microaerobic nifH expression but not in nifA expression.The nucleotide sequence data reported will appear in the EMBL, Genbank and DDBJ Nucleotide Sequence Databases under the accession number U27314 |
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Keywords: | Rhizobium leguminosarum biovar phaseoli fixLJ genes Two-component systems Nitrogen fixation Gene regulation |
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