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Gene Review

proX  -  glycine betaine/proline ABC transporter...

Escherichia coli str. K-12 substr. MG1655

Synonyms: ECK2673, JW2654, osrA, proU
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Disease relevance of proX


High impact information on proX

  • The proU locus encodes an osmotically inducible glycine betaine transport system that is important in the adaptation to osmotic stress [4].
  • Osmoregulated expression of proU has been reconstituted in a cell-free system. proU encodes an osmotically inducible, high-affinity transport system for the osmoprotectant glycine betaine in Escherichia coli [5].
  • Previously, a proU-lacZ fusion gene had been cloned, resulting in plasmid pOS3 [5].
  • In vivo osmoregulation of this extrachromosomal proU-lacZ fusion gene at low copy number showed that the plasmid-encoded fusion contained all the necessary sequences in cis for correctly receiving osmoregulatory signals during induction by osmotic stress and repression by glycine betaine [5].
  • The ionic compound potassium glutamate specifically stimulated proU-lacZ expression in a concentration-dependent manner [5].

Chemical compound and disease context of proX


Biological context of proX

  • The proU locus is organized in an operon and the position of the structural gene (proV) for GBBP is defined using a minicell system [1].
  • We cloned this locus into both low-copy-number lambda vectors and multicopy plasmids and demonstrated that these clones restore osmotically controlled synthesis of the periplasmic glycine betaine binding protein (GBBP) and the transport of glycine betaine in a delta (proU) strain [1].
  • Two full-length transporters could complement the Na(+)-sensitive phenotype of the Escherichia coli mutant deficient in betT, putPA, proP, and proU [8].
  • The nucleotide sequence of 1.5-kilobase-pair fragment that contains the transcriptional control region of the proU operon and the coding sequences specifying 290 amino acids of the first structural gene of the operon was determined [2].

Associations of proX with chemical compounds

  • The protein was absent in mutants with lambda placMu insertions in the proU region, a locus involved in transport of the osmoprotectant glycine betaine [9].
  • The purified protein binds glycine betaine with high affinity but has no affinity for either proline or choline, clarifying the role of proU in osmoprotectant transport [9].
  • Potassium acetate also induced some proU expression, but other salts were ineffective, thereby ruling out ionic strength as the stimulatory signal [5].
  • High concentrations of sucrose, trehalose, or glycine betaine did not induce proU expression in vitro either, eliminating osmolarity per se as the stimulus [5].
  • Osmosensitivity in the gltBD strains, elicited either by lysine supplementation or by introduction of the argP or glnE mutations (but not proU mutations), was also correlated with a reduction in cytoplasmic glutamate pools in cultures grown at elevated osmolarity [10].

Analytical, diagnostic and therapeutic context of proX

  • DNA sequences similar to the putP, proP, and proU loci of E. coli K-12 were detected by DNA amplification and (or) hybridization and protein specifically reactive with antibodies raised against the ProX protein of E. coli K-12 (a ProU constituent) was detected by western blotting in over 95% of the isolates [7].


  1. Cloned structural genes for the osmotically regulated binding-protein-dependent glycine betaine transport system (ProU) of Escherichia coli K-12. Faatz, E., Middendorf, A., Bremer, E. Mol. Microbiol. (1988) [Pubmed]
  2. Nucleotide sequence of the transcriptional control region of the osmotically regulated proU operon of Salmonella typhimurium and identification of the 5' endpoint of the proU mRNA. Overdier, D.G., Olson, E.R., Erickson, B.D., Ederer, M.M., Csonka, L.N. J. Bacteriol. (1989) [Pubmed]
  3. Construction and characterization of a proU-gfp transcriptional fusion that measures water availability in a microbial habitat. Axtell, C.A., Beattie, G.A. Appl. Environ. Microbiol. (2002) [Pubmed]
  4. A physiological role for DNA supercoiling in the osmotic regulation of gene expression in S. typhimurium and E. coli. Higgins, C.F., Dorman, C.J., Stirling, D.A., Waddell, L., Booth, I.R., May, G., Bremer, E. Cell (1988) [Pubmed]
  5. In vitro reconstitution of osmoregulated expression of proU of Escherichia coli. Ramirez, R.M., Prince, W.S., Bremer, E., Villarejo, M. Proc. Natl. Acad. Sci. U.S.A. (1989) [Pubmed]
  6. Adaptation of Escherichia coli to high osmolarity environments: osmoregulation of the high-affinity glycine betaine transport system proU. Lucht, J.M., Bremer, E. FEMS Microbiol. Rev. (1994) [Pubmed]
  7. Genes encoding osmoregulatory proline/glycine betaine transporters and the proline catabolic system are present and expressed in diverse clinical Escherichia coli isolates. Culham, D.E., Emmerson, K.S., Lasby, B., Mamelak, D., Steer, B.A., Gyles, C.L., Villarejo, M., Wood, J.M. Can. J. Microbiol. (1994) [Pubmed]
  8. Functional characterization of betaine/proline transporters in betaine-accumulating mangrove. Waditee, R., Hibino, T., Tanaka, Y., Nakamura, T., Incharoensakdi, A., Hayakawa, S., Suzuki, S., Futsuhara, Y., Kawamitsu, Y., Takabe, T., Takabe, T. J. Biol. Chem. (2002) [Pubmed]
  9. Purification and characterization of a glycine betaine binding protein from Escherichia coli. Barron, A., Jung, J.U., Villarejo, M. J. Biol. Chem. (1987) [Pubmed]
  10. Osmosensitivity associated with insertions in argP (iciA) or glnE in glutamate synthase-deficient mutants of Escherichia coli. Nandineni, M.R., Laishram, R.S., Gowrishankar, J. J. Bacteriol. (2004) [Pubmed]
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