Disease relevance of proX

• The proU locus of Escherichia coli encodes a high-affinity, binding-protein-dependent transport system (ProU) for the osmoprotectant glycine betaine [1].
• Southern blot analysis of 15 proU transposon insertions in Salmonella typhimurium indicated that this operon is at least 3 kilobase pairs in length [2].
• This fusion between the proU promoter from Escherichia coli and the reporter gene gfp was introduced into strains of E. coli, Pantoea agglomerans, and Pseudomonas syringae [3].

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

• Adaptation of Escherichia coli to high osmolarity environments: osmoregulation of the high-affinity glycine betaine transport system proU [6].
• All tests were calibrated with E. coli K-12 derivatives from which genetic loci putP (encoding a proline transporter required for proline catabolism), proP, and (or) proU (loci encoding osmoregulatory proline/glycine betaine transporters) had been deleted [7].

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].

References