The tolB effect appears to be specific to the ugd gene because transcription of the PhoP-activated PmrA-dependent pbgP gene and the PhoP-activated PmrA-independent mgtA gene was not affected by the tolB mutation regardless of the presence of functional phoP or pmrA genes ( Fig. 2A ; data not shown ) .
b-Galactosidase activity ( Miller units ) expressed by strains grown in LB-medium was determined for strains harbouring lac transcriptional-fusions to the PhoP-activated PmrA-dependent ugd ( A -- C ) and pbgP ( A ) genes , and the PhoP-activated PmrA-independent mgtA gene ( A ) .
D. Alignment of the regulatory sequences of the PhoP-activated ugd , phoP , mgtA and mgrB genes .
To examine the effects of the PhoQ-T48X mutations on the entire PhoP/PhoQ signaling pathway in-vivo , we measured the expression of mgtA ( a PhoP-activated gene that encodes a Mg2 transporter ) by measuring the-ga-lactosidase activity of the mgtA : : lacZ-transcriptional-fusion ( 18 ) .
To examine the effects of the PhoQ-T48X mutations on the entire PhoP/PhoQ signaling pathway in-vivo , we measured the expression of mgtA ( a PhoP-activated gene that encodes a Mg2 transporter ) by measuring the-ga-lactosidase activity of the mgtA : : lacZ-transcriptional-fusion ( 18 ) .
We have investigated the transcriptional regulation and the interaction of the response regulator PhoP with the promoter regions of the PhoP-activated loci phoPQ , mgtA , slyB , pmrD , pcgL , phoN , pagC , and mgtCB .
Indeed , experiments carried out with the PhoP-activated mgtA promoter of Escherichia coli demonstrated the critical role that certain PhoP box nucleotides play in mgtA expression and that the purified PhoP protein and RNA polymerase were sufficient to promote mgtA transcription in-vitro ( 13 ) .
We first examined the effect of the C-terminal His tag on PhoQ activity in-vivo by measuring the expression of mgtA ( a PhoP-activated gene that encodes an Mg2 + transporter ) through the β-galactosidase activity of an mgtA : : lacZ-transcriptional-fusion [ 15 ] .
We first examined the effect of the C-terminal His tag on PhoQ activity in-vivo by measuring the expression of mgtA ( a PhoP-activated gene that encodes an Mg2 + transporter ) through the β-galactosidase activity of an mgtA : : lacZ-transcriptional-fusion [ 15 ] .
PhoP-suppressed genes include prgH and fliC [ 55 -- 57 ] , PhoP-activated genes include pmrAB , another two-component signal transduction system involved primarily in the protection of Salmo-nella to cationic antimicrobial peptides ( CAMP , see below ) [ 58 ] , mgtA and mgtCB encoding Mg transport 2 + systems , phoN , a periplasmic non-specific acid phospha-tase , pcgL encoding a periplasmic D-Ala -- D-Ala dipeptidase , or pagL , pagP and pgtE which contribute to increased resistance to CAMPs [ 59 -- 62 ] .
$ , PhoP ; # , PhoP ~ P ; & , PhoPHis ; % , PhoPHis ~ P. Response ( RU DNA binding of PhoP proteins by SPR A BIAcore biosensor was used to examine , in real-time , the binding of the various PhoP proteins to the promoter of mgtA ( a PhoP-activated gene that contains a PhoP box in its promoter ) .
The mRNA lev - encoded products are produced in the correct els of the PhoP-activated mgtA , phoP , pmrD , locales , at the required amounts and for the ap - and mig-14 genes increased after the shift to low propriate extents of time .
Inactivation of the phoP or levels of the PhoP-activated genes increased , phoQ genes renders Salmonella enterica serovar reached a peak that was lower than that obtained Typhimurium five orders of magnitude less when Salmonella was induced at 50 mM Mg2 + virulent for mice and unable to proliferate within ( except for the mgtA gene , which reached the phagocytic cells ( 4-6 ) .
Recently , it has been shown that high-level expression of the Rob protein , results in the induction of the mgtA gene from a PhoP-independent promoter .
As shown in Fig. 4C , this motif is also observed in a similar position and in the same orientation in a subset of PhoP-activated genes , including phoP , mgtA , pmrD , yrbL , slyB , and orgB ( 49 ) .
This behavior reflects : first , that the PhoP-activated regulator RstA is necessary for transcription of feoB but not of mgtA in mildly acidic pH ( Choi , et al. , 2009 ) .
Moreover , deletion of the mgtA gene did not decrease the levels of PhoP-activated mRNAs in a strain with a PhoQ variant that is blind to periplasmic Mg2 + ( Fig. 4 ) .
Distinct temporal expression of PhoP-activated genes in response to mildly acidic pH and low Mg2 + he MgtA protein is necessary for full transcription of a subset of PhoP-activated genes hen the PhoQ inducing signal is low Mg2 + T w Wild-type and mgtA strains had similar pagC and pagK mRNA levels at 2 h post induction ( Fig. 2A ) ( i.e. , ratio of wild-type/mgtA of 1 ) .
Therefore , the mgtA requirement for normal expression of a subset of PhoP-activated genes does not result from inefficient transcription of the autoregulated phoP gene ( Soncini et al. , 1995 ) in the mgtA mutant ( Fig .
Therefore , the mgtA requirement for normal expression of a subset of PhoP-activated genes does not result from inefficient transcription of the autoregulated phoP gene ( Soncini et al. , 1995 ) in the mgtA mutant ( Fig .
MgtA 
If MgtA exerts its regulatory function by removing Mg2 + away from PhoQ , deletion of the mgtA gene should not affect expression of PhoP-activated genes in a strain lacking the phoQ gene .
19 additional genes _ known to be directly activated by the PhoP protein in mgtA strains following a 4 h incubation in 10 μM Mg
19 additional genes _ known to be directly activated by the PhoP protein in mgtA strains following a 4 h incubation in 10 μM Mg
A similar motif is found in the promoters of a subset of PhoP-activated genes , including steA , phoP , mgtA , pmrD , slyB , and orgB ( Fig. 6B ) .
The PhoP-activated mgtA gene specifies a Mg2 + transporter that enhances PhoP-P levels by transporting Mg2 + away from the periplasm , where it acts as an inhibitory signal for PhoQ ( 16 ) .
This regulatory architecture defines a two-tier structure among PhoP-activated genes based on whether they require mgtA for maximal expression ( 16 ) .
The PhoP-activated genes most dependent on the MgtA protein specify proteins of unknown function and , like the mgtA gene , are not required for virulence in an animal ( 19 -- 21 ) .
This motility requires the PhoP-activated mgtA , mgtC , and pagM genes , which specify a Mg2 + transporter , an inhibitor of Salmonella 
Transcription of the PhoP-activated phoP and mgtA genes was higher in wild-type S. enterica than in strains expressing the cadAB genes constitutively when the inducing condition was acidic pH ( Fig. 6C and D ) .