title: Two-component regulatory systems responsive to environmental stimuli share strongly conserved domains with the nitrogen assimilation regulatory genes ntrB and ntrC.
abstract: We report that the ntrB and ntrC proteins of Bradyrhizobium sp. [Parasponia] strain RP501 share homology with other regulatory proteins. There is extensive conservation of C-terminal regions between products of RP501 ntrB; Klebsiella pneumoniae ntrB; Escherichia coli envZ, cpxA, and phoR; Agrobacterium tumefaciens virA; and, to a lesser extent, E. coli cheA. There is also extensive conservation of N-terminal regions between products of RP501 ntrC; K. pneumoniae ntrC; E. coli ompR, sfrA, phoB, cheY and cheB; Salmonella typhimurium cheB and cheY; Bacillus subtilis spoOA and spoOF; and A. tumefaciens virG. We propose that these regulatory genes comprise two-component regulatory systems that evolved from a common ancestral system that involved transduction of information about the status of the environment by one protein domain (the C-terminal regions conserved among ntrB, envZ, etc.) to a second one (the N-terminal region conserved among ntrC, ompR, etc.). The ntrC-set protein then acts upon a specific responding mechanism, typically as a transcriptional activator but also as an effector of the maturation of outer membrane proteins or as a modulator of the direction of flagella rotation.
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000032:analysis; D002633:Chemotaxis; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000032:analysis; D005798:Genes, Bacterial; D005809:Genes, Regulator; D009584:Nitrogen / Q000378:metabolism*; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D009584:Nitrogen