Molecular and General Genetics MGG

, Volume 212, Issue 1, pp 27–37 | Cite as

Genetic characterization and sequence analysis of the duplicated nifA/nifB gene region of Rhodobacter capsulatus

  • Bernd Masepohl
  • Werner Klipp
  • Alfred Pühler


A DNA region showing homology to Klebsiella pneumoniae nifA and nifB is duplicated in Rhodobacter capsulatus. The two copies of this region are called nifA/nifB copy I and nifA/nifB copy II. Deletion mutagenesis demonstrated that either of the two copies is sufficient for growth in nitrogen-free medium. In contrast, a double deletion mutant turned out to be deficient in nitrogen fixation. The complete nucleotide sequence of a 4838 bp fragment containing nifA/nifB copy I was determined. Two open reading frames coding for a 59653 (NifA) and a 49453 (NifB) dalton protein could be detected. Comparison of the amino acid sequences revealed that the R. capsulatus nifA and nifB gene products are more closely related to the NifA and NifB proteins of Rhizobium meliloti and Rhizobium leguminosarum than to those of K. pneumoniae. A rho-independent termination signal and a typical nif promoter region containing a putative NifA binding site and a consensus nif promoter are located within the region between the R. capsulatus nifA and nifB genes. The nifB sequence is followed by an open reading frame (ORF1) coding for a 27721 dalton protein in nifA/nifB copy I. DNA sequence analysis of nifA/nifB copy II showed that both copies differ in the DNA region downstream of nifB and in the noncoding sequence in front of nifA. All other regions compared, i.e. the 5′ part of nifA, the intergenic region and the 3′ part of nifB, are identical in both copies.

Key words

Rhodobacter capsulatus Nitrogen fixation nifA/nifB duplication Deletion analysis DNA sequence 


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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • Bernd Masepohl
    • 1
  • Werner Klipp
    • 1
  • Alfred Pühler
    • 1
  1. 1.Lehrstuhl für Genetik, Fakultät für BiologieUniversität BielefeldBielefeld 1Federal Republic of Germany

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