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Repression of btuB gene transcription in Escherichia coli by the GadX protein.

Lei GS, Syu WJ, Liang PH, Chak KF, Hu WS, Hu ST - BMC Microbiol. (2011)

Bottom Line: The lacZ reporter gene assay revealed that these two genes decreased the btuB promoter activity by approximately 50%, and the production of the BtuB protein was reduced by approximately 90% in the presence of a plasmid carrying both gadX and gadY genes in E. coli as determined by Western blotting.The results showed the transcription of gadX with 1.4-fold increase but the level of btuB was reduced to 57%.In conclusion, this study provides the first evidence that the expression of btuB gene is transcriptionally repressed by the acid responsive genes gadX and gadY.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Taipei, Taiwan.

ABSTRACT

Background: BtuB (B twelve uptake) is an outer membrane protein of Escherichia coli. It serves as a receptor for cobalamines uptake or bactericidal toxin entry. A decrease in the production of the BtuB protein would cause E. coli to become resistant to colicins. The production of BtuB has been shown to be regulated at the post-transcriptional level. The secondary structure of 5' untranslated region of btuB mRNA and the intracellular concentration of adenosylcobalamin (Ado-Cbl) would affect the translational efficiency and RNA stability of btuB gene. The transcriptional regulation of btuB expression is still unclear.

Results: To determine whether the btuB gene is also transcriptionally controlled by trans-acting factors, a genomic library was screened for clones that enable E. coli to grow in the presence of colicin E7, and a plasmid carrying gadX and gadY genes was isolated. The lacZ reporter gene assay revealed that these two genes decreased the btuB promoter activity by approximately 50%, and the production of the BtuB protein was reduced by approximately 90% in the presence of a plasmid carrying both gadX and gadY genes in E. coli as determined by Western blotting. Results of electrophoretic mobility assay and DNase I footprinting indicated that the GadX protein binds to the 5' untranslated region of the btuB gene. Since gadX and gadY genes are more highly expressed under acidic conditions, the transcriptional level of btuB in cells cultured in pH 7.4 or pH 5.5 medium was examined by quantitative real-time PCR to investigate the effect of GadX. The results showed the transcription of gadX with 1.4-fold increase but the level of btuB was reduced to 57%.

Conclusions: Through biological and biochemical analysis, we have demonstrated the GadX can directly interact with btuB promoter and affect the expression of btuB. In conclusion, this study provides the first evidence that the expression of btuB gene is transcriptionally repressed by the acid responsive genes gadX and gadY.

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Binding sequence of GadX on btuB promoter. (A) The 461-bp DNA fragment containing btuB promoter was labeled at 5' end with 32P, incubated with 0, 16, 24, 32, or 40 pmoles of MalE-GadX, and then subjected to DNase I footprinting. A Sanger's DNA sequencing reaction was also done on the 461-bp fragment to reveal GadX binding sequences. All reactions were electrophoresed in a 6% urea-acrylamide gel, and the DNA bands were detected by autoradiography. The GadX bound regions are indicated with vertical lines, and the binding sequence of GadX are shown. (B) Sequence of the btuB promoter region. The boxed sequences are GadX binding sequences determined by the DNase I footprinting. The shaded sequences are -10 and -35 regions of the btuB promoter. The initiation codon of btuB is underlined.
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Figure 5: Binding sequence of GadX on btuB promoter. (A) The 461-bp DNA fragment containing btuB promoter was labeled at 5' end with 32P, incubated with 0, 16, 24, 32, or 40 pmoles of MalE-GadX, and then subjected to DNase I footprinting. A Sanger's DNA sequencing reaction was also done on the 461-bp fragment to reveal GadX binding sequences. All reactions were electrophoresed in a 6% urea-acrylamide gel, and the DNA bands were detected by autoradiography. The GadX bound regions are indicated with vertical lines, and the binding sequence of GadX are shown. (B) Sequence of the btuB promoter region. The boxed sequences are GadX binding sequences determined by the DNase I footprinting. The shaded sequences are -10 and -35 regions of the btuB promoter. The initiation codon of btuB is underlined.

Mentions: DNase I footprinting was then performed to determine the binding sequence of GadX on the btuB promoter. The 461-bp DNA fragment containing the btuB promoter was labeled with 32P and incubated with 0, 2, 4, or 8 pmoles of purified MalE-GadX protein and then digested with DNase I. Results shown in Figure 5 revealed three MalE-GadX protein binding sites that included nucleotide positions +56 - +81 (I), +96 - +105 (II) and +123 - +137 (III) on the 5' untranslated region of btuB.


