EnvZ-OmpR Interaction and Osmoregulation in Escherichia coli

Abstract

EnvZ, a histidine kinase/phosphatase inEscherichia coli, responds to the osmolarity changes in the medium by regulating the phosphorylation state of the transcription factor OmpR, which controls the expression levels of outer membrane porin proteins OmpF and OmpC. Although both ompRand envZ genes are located on the ompB locus under the control of the ompB promoter and transcribed as a single polycistronic mRNA, the expression of envZ is known to be significantly less than ompR. However, to date no accurate estimation for the amounts of EnvZ and OmpR in the cell has been carried out. Here we examined the levels of EnvZ and OmpR in the wild-type strain MC4100 by quantitative Western blot analysis using anti-OmpR and anti-EnvZc (cytoplasmic domain of EnvZ) antisera. It was observed that during exponential growth in L-broth medium there were ∼3500 and 100 molecules per cell of OmpR and EnvZ, respectively. The levels of OmpR and EnvZ in MC4100 cells grown in a high osmolarity medium (nutrient broth with 20% sucrose) were about the same as those grown in L-broth, whereas they were 1.7-fold higher than those in a low osmolarity medium (nutrient broth). With His10-OmpR, we also determined that theK d value for the EnvZc-OmpR complex formation is 1.20 ± 0.17 μm. On the basis of these results, the molecular mechanism of osmoregulation of ompF andompC is discussed. EnvZ, a histidine kinase/phosphatase inEscherichia coli, responds to the osmolarity changes in the medium by regulating the phosphorylation state of the transcription factor OmpR, which controls the expression levels of outer membrane porin proteins OmpF and OmpC. Although both ompRand envZ genes are located on the ompB locus under the control of the ompB promoter and transcribed as a single polycistronic mRNA, the expression of envZ is known to be significantly less than ompR. However, to date no accurate estimation for the amounts of EnvZ and OmpR in the cell has been carried out. Here we examined the levels of EnvZ and OmpR in the wild-type strain MC4100 by quantitative Western blot analysis using anti-OmpR and anti-EnvZc (cytoplasmic domain of EnvZ) antisera. It was observed that during exponential growth in L-broth medium there were ∼3500 and 100 molecules per cell of OmpR and EnvZ, respectively. The levels of OmpR and EnvZ in MC4100 cells grown in a high osmolarity medium (nutrient broth with 20% sucrose) were about the same as those grown in L-broth, whereas they were 1.7-fold higher than those in a low osmolarity medium (nutrient broth). With His10-OmpR, we also determined that theK d value for the EnvZc-OmpR complex formation is 1.20 ± 0.17 μm. On the basis of these results, the molecular mechanism of osmoregulation of ompF andompC is discussed. His-Asp phosphorelay signal transduction system nitrilotriacetic acid nutrient broth outer membrane porin proteins 5′-adenylyl-β,γ-imidodiphosphate Bacteria primarily rely on the His-Asp phosphorelay signal transduction system (HAP system),1 or the two-component signal transduction system, to acclimate in response to the changes of environmental conditions (1Hoch J.A. Curr. Opin. Microbiol. 2000; 3: 165-170Crossref PubMed Scopus (626) Google Scholar, 2Stock A.M. Robinson V.L. Goudreau P.N. Annu. Rev. Biochem. 2000; 69: 183-215Crossref PubMed Scopus (2417) Google Scholar). The HAP system basically consists of a histidine kinase, which serves as a signal receptor, and its cognate response regulator, which regulates specific gene expression or mediates cellular locomotion (3Grebe T.W. Stock J.B. Adv. Microb. Physiol. 1999; 41: 139-227Crossref PubMed Google Scholar).One of most extensively studied HAP systems is the EnvZ/OmpR system mediating signal transduction in response to environmental osmolarity changes in Escherichia coli (4Egger L.A. Park H. Inouye M. Genes Cells. 