Identification, cloning, and sequence analysis of the nitrogen regulation gene ntrC of Agrobacterium tumefaciens C58

We describe the cloning of an ntrC gene of Agrobacterium tumefaciens C58 by interspecific complementation of an Escherichia coli ntrC mutant. Restriction mapping and Southern blot analysis of the complementing clone identified a 1.7-kb EcoRI-PvuII DNA fragment whose sequence was determined. Analysis of this sequence revealed coding regions corresponding to a complete ntrC gene and the C-terminal region of an ntrB gene. Amino acid sequence comparisons of A. tumefaciens NTRC protein with NTRC sequences from Rhizobium meliloti, Bradyrhizobium sp. (Parasponia), Klebsiella pneumoniae, E. coli, and Salmonella typhimurium show strong sequence conservation supporting DNA hybridization data, demonstrating strong evolutionary homology among ntrC genes of Rhizobiaceae. The C58 NTRC protein has been identified, by 35S-labeling, in a T7 RNA polymerase (pT7-7) expression vector system.