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Engineering and Validation of a Vector for Concomitant Expression of Rare Transfer RNA (tRNA) and HIV-1 nef Genes in Escherichia coli.

Mualif SA, Teow SY, Omar TC, Chew YW, Yusoff NM, Ali SA - PLoS ONE (2015)

Bottom Line: These codon bias -associated problems are addressed by co-expressing ColE1-compatible, rare tRNA expressing helper plasmids.To maintain the overall size of the parental plasmid vector, the rare tRNA genes replaced the non-essential DNA segments in the vector.We have evaluated the usefulness of this expression vector by expressing three HIV-1 genes namely HIV-1 p27 (nef), HIV-1 p24 (ca), and HIV-1 vif in NiCo21(DE3) E.coli and demonstrated the advantages of using expression vector that concomitantly expresses rare tRNA and heterologous genes.

View Article: PubMed Central - PubMed

Affiliation: Oncological and Radiological Sciences, Advanced Medical and Dental Institute, Universiti Sains Malaysia, Pulau Pinang, Malaysia.

ABSTRACT
Relative ease in handling and manipulation of Escherichia coli strains make them primary candidate to express proteins heterologously. Overexpression of heterologous genes that contain codons infrequently used by E. coli is related with difficulties such as mRNA instability, early termination of transcription and/or translation, deletions and/or misincorporation, and cell growth inhibition. These codon bias -associated problems are addressed by co-expressing ColE1-compatible, rare tRNA expressing helper plasmids. However, this approach has inadequacies, which we have addressed by engineering an expression vector that concomitantly expresses the heterologous protein of interest, and rare tRNA genes in E. coli. The expression vector contains three (argU, ileY, leuW) rare tRNA genes and a useful multiple cloning site for easy in-frame cloning. To maintain the overall size of the parental plasmid vector, the rare tRNA genes replaced the non-essential DNA segments in the vector. The cloned gene is expressed under the control of T7 promoter and resulting recombinant protein has a C-terminal 6His tag for IMAC-mediated purification. We have evaluated the usefulness of this expression vector by expressing three HIV-1 genes namely HIV-1 p27 (nef), HIV-1 p24 (ca), and HIV-1 vif in NiCo21(DE3) E.coli and demonstrated the advantages of using expression vector that concomitantly expresses rare tRNA and heterologous genes.

No MeSH data available.


Related in: MedlinePlus

Expression of Nef from pSA-HNef-6His vectors with or without rare tRNA genes array.To evaluate the effect of the introduction of rare tRNA genes array in pSA-HNef-6His vector, the NiCo21 E. coli were individually transformed with pSA-HNef-6His, pSA-HNef-6His-RIL(CW), and pSA-HNef-6His-RIL(CCW) and Nef expression was compared with NiCo21 E. coli co-transformed with pSA-HNef-6His and rare tRNA expressing pACYC-RIL vectors. The cultures were grown overnight at 30°C in LB broth containing Amp (for bacteria harboring pSA-HNef-6His or pSA-HNef-6His-RIL) or Amp+Cam (for bacteria harboring pSA-HNef-6His + pACYC-RIL). The cultures were then diluted 100-fold in the same medium and grown to mid-log phase (OD600 ~0.5–0.6), at which point IPTG was added to a final concentration of 0.05 mM. The induced cells were grown for another 12 h at 22°C and stored on ice. Nine microliters of samples were mixed with 4 x loading dye, electrophoretically resolved on a 15% SDS-PAGE gel and analyzed by (A) Coomassie staining, (B) immuno-blotting and (C) band densitometry. Nef expression in NiCo21 transformed with pSA-HNef-6His-RIL (CW/CCW) was comparable with NiCo21 co-transformed with pSA-HNef-6His and pACYC-RIL. A prominent band running at 25 kDa (red arrows) appears in NiCo21 harboring pSA-HNef-6His/ pACYC-RIL. This is most probably chloramphenicol acetyltransferase monomer. Higher baseline expression for un-induced cultures were noted in NiCo21 harboring pSA-HNef-6His-RIL(CCW) (see green arrows). This suggests that ileY tRNA gene most probably doesn’t contain a transcription terminator downstream and the baseline expression of Nef is a result of transcriptional read-through of mRNA synthesis from ileY promoter.
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pone.0130446.g006: Expression of Nef from pSA-HNef-6His vectors with or without rare tRNA genes array.To evaluate the effect of the introduction of rare tRNA genes array in pSA-HNef-6His vector, the NiCo21 E. coli were individually transformed with pSA-HNef-6His, pSA-HNef-6His-RIL(CW), and pSA-HNef-6His-RIL(CCW) and Nef expression was compared with NiCo21 E. coli co-transformed with pSA-HNef-6His and rare tRNA expressing pACYC-RIL vectors. The cultures were grown overnight at 30°C in LB broth containing Amp (for bacteria harboring pSA-HNef-6His or pSA-HNef-6His-RIL) or Amp+Cam (for bacteria harboring pSA-HNef-6His + pACYC-RIL). The cultures were then diluted 100-fold in the same medium and grown to mid-log phase (OD600 ~0.5–0.6), at which point IPTG was added to a final concentration of 0.05 mM. The induced cells were grown for another 12 h at 22°C and stored on ice. Nine microliters of samples were mixed with 4 x loading dye, electrophoretically resolved on a 15% SDS-PAGE gel and analyzed by (A) Coomassie staining, (B) immuno-blotting and (C) band densitometry. Nef expression in NiCo21 transformed with pSA-HNef-6His-RIL (CW/CCW) was comparable with NiCo21 co-transformed with pSA-HNef-6His and pACYC-RIL. A prominent band running at 25 kDa (red arrows) appears in NiCo21 harboring pSA-HNef-6His/ pACYC-RIL. This is most probably chloramphenicol acetyltransferase monomer. Higher baseline expression for un-induced cultures were noted in NiCo21 harboring pSA-HNef-6His-RIL(CCW) (see green arrows). This suggests that ileY tRNA gene most probably doesn’t contain a transcription terminator downstream and the baseline expression of Nef is a result of transcriptional read-through of mRNA synthesis from ileY promoter.