1997; 2: 167-184Crossref PubMed Scopus (154) Google Scholar, 5Pratt L. Silhavy T.J. Hoch J. Silhavy T.J. Two-component Signal Transduction. American Society for Microbiology Press, Washington, D. C.1995: 105-107Google Scholar, 6Forst S.A. Roberts D.L. Res. Microbiol. 1994; 145: 363-373Crossref PubMed Scopus (113) Google Scholar). EnvZ, a histidine kinase, undergoestrans-autophosphorylation on the highly conserved His-243 residue (7Yang Y. Inouye M. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 11057-11061Crossref PubMed Scopus (144) Google Scholar, 8Yang Y. Inouye M. J. Mol. Biol. 1993; 231: 335-342Crossref PubMed Scopus (65) Google Scholar). The high energy phosphoryl group is subsequently transferred to the conserved Asp-55 residue of OmpR, a response regulator. Phosphorylated OmpR (OmpR-P) serves as a transcription factor differentially modulating the expression of the major outer membrane porin genes, ompC and ompF. OmpC and OmpF form channels in the outer membrane, which allow passive diffusion of small hydrophilic molecules of less than 650 Da in size (9Nikaido H. Vaara M. Microbiol. Rev. 1985; 49: 1-32Crossref PubMed Google Scholar). EnvZ also possesses the OmpR-P phosphatase activity to dephosphorylate OmpR-P. It has been proposed that osmotic signal regulates the ratio of the kinase to the phosphatase activity of EnvZ to modulate the level of cellular OmpR-P by primarily altering the phosphatase activity (10Jin T. Inouye M. J. Mol. Biol. 1993; 232: 484-492Crossref PubMed Scopus (72) Google Scholar). The cellular OmpR-P levels reciprocally regulate the transcription ofompF and ompC. At low medium osmolarity a reduced level of OmpR-P, due to the decreased kinase/phosphatase ratio of EnvZ, favors the transcription of ompF. At high medium osmolarity an elevated OmpR-P level, resulting from the increased kinase/phosphatase ratio of EnvZ, allows the activation ofompC transcription. On the other hand, more OmpR-P molecules bind to the ompF promoter upstream region causing repression of ompF expression.EnvZ, consisting of 450 amino acid residues, exists as a dimer located in the inner cytoplasmic membrane of E. coli. The cytoplasmic domain of EnvZ (residues 180–450), EnvZc, also exists as a dimer and consists of the linker region (residues 180–222), domain A (or DHp domain, residues 223–289) and domain B (or CA domain, residues 290–450). It possesses both kinase and phosphatase activities similar to the intact EnvZ (11Park H. Saha S.K. Inouye M. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 6728-6732Crossref PubMed Scopus (94) Google Scholar, 12Dutta R. Qin L. Inouye M. Mol. Microbiol. 1999; 34: 633-640Crossref PubMed Scopus (201) Google Scholar). The linker region is considered to play an important role in transducing the signal from the periplasmic receptor domain to the cytoplasmic catalytic domain (13Park H. Inouye M. J. Bacteriol. 1997; 179: 4382-4390Crossref PubMed Google Scholar). The NMR solution of both domain A and domain B been T. R. Park H. Saha S.K. Y. R. D. H. H. Inouye M. M. Biol. 1999; PubMed Scopus Google T. Saha S.K. R. D. Park H. R. Qin L. T. A.M. M. Inouye M. M. 1998; PubMed Scopus Google Scholar). has been that domain A by as the OmpR-P and has been proposed that the phosphatase activity of EnvZ is by the domain A and domain B Y. Qin L. T. Inouye M. Proc. Natl. Acad. Sci. U. S. A. 2000; PubMed Scopus Google response OmpR consists of an domain the highly conserved Asp-55 phosphorylation and a domain M. H. S. Y. T. PubMed Scopus Google Scholar). The are by a linker Silhavy T.J. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). The of the domain a E. Stock A.M. 1997; PubMed Scopus Google H. A. J. Y. T. Biol. 1997; PubMed Scopus Google Scholar). The phosphorylation of OmpR Asp-55 its for the upstream of the ompC A. J. Mol. Biol. 1998; PubMed Scopus Google Scholar, S. J. Inouye M. J. Bacteriol. PubMed Google Scholar, H. S. T. J. Biochem. PubMed Scopus Google Scholar, J. Mol. Biol. PubMed Scopus Google Scholar). The in that OmpR-P to the to region and ofompC and the to the region and the to region and of J. Mol. Biol. PubMed Scopus Google Scholar, Inouye M. J. Biol. PubMed Google Scholar, A. Inouye M. J. Biol. 1994; PubMed Google Scholar, Qin L. L.A. Inouye M. Genes Cells. 