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JOURNAL OF BACTERIOLOGY, Mar. 1987, p. 1127-1136 Vol. 169, No. 3 0021-9193/87/031127-10$02.00/0
 

Summary: JOURNAL OF BACTERIOLOGY, Mar. 1987, p. 1127-1136 Vol. 169, No. 3
0021-9193/87/031127-10$02.00/0
Copyright 1987, American Society for Microbiology
Genetic and Structural Analysis of the Rhizobium melilotifixA, fixB,
fixC, and fixX Genes
CHRISTOPHER D. EARL,"2t CLIVE W. RONSON,"3t AND FREDERICK M. AUSUBEL1*
Department of Genetics, Harvard Medical School, and Department ofMolecular Biology, Massachusetts General
Hospital, Boston, Massachusetts 021141; Department of Cellular and Developmental Biology, Harvard University,
Cambridge, Massachusetts 021382; and Grasslands Division, Department ofScientific and Industrial Research, Private
Bag, Palmerston North, New Zealand3
Received 18 August 1986/Accepted 25 November 1986
The fixA, fixB, fixC, and flxX genes of Rhizobium meliloti 1021 constitute an operon and are required for
nitrogen fixation in alfalfa nodules. DNA homologous to the R. melilotifixABC genes is present in all other
Rhizobium and Bradyrhizobium species examined, butJlxABC-homologous sequences were found in only one
free-living diazotroph, Azotobacter vinelandii. To determine whether the fixABCX genes share sequence
homology with any of the 17 KlebsieUla pneumoniae nifgenes, we determined the entire nucleotide sequence of
the fixA, fixB, fixC, and fixX genes and defined four open reading frames that code for polypeptides of
molecular weights 31,146, 37,786, 47,288, and 10,937, respectively. Neither DNA nor amino acid sequence
homology to the R. melilotifixA, -B, -C, and -X genes was found in the K. pneumoniae nifoperon. The fixX gene
contains a cluster of cysteine residues characteristic of ferredoxins and is highly homologous to an Azotobacter

  

Source: Ausubel, Frederick M. - Department of Genetics, Harvard University

 

Collections: Biology and Medicine