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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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DNA fragments containing the btuB promoter used for lacZ fusions. The btuB initiation codon ATG is located at nucleotide position +242. Asterisk indicates the first nucleotide of the btuB mRNA. The trmA (tRNA methyltransferase) gene is located upstream from btuB. It has no known effect on btuB expression.
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Figure 3: DNA fragments containing the btuB promoter used for lacZ fusions. The btuB initiation codon ATG is located at nucleotide position +242. Asterisk indicates the first nucleotide of the btuB mRNA. The trmA (tRNA methyltransferase) gene is located upstream from btuB. It has no known effect on btuB expression.

Mentions: To determine whether gadXY affects the transcription of btuB, the β-galactosidase reporter assay was performed. The 461-, 673-, 913-, and 1285-bp DNA fragments (Figure 3) containing the promoter of btuB were fused with the lacZ coding sequence to generate pCB461lacZ, pCB673lacZ, pCB913lacZ, and pCB1285lacZ, respectively. Each of these single copy plasmid together with pGAD10 or pGadXY was transformed into E. coli strain DH5α. The transformed cells were grown in LB medium with 50 μg/ml of chloramphenicol and ampicilin to OD600~0.8 then assayed for β-galactosidase activity as described by Miller [39]. The β-galactosidase activity of cells containing pGadXY and a pCB derivative with the btuB promoter-lacZ fusion was divided by that of cells containing the control plasmid pGAD10 and the same pCB derivative to determine the percent decrease in btuB promoter activity in the presence of gadXY. The btuB promoter in the 461-, 673-, 913-, and 1285-bp DNA fragment was found to be decreased by 45.7, 47.1, 54.5, and 56.7%, respectively in the presence of gadXY, and was about 6 fold more active in the 1285-bp fragment than in other fragments (Table 2).


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)

DNA fragments containing the btuB promoter used for lacZ fusions. The btuB initiation codon ATG is located at nucleotide position +242. Asterisk indicates the first nucleotide of the btuB mRNA. The trmA (tRNA methyltransferase) gene is located upstream from btuB. It has no known effect on btuB expression.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: DNA fragments containing the btuB promoter used for lacZ fusions. The btuB initiation codon ATG is located at nucleotide position +242. Asterisk indicates the first nucleotide of the btuB mRNA. The trmA (tRNA methyltransferase) gene is located upstream from btuB. It has no known effect on btuB expression.
Mentions: To determine whether gadXY affects the transcription of btuB, the β-galactosidase reporter assay was performed. The 461-, 673-, 913-, and 1285-bp DNA fragments (Figure 3) containing the promoter of btuB were fused with the lacZ coding sequence to generate pCB461lacZ, pCB673lacZ, pCB913lacZ, and pCB1285lacZ, respectively. Each of these single copy plasmid together with pGAD10 or pGadXY was transformed into E. coli strain DH5α. The transformed cells were grown in LB medium with 50 μg/ml of chloramphenicol and ampicilin to OD600~0.8 then assayed for β-galactosidase activity as described by Miller [39]. The β-galactosidase activity of cells containing pGadXY and a pCB derivative with the btuB promoter-lacZ fusion was divided by that of cells containing the control plasmid pGAD10 and the same pCB derivative to determine the percent decrease in btuB promoter activity in the presence of gadXY. The btuB promoter in the 461-, 673-, 913-, and 1285-bp DNA fragment was found to be decreased by 45.7, 47.1, 54.5, and 56.7%, respectively in the presence of gadXY, and was about 6 fold more active in the 1285-bp fragment than in other fragments (Table 2).

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