1998; 3: PubMed Scopus Google Scholar). OmpR of a L. Inouye M. J. Biol. PubMed Scopus Google Scholar). It has been that OmpR-P molecules bind to in a L. Inouye M. J. Biol. PubMed Scopus Google Scholar, E. Stock A.M. J. Mol. Biol. 1999; PubMed Scopus Google Scholar). The of OmpR-P to these are in a that OmpR-P to and whereas OmpR-P to other the upstream and are by OmpR-P A. J. Mol. Biol. 1998; PubMed Scopus Google Scholar, Qin L. L.A. Inouye M. Genes Cells. 1998; 3: PubMed Scopus Google ompB of E. coli is of genes, and which are as a polycistronic from a promoter located to gene Silhavy T.J. J. Mol. Biol. PubMed Scopus Google Scholar). It has been that significantly EnvZ molecules are with OmpR molecules in a and has been that there are about molecules of OmpR whereas there are molecules of EnvZ per cell L. Silhavy T.J. Hoch J. Silhavy T.J. Two-component Signal Transduction. American Society for Microbiology Press, Washington, D. C.1995: 105-107Google Scholar). we the cellular OmpR and EnvZ levels under growth conditions by quantitative Western blot also determined the of OmpR and EnvZ by using and the mechanism by which the EnvZ/OmpR system regulates the in E. the OmpR and EnvZ levels in E. grown in L-broth were determined to be and 100 molecules per respectively. OmpR and EnvZ levels were the same from cells grown in L-broth medium or in a high osmolarity medium 20% However, cells were grown in a low osmolarity medium both OmpR and EnvZ levels were about of those in the high osmolarity The mechanism for the expression of the ompB locus under to be The of locus has been the is by OmpR, the of J. Mol. Biol. PubMed Scopus Google Scholar). It be that under the growth conditions the ratio of OmpR to EnvZ was and OmpR molecules in EnvZ or in with EnvZ It has been that of OmpR is more than that of EnvZ using as a J. Bacteriol. PubMed Google Scholar). and genes are transcribed as a single polycistronic Silhavy T.J. J. Mol. Biol. PubMed Scopus Google the expression of the genes are differentially the level of J. Bacteriol. PubMed Google d value of and was 1.20 ± 0.17 under the conditions the cell is Escherichia coli and American Society of Washington, D. the cellular of OmpR and EnvZ were to be and respectively. on the basis of the d value of EnvZ molecules in a cell are to be with It is important to that as OmpR molecules in higher than EnvZ OmpR-P molecules on EnvZ are with OmpR molecules in the cytoplasmic It has been that OmpR-P has a higher for the ompF andompC promoter than OmpR, that the OmpR-P molecules the are to the ompC promoter they are from the EnvZ phosphatase activity L. T. Inouye M. Proc. Natl. Acad. Sci. U. S. A. Google Qin L. L.A. Inouye M. Genes Cells. 1998; 3: PubMed Scopus Google proposed that low OmpR-P to the and to and to resulting in ompF whereas high the of OmpR-P and for the ompF to be also by OmpR-P, resulting in the ofompC expression and repression of the expression ofompF and ompC is the medium to the and a of the were the OmpR-P were and whereas and the OmpR-P Qin L. L.A. Inouye M. Genes Cells. 1998; 3: PubMed Scopus Google that the OmpR was that these be in low osmolarity the phosphorylation of or OmpR-P of OmpR molecules in a cell OmpR molecules per be to the expression of whereas high osmolarity the phosphorylation of about or OmpR-P of OmpR molecules in a cell molecules per be to the expression ofompC and to the expression of ompF. the EnvZ or EnvZ per cell low osmolarity and 100 EnvZ or EnvZ per cell high osmolarity are to the ofompF and ompC. On the basis of OmpR amounts has been that the OmpR-P level high osmolarity was about higher than that low osmolarity S. J. A. Inouye M. J. Bacteriol. PubMed Google Scholar). that the cellular OmpR level is increased by more than high osmolarity than that low the OmpR-P level be increased more than high osmolarity in with the level of OmpR-P low the cell low osmolarity whereas high osmolarity resulting in more changes in the OmpR-P of the OmpR-P to for the expression of ompF and ompC high and low However, the of ompF andompC in the cell be more as there are the His-Asp phosphorelay systems J. Bacteriol. PubMed Google and other genes ompF and ompC are known to be by OmpR-P R. H. Mol. PubMed Scopus Google Scholar, S. Park J. Bacteriol. PubMed Google Scholar, Mol. Microbiol. 