Topology of the PhoR protein of Escherichia coli and functional analysis of internal deletion mutants

Mol Microbiol. 1993 Apr;8(2):269-75. doi: 10.1111/j.1365-2958.1993.tb01571.x.


The PhoR protein of Escherichia coli K-12 belongs to a family of structurally related sensor-kinases that regulate responses to environmental stimuli. These proteins are often located in the inner membrane with two membrane-spanning segments that are separated by a periplasmic domain, which is supposed to sense the environmental stimuli. However, the hydrophobicity plot of PhoR suggests a somewhat different topology in which a large periplasmic domain is lacking and an extended cytoplasmic domain is present besides the kinase domain. In protease-accessibility experiments and by using phoR-phoA gene fusions, the topology of PhoR was investigated and the absence of a large periplasmic domain was confirmed. Furthermore, the function of the extended cytoplasmic domain was studied by creating internal deletions. The mutations in this domain resulted in a constitutive expression of the pho regulon, indicating that the mutant PhoR proteins are locked in their kinase function. We propose that this extended cytoplasmic domain functions by sensing an internal signal that represses the kinase function of the PhoR protein.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Escherichia coli / enzymology*
  • Escherichia coli / genetics
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Operon
  • Phosphoprotein Phosphatases / chemistry*
  • Phosphoprotein Phosphatases / genetics
  • Phosphorylation
  • Protein Conformation*
  • Protein Kinases / chemistry*
  • Protein Kinases / genetics
  • Protein Processing, Post-Translational
  • Recombinant Fusion Proteins / metabolism
  • Sequence Deletion
  • Signal Transduction*
  • Trans-Activators / genetics


  • Bacterial Proteins
  • Membrane Proteins
  • Recombinant Fusion Proteins
  • Trans-Activators
  • PhoR protein, Bacteria
  • Protein Kinases
  • Phosphoprotein Phosphatases