Identification and sequence of a nifJ-like gene in Rhodospirillum rubrum: partial characterization of a mutant unaffected in nitrogen fixation

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Identification and sequence of a nifJ-like gene in Rhodospirillum rubrum : partial characterization of a mutant unaffected in nitrogen fixation

A nifJ-like gene was identified in the photosynthetic purple non-sulphur bacterium Rhodospirillum rubrum. A DNA segment hybridizing to Klebsiella pneumoniae nifJ was isolated, the gene was inactivated, and a mutant strain, SNJ-1, was constructed by allele replacement. The mutation was confirmed by DNA sequencing. Northern blotting and by the lack of pyruvate oxidoreductase activity. This is the first report of a nifJ-like gene in photosynthetic bacteria. Unexpectedly, SNJ-1 was capable of nitrogen fixation, and growth was similar to the wild-type strain under all conditions investigated. Therefore, this is also the first demonstration that a nifJ homologue, when present, is not essential for nitrogen fixation in a diazotroph. The nifJ-like gene was sequenced and found to have considerable similarity to published nifJ gene sequences from other organisms. By primer extension, the initiation site for transcription was located, and a typical sigma 54 promoter sequence was identified.

By the author/editor: Lindblad, A; Jansson, J; Brostedt, E; Johansson, Magnu ...; Hellman, U; Nordlund, S

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NATURAL SCIENCES: NATURAL SCIENCES; and Biological Scien ...; and Biochemistry and ...

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