Repression of btuB gene transcription in Escherichia coli by the GadX protein.

Lei GS, Syu WJ, Liang PH, Chak KF, Hu WS, Hu ST - BMC Microbiol. (2011)

Binding sequence of GadX on btuB promoter. (A) The 461-bp DNA fragment containing btuB promoter was labeled at 5' end with 32P, incubated with 0, 16, 24, 32, or 40 pmoles of MalE-GadX, and then subjected to DNase I footprinting. A Sanger's DNA sequencing reaction was also done on the 461-bp fragment to reveal GadX binding sequences. All reactions were electrophoresed in a 6% urea-acrylamide gel, and the DNA bands were detected by autoradiography. The GadX bound regions are indicated with vertical lines, and the binding sequence of GadX are shown. (B) Sequence of the btuB promoter region. The boxed sequences are GadX binding sequences determined by the DNase I footprinting. The shaded sequences are -10 and -35 regions of the btuB promoter. The initiation codon of btuB is underlined.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3050690&req=5

Figure 5: Binding sequence of GadX on btuB promoter. (A) The 461-bp DNA fragment containing btuB promoter was labeled at 5' end with 32P, incubated with 0, 16, 24, 32, or 40 pmoles of MalE-GadX, and then subjected to DNase I footprinting. A Sanger's DNA sequencing reaction was also done on the 461-bp fragment to reveal GadX binding sequences. All reactions were electrophoresed in a 6% urea-acrylamide gel, and the DNA bands were detected by autoradiography. The GadX bound regions are indicated with vertical lines, and the binding sequence of GadX are shown. (B) Sequence of the btuB promoter region. The boxed sequences are GadX binding sequences determined by the DNase I footprinting. The shaded sequences are -10 and -35 regions of the btuB promoter. The initiation codon of btuB is underlined.
Mentions: DNase I footprinting was then performed to determine the binding sequence of GadX on the btuB promoter. The 461-bp DNA fragment containing the btuB promoter was labeled with 32P and incubated with 0, 2, 4, or 8 pmoles of purified MalE-GadX protein and then digested with DNase I. Results shown in Figure 5 revealed three MalE-GadX protein binding sites that included nucleotide positions +56 - +81 (I), +96 - +105 (II) and +123 - +137 (III) on the 5' untranslated region of btuB.

Bottom Line: The lacZ reporter gene assay revealed that these two genes decreased the btuB promoter activity by approximately 50%, and the production of the BtuB protein was reduced by approximately 90% in the presence of a plasmid carrying both gadX and gadY genes in E. coli as determined by Western blotting.The results showed the transcription of gadX with 1.4-fold increase but the level of btuB was reduced to 57%.In conclusion, this study provides the first evidence that the expression of btuB gene is transcriptionally repressed by the acid responsive genes gadX and gadY.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Taipei, Taiwan.

ABSTRACT

Background: BtuB (B twelve uptake) is an outer membrane protein of Escherichia coli. It serves as a receptor for cobalamines uptake or bactericidal toxin entry. A decrease in the production of the BtuB protein would cause E. coli to become resistant to colicins. The production of BtuB has been shown to be regulated at the post-transcriptional level. The secondary structure of 5' untranslated region of btuB mRNA and the intracellular concentration of adenosylcobalamin (Ado-Cbl) would affect the translational efficiency and RNA stability of btuB gene. The transcriptional regulation of btuB expression is still unclear.

Results: To determine whether the btuB gene is also transcriptionally controlled by trans-acting factors, a genomic library was screened for clones that enable E. coli to grow in the presence of colicin E7, and a plasmid carrying gadX and gadY genes was isolated. The lacZ reporter gene assay revealed that these two genes decreased the btuB promoter activity by approximately 50%, and the production of the BtuB protein was reduced by approximately 90% in the presence of a plasmid carrying both gadX and gadY genes in E. coli as determined by Western blotting. Results of electrophoretic mobility assay and DNase I footprinting indicated that the GadX protein binds to the 5' untranslated region of the btuB gene. Since gadX and gadY genes are more highly expressed under acidic conditions, the transcriptional level of btuB in cells cultured in pH 7.4 or pH 5.5 medium was examined by quantitative real-time PCR to investigate the effect of GadX. The results showed the transcription of gadX with 1.4-fold increase but the level of btuB was reduced to 57%.

Conclusions: Through biological and biochemical analysis, we have demonstrated the GadX can directly interact with btuB promoter and affect the expression of btuB. In conclusion, this study provides the first evidence that the expression of btuB gene is transcriptionally repressed by the acid responsive genes gadX and gadY.

Show MeSH
Related in: MedlinePlus