Mutational analysis reveals functional similarity between NARX, a nitrate sensor in Escherichia coli K-12, and the methyl-accepting chemotaxis proteins.
During anaerobic growth, nitrate induces synthesis of the anaerobic respiratory enzymes formate dehydrogenase-N and nitrate reductase. This induction is mediated by a transcription activator, the narL gene product. The narX gene product may be involved in sensing nitrate and phosphorylating NARL. We isolated narX mutants, designated narX*, that caused nitrate-independent expression of the formate dehydrogenase-N and nitrate reductase structural genes. We used lambda narX specialized transducing phage to genetically analyze these lesions in single copy. Two previously isolated narX* mutations, narX32 and narX71, were also constructed by site-specific mutagenesis. We found that each of these alleles caused nitrate-independent synthesis of formate dehydrogenase-N and nitrate reductase, and each was recessive to narX+. The narX* mutations lie in a region of similarity with the methyl-accepting chemotaxis protein Tsr. We suggest that the narX* proteins have lost a transmembrane signalling function such that phosphoprotein phosphatase activity is reduced relative to protein kinase activity.
Collins
L A
LA
Section of Genetics, Cornell University, Ithaca, New York 14853-8101.
Egan
S M
SM
Stewart
V
V
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000235:genetics*; D005816:Genetic Complementation Test; D008565:Membrane Proteins / Q000235:genetics*; D000072236:Methyl-Accepting Chemotaxis Proteins; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000494:pharmacology; D016296:Mutagenesis; D009154:Mutation / Q000235:genetics; D009566:Nitrates / Q000494:pharmacology*; D010641:Phenotype; D011494:Protein Kinases; D016415:Sequence Alignment / Q000379:methods; D012689:Sequence Homology, Nucleic Acid; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; D009566:Nitrates; C057635:Tsr protein, Bacteria; C000607604:tsr protein, E coli; C044659:molybdate; D008982:Molybdenum; D011494:Protein Kinases; C074787:narX protein, E coli