1998; PubMed Scopus Google similar quantitative Western blot analysis has been carried with the proteins in signal The cellular of the and were to be molecules per cell coli J.A. PubMed Scopus Google Scholar, J. Bacteriol. PubMed Google Scholar). is important to that to histidine whereas EnvZ to the major signal transducing in E. coli as of histidine in E. coli to T. Res. 1997; PubMed Scopus Google Scholar). are in regulating whereas regulate transcription of specific genes S. S. M. M. J. Bacteriol. PubMed Google Scholar). The is the to the cellular of a kinase and its cognate response regulator, that the kinase system is from the kinase system in EnvZ and OmpR-P is in the A a about the role of EnvZ phosphatase activity in osmoregulation L. J. Biol. PubMed Scopus Google Scholar). the OmpR-P with EnvZc, and these be The of the important the of EnvZ in the osmoregulation of ompC and ompF. Bacteria primarily rely on the His-Asp phosphorelay signal transduction system (HAP system),1 or the two-component signal transduction system, to acclimate in response to the changes of environmental conditions (1Hoch J.A. Curr. Opin. Microbiol. 2000; 3: 165-170Crossref PubMed Scopus (626) Google Scholar, 2Stock A.M. Robinson V.L. Goudreau P.N. Annu. Rev. Biochem. 2000; 69: 183-215Crossref PubMed Scopus (2417) Google Scholar). The HAP system basically consists of a histidine kinase, which serves as a signal receptor, and its cognate response regulator, which regulates specific gene expression or mediates cellular locomotion (3Grebe T.W. Stock J.B. Adv. Microb. Physiol. 1999; 41: 139-227Crossref PubMed Google Scholar). of most extensively studied HAP systems is the EnvZ/OmpR system mediating signal transduction in response to environmental osmolarity changes in Escherichia coli (4Egger L.A. Park H. Inouye M. Genes Cells. 1997; 2: 167-184Crossref PubMed Scopus (154) Google Scholar, 5Pratt L. Silhavy T.J. Hoch J. Silhavy T.J. Two-component Signal Transduction. American Society for Microbiology Press, Washington, D. C.1995: 105-107Google Scholar, 6Forst S.A. Roberts D.L. Res. Microbiol. 1994; 145: 363-373Crossref PubMed Scopus (113) Google Scholar). EnvZ, a histidine kinase, undergoestrans-autophosphorylation on the highly conserved His-243 residue (7Yang Y. Inouye M. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 11057-11061Crossref PubMed Scopus (144) Google Scholar, 8Yang Y. Inouye M. J. Mol. Biol. 1993; 231: 335-342Crossref PubMed Scopus (65) Google Scholar). The high energy phosphoryl group is subsequently transferred to the conserved Asp-55 residue of OmpR, a response regulator. Phosphorylated OmpR (OmpR-P) serves as a transcription factor differentially modulating the expression of the major outer membrane porin genes, ompC and ompF. OmpC and OmpF form channels in the outer membrane, which allow passive diffusion of small hydrophilic molecules of less than 650 Da in size (9Nikaido H. Vaara M. Microbiol. Rev. 1985; 49: 1-32Crossref PubMed Google Scholar). EnvZ also possesses the OmpR-P phosphatase activity to dephosphorylate OmpR-P. It has been proposed that osmotic signal regulates the ratio of the kinase to the phosphatase activity of EnvZ to modulate the level of cellular OmpR-P by primarily altering the phosphatase activity (10Jin T. Inouye M. J. Mol. Biol. 1993; 232: 484-492Crossref PubMed Scopus (72) Google Scholar). The cellular OmpR-P levels reciprocally regulate the transcription ofompF and ompC. At low medium osmolarity