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Vol. 169, No. 4JOURNAL OF BACTERIOLOGY, Apr. 1987, p. 1423-1432 0021-9193/87/041423-10$02.00/0
 

Summary: Vol. 169, No. 4JOURNAL OF BACTERIOLOGY, Apr. 1987, p. 1423-1432
0021-9193/87/041423-10$02.00/0
Copyright 1987, American Society for Microbiology
Identification and Characterization of the Rhizobium meliloti ntrC
Gene: R. meliloti Has Separate Regulatory Pathways for Activation
of Nitrogen Fixation Genes in Free-Living and Symbiotic Cells
WYNNE W. SZETO,1t B. TRACY NIXON,1t CLIVE W. RONSON,1'2t AND FREDERICK M. AUSUBELL*
Department ofGenetics, Harvard Medical School, and Department ofMolecular Biology, Massachusetts General
Hospital, Boston, Massachusetts 02114,1 and Grasslands Division, Department of Scientific and Industrial Research,
Palmerston North, New Zealand2
Received 23 June 1986/Accepted 16 December 1986
We show here that Rhizobium meliloti, the nitrogen-fixing endosymbiont of alfalfa (Medicago sativa), has a
regulatory gene that is structurally homologous to previously characterized ntrC genes in enteric bacteria. DNA
sequence analysis showed thatR. meliloti ntrC is homologous to previously sequenced ntrC genes from Klebsiella
pneumoniae and Bradyrhizobium sp. (Parasponia) and that an ntrB-like gene is situated directly upstream from
R. meliloti ntrC. Similar to its counterparts in K. pneumoniae and Escherichia coli, R. meliloti ntrC is expressed
when the cells are grown in nitrogen-limiting media. In addition, R. meliloti ntrC is required for growth on
media containing nitrate as the sole nitrogen source and for the ex planta transcription of several R. meliloti nif
genes. On the other hand, root nodules elicited by R. melioti ntrC mutants fix nitrogen as well as nodules
elicited by wild-type R. meliloti. These latter results indicate that R. meliloti has separate regulatory pathways

  

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

 

Collections: Biology and Medicine