Mentions: We expressed Nef in E. coli transformed with pSA-HNef-6His-RIL(CW)/(CCW) and compared Nef production with E. coli transformed with pSA-HNef-6His (served as negative control), and pSA-HNef-6His together with pACYC-RIL (served as positive control). Expression experiments were carried out using shaker flask culture conditions for expression as described above. When subjected to SDS-PAGE analysis, Nef expression in bacteria containing pSA-HNef-6His-RIL was comparable with those that contained both pSA-HNef-6His and pACYC-RIL. Little Nef produced in bacteria that harbored pSA-HNef-6His vector (Fig 6A). There was noticeable background expression in un-induced cultures from pSA-HNef-6His-RIL (CW) compared to pSA-HNef-6His-RIL (CCW) (green arrow, Fig 6A and 6B). This suggests that in addition to T7 promoter, Nef was also expressed under the control of some promoter upstream of T7 promoter, most likely of ileY (Fig 5B). As a result, the pSA-HNef-6His-RIL(CCW) was not used in subsequent expression experiments. Samples from pSA-HNef-6His+pACYC-RIL showed a prominent 25kDa band present in both un-induced, and IPTG-induced cultures (red arrows, Fig 6A). This band most probably represents chloramphenicol acetyltransferase monomer expressed from pACYC-RIL vector. Proteins were also subjected to immunoblot analysis (Fig 6B) using anti-Nef MAb as primary antibody and relative band intensities were determined and plotted as shown in Fig 6C. Together, these experiments show that recombinant protein can be produced from a single vector concomitantly expressing rare tRNA and a heterologous gene, and in amounts comparable (or better) to traditional two-vector system.


Engineering and Validation of a Vector for Concomitant Expression of Rare Transfer RNA (tRNA) and HIV-1 nef Genes in Escherichia coli.

Mualif SA, Teow SY, Omar TC, Chew YW, Yusoff NM, Ali SA - PLoS ONE (2015)

Expression of Nef from pSA-HNef-6His vectors with or without rare tRNA genes array.To evaluate the effect of the introduction of rare tRNA genes array in pSA-HNef-6His vector, the NiCo21 E. coli were individually transformed with pSA-HNef-6His, pSA-HNef-6His-RIL(CW), and pSA-HNef-6His-RIL(CCW) and Nef expression was compared with NiCo21 E. coli co-transformed with pSA-HNef-6His and rare tRNA expressing pACYC-RIL vectors. The cultures were grown overnight at 30°C in LB broth containing Amp (for bacteria harboring pSA-HNef-6His or pSA-HNef-6His-RIL) or Amp+Cam (for bacteria harboring pSA-HNef-6His + pACYC-RIL). The cultures were then diluted 100-fold in the same medium and grown to mid-log phase (OD600 ~0.5–0.6), at which point IPTG was added to a final concentration of 0.05 mM. The induced cells were grown for another 12 h at 22°C and stored on ice. Nine microliters of samples were mixed with 4 x loading dye, electrophoretically resolved on a 15% SDS-PAGE gel and analyzed by (A) Coomassie staining, (B) immuno-blotting and (C) band densitometry. Nef expression in NiCo21 transformed with pSA-HNef-6His-RIL (CW/CCW) was comparable with NiCo21 co-transformed with pSA-HNef-6His and pACYC-RIL. A prominent band running at 25 kDa (red arrows) appears in NiCo21 harboring pSA-HNef-6His/ pACYC-RIL. This is most probably chloramphenicol acetyltransferase monomer. Higher baseline expression for un-induced cultures were noted in NiCo21 harboring pSA-HNef-6His-RIL(CCW) (see green arrows). This suggests that ileY tRNA gene most probably doesn’t contain a transcription terminator downstream and the baseline expression of Nef is a result of transcriptional read-through of mRNA synthesis from ileY promoter.
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Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4492947&req=5

pone.0130446.g006: Expression of Nef from pSA-HNef-6His vectors with or without rare tRNA genes array.To evaluate the effect of the introduction of rare tRNA genes array in pSA-HNef-6His vector, the NiCo21 E. coli were individually transformed with pSA-HNef-6His, pSA-HNef-6His-RIL(CW), and pSA-HNef-6His-RIL(CCW) and Nef expression was compared with NiCo21 E. coli co-transformed with pSA-HNef-6His and rare tRNA expressing pACYC-RIL vectors. The cultures were grown overnight at 30°C in LB broth containing Amp (for bacteria harboring pSA-HNef-6His or pSA-HNef-6His-RIL) or Amp+Cam (for bacteria harboring pSA-HNef-6His + pACYC-RIL). The cultures were then diluted 100-fold in the same medium and grown to mid-log phase (OD600 ~0.5–0.6), at which point IPTG was added to a final concentration of 0.05 mM. The induced cells were grown for another 12 h at 22°C and stored on ice. Nine microliters of samples were mixed with 4 x loading dye, electrophoretically resolved on a 15% SDS-PAGE gel and analyzed by (A) Coomassie staining, (B) immuno-blotting and (C) band densitometry. Nef expression in NiCo21 transformed with pSA-HNef-6His-RIL (CW/CCW) was comparable with NiCo21 co-transformed with pSA-HNef-6His and pACYC-RIL. A prominent band running at 25 kDa (red arrows) appears in NiCo21 harboring pSA-HNef-6His/ pACYC-RIL. This is most probably chloramphenicol