a reduced level of OmpR-P, due to the decreased kinase/phosphatase ratio of EnvZ, favors the transcription of ompF. At high medium osmolarity an elevated OmpR-P level, resulting from the increased kinase/phosphatase ratio of EnvZ, allows the activation ofompC transcription. On the other hand, more OmpR-P molecules bind to the ompF promoter upstream region causing repression of ompF EnvZ, consisting of 450 amino acid residues, exists as a dimer located in the inner cytoplasmic membrane of E. coli. The cytoplasmic domain of EnvZ (residues 180–450), EnvZc, also exists as a dimer and consists of the linker region (residues 180–222), domain A (or DHp domain, residues 223–289) and domain B (or CA domain, residues 290–450). It possesses both kinase and phosphatase activities similar to the intact EnvZ (11Park H. Saha S.K. Inouye M. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 6728-6732Crossref PubMed Scopus (94) Google Scholar, 12Dutta R. Qin L. Inouye M. Mol. Microbiol. 1999; 34: 633-640Crossref PubMed Scopus (201) Google Scholar). The linker region is considered to play an important role in transducing the signal from the periplasmic receptor domain to the cytoplasmic catalytic domain (13Park H. Inouye M. J. Bacteriol. 1997; 179: 4382-4390Crossref PubMed Google Scholar). The NMR solution of both domain A and domain B been T. R. Park H. Saha S.K. Y. R. D. H. H. Inouye M. M. Biol. 1999; PubMed Scopus Google T. Saha S.K. R. D. Park H. R. Qin L. T. A.M. M. Inouye M. M. 1998; PubMed Scopus Google Scholar). has been that domain A by as the OmpR-P and has been proposed that the phosphatase activity of EnvZ is by the domain A and domain B Y. Qin L. T. Inouye M. Proc. Natl. Acad. Sci. U. S. A. 2000; PubMed Scopus Google Scholar). The response OmpR consists of an domain the highly conserved Asp-55 phosphorylation and a domain M. H. S. Y. T. PubMed Scopus Google Scholar). The are by a linker Silhavy T.J. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). The of the domain a E. Stock A.M. 1997; PubMed Scopus Google H. A. J. Y. T. Biol. 1997; PubMed Scopus Google Scholar). The phosphorylation of OmpR Asp-55 its for the upstream of the ompC A. J. Mol. Biol. 1998; PubMed Scopus Google Scholar, S. J. Inouye M. J. Bacteriol. PubMed Google Scholar, H. S. T. J. Biochem. PubMed Scopus Google Scholar, J. Mol. Biol. PubMed Scopus Google Scholar). The in that OmpR-P to the to region and ofompC and the to the region and the to region and of J. Mol. Biol. PubMed Scopus Google Scholar, Inouye M. J. Biol. PubMed Google Scholar, A. Inouye M. J. Biol. 1994; PubMed Google Scholar, Qin L. L.A. Inouye M. Genes Cells. 1998; 3: PubMed Scopus Google Scholar). OmpR of a L. Inouye M. J. Biol. PubMed Scopus Google Scholar). It has been that OmpR-P molecules bind to in a L. Inouye M. J. Biol. PubMed Scopus Google Scholar, E. Stock A.M. J. Mol. Biol. 1999; PubMed Scopus Google Scholar). The of OmpR-P to these are in a that OmpR-P to and whereas OmpR-P to other the upstream and are by OmpR-P A. J. Mol. Biol. 1998; PubMed Scopus Google Scholar, Qin L. L.A. Inouye M. Genes Cells. 1998; 3: PubMed Scopus Google Scholar). The ompB of E. coli is of genes, and which are as a polycistronic from a promoter located to gene Silhavy T.J. J. Mol. Biol. PubMed Scopus Google Scholar). It has been that significantly EnvZ molecules are with OmpR molecules in a and has been that there are about molecules of OmpR whereas there are molecules of EnvZ per cell L. Silhavy T.J. Hoch J. Silhavy T.J. Two-component Signal Transduction. American Society for Microbiology Press, Washington, D. C.1995: 105-107Google Scholar). we the cellular OmpR and EnvZ levels under growth conditions by quantitative Western blot also determined the of OmpR and EnvZ by using and the mechanism by which the EnvZ/OmpR system regulates the in E. coli. the OmpR and EnvZ levels in E. grown in L-broth were determined to be and 100 molecules per respectively. OmpR and EnvZ levels were the same from cells grown