Nitrogenase reductase: A functional multigene family in Rhizobium phaseoli

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Abstract
The complete coding sequence of the nitrogenase reductase gene (nifH) is present in 3 different regions of a R. phaseoli symbiotic plasmid. Homology between 2 of the regions containing nifH coding sequences extends over 5 kilobases. These in turn share 1.3 kilobases of homology with the 3rd region. The nucleotide sequences of the 3 nitrogenase reductase genes were found to be identical. Site-directed insertion mutagenesis indicated that none of the 3 genes is indispensable for N2 fixation during symbiosis with Phaseolus vulgaris. Evidently, at least 2 of the reiterated genes can be functionally expressed.