in L-broth medium or in a high osmolarity medium 20% However, cells were grown in a low osmolarity medium both OmpR and EnvZ levels were about of those in the high osmolarity The mechanism for the expression of the ompB locus under to be The of locus has been the is by OmpR, the of J. Mol. Biol. PubMed Scopus Google Scholar). It be that under the growth conditions the ratio of OmpR to EnvZ was and OmpR molecules in EnvZ or in with EnvZ It has been that of OmpR is more than that of EnvZ using as a J. Bacteriol. PubMed Google Scholar). and genes are transcribed as a single polycistronic Silhavy T.J. J. Mol. Biol. PubMed Scopus Google the expression of the genes are differentially the level of J. Bacteriol. PubMed Google d value of and was 1.20 ± 0.17 under the conditions the cell is Escherichia coli and American Society of Washington, D. the cellular of OmpR and EnvZ were to be and respectively. on the basis of the d value of EnvZ molecules in a cell are to be with It is important to that as OmpR molecules in higher than EnvZ OmpR-P molecules on EnvZ are with OmpR molecules in the cytoplasmic It has been that OmpR-P has a higher for the ompF andompC promoter than OmpR, that the OmpR-P molecules the are to the ompC promoter they are from the EnvZ phosphatase activity L. T. Inouye M. Proc. Natl. Acad. Sci. U. S. A. Google Qin L. L.A. Inouye M. Genes Cells. 1998; 3: PubMed Scopus Google proposed that low OmpR-P to the and to and to resulting in ompF whereas high the of OmpR-P and for the ompF to be also by OmpR-P, resulting in the ofompC expression and repression of the expression ofompF and ompC is the medium to the and a of the were the OmpR-P were and whereas and the OmpR-P Qin L. L.A. Inouye M. Genes Cells. 1998; 3: PubMed Scopus Google that the OmpR was that these be in low osmolarity the phosphorylation of or OmpR-P of OmpR molecules in a cell OmpR molecules per be to the expression of whereas high osmolarity the phosphorylation of about or OmpR-P of OmpR molecules in a cell molecules per be to the expression ofompC and to the expression of ompF. the EnvZ or EnvZ per cell low osmolarity and 100 EnvZ or EnvZ per cell high osmolarity are to the ofompF and ompC. On the basis of OmpR amounts has been that the OmpR-P level high osmolarity was about higher than that low osmolarity S. J. A. Inouye M. J. Bacteriol. PubMed Google Scholar). that the cellular OmpR level is increased by more than high osmolarity than that low the OmpR-P level be increased more than high osmolarity in with the level of OmpR-P low the cell low osmolarity whereas high osmolarity resulting in more changes in the OmpR-P of the OmpR-P to for the expression of ompF and ompC high and low However, the of ompF andompC in the cell be more as there are the His-Asp phosphorelay systems J. Bacteriol. PubMed Google and other genes ompF and ompC are known to be by OmpR-P R. H. Mol. PubMed Scopus Google Scholar, S. Park J. Bacteriol. PubMed Google Scholar, Mol. Microbiol. 1998; PubMed Scopus Google similar quantitative Western blot analysis has been carried with the proteins in signal The cellular of the and were to be molecules per cell coli J.A. PubMed Scopus Google Scholar, J. Bacteriol. PubMed Google Scholar). is important to that to histidine whereas EnvZ to the major signal transducing in E. coli as of histidine in E. coli to T. Res. 1997; PubMed Scopus Google Scholar). are in regulating whereas regulate transcription of specific genes S. S. M. M. J. Bacteriol. PubMed Google Scholar). The is the to the cellular of a kinase and its cognate response regulator, that the kinase system is from the kinase system in EnvZ and OmpR-P is in the A a about the role of EnvZ phosphatase activity in osmoregulation L. J. Biol. PubMed Scopus Google Scholar). the OmpR-P with EnvZc, and these be The of the important the of EnvZ in the osmoregulation of ompC and ompF. the OmpR and EnvZ levels in E. grown in L-broth were determined to be and 100 molecules per respectively. OmpR and EnvZ levels were the same from cells grown in L-broth medium or in a high osmolarity medium 20% However, cells were grown in a low osmolarity medium both OmpR and EnvZ levels were about of those in the high osmolarity The mechanism for the expression of the ompB locus under to be The of locus has been the is by OmpR, the of J. Mol. Biol. PubMed Scopus Google Scholar). It be that under the growth conditions the ratio of OmpR to EnvZ was and OmpR molecules in EnvZ or in with EnvZ It has been that of OmpR is more than that of EnvZ using as a J. Bacteriol. PubMed Google Scholar). and genes are transcribed as a single polycistronic Silhavy T.J. J. Mol. Biol. PubMed Scopus Google the expression of the genes are differentially the level of J. Bacteriol. PubMed Google Scholar). The d value of and was 1.20 ± 0.17 under the conditions the cell is Escherichia coli and American Society of Washington, D. the cellular of OmpR and EnvZ were to be and respectively. on the basis of the d value of EnvZ molecules in a cell are to be with It is important to that as OmpR molecules in higher than EnvZ OmpR-P molecules on EnvZ are with OmpR molecules in the cytoplasmic It has been that OmpR-P has a higher for the ompF andompC promoter than OmpR, that the OmpR-P molecules the are to the ompC promoter they are from the EnvZ phosphatase activity L. T. Inouye M. Proc. Natl. Acad. Sci. U. S. A. Google Scholar). Qin L. L.A. Inouye M. Genes Cells. 1998; 3: PubMed Scopus Google proposed that low OmpR-P to the and to and to resulting in ompF whereas high the of OmpR-P and for the ompF to be also by OmpR-P, resulting in the ofompC expression and repression of the expression ofompF and ompC is the medium to the and a of the were the OmpR-P were and whereas and the OmpR-P Qin L. L.A. Inouye M. Genes Cells. 1998; 3: PubMed Scopus Google that the OmpR was that these be in low osmolarity the phosphorylation of or OmpR-P of OmpR molecules in a cell OmpR molecules per be to the expression of whereas high osmolarity the phosphorylation of about or OmpR-P of OmpR molecules in a cell molecules per be to the expression ofompC and to the expression of ompF. the EnvZ or EnvZ per cell low osmolarity and 100 EnvZ or EnvZ per cell high osmolarity are to the ofompF and ompC. On the basis of OmpR amounts has been that the OmpR-P level high osmolarity was about higher than that low osmolarity S. J. A. Inouye M. J. Bacteriol. PubMed Google Scholar). that the cellular OmpR level is increased by more than high osmolarity than that low the OmpR-P level be increased more than high osmolarity in with the level of OmpR-P low the cell low osmolarity whereas high osmolarity resulting in more changes in the OmpR-P of the OmpR-P to for the expression of ompF and ompC high and low However, the of ompF andompC in the cell be more as there are the His-Asp phosphorelay systems J. Bacteriol. PubMed Google and other genes ompF and ompC are known to be by OmpR-P R. H. Mol. PubMed Scopus Google Scholar, S. Park J. Bacteriol. PubMed Google Scholar, Mol. Microbiol. 1998; PubMed Scopus Google Scholar). A similar quantitative Western blot analysis has been carried with the proteins in signal The cellular of the and were to be molecules per cell coli J.A. PubMed Scopus Google Scholar, J. Bacteriol. PubMed Google Scholar). is important to that to histidine whereas EnvZ to the major signal transducing in E. coli as of histidine in E. coli to T. Res. 1997; PubMed Scopus Google Scholar). are in regulating whereas regulate transcription of specific genes S. S. M. M. J. Bacteriol. PubMed Google Scholar). The is the to the cellular of a kinase and its cognate response regulator, that the kinase system is from the kinase system in The EnvZ and OmpR-P is in the A a about the role of EnvZ phosphatase activity in osmoregulation L. J. Biol. PubMed Scopus Google Scholar). the OmpR-P with EnvZc, and these be The of the important the of EnvZ in the osmoregulation of ompC and ompF. Qin for and for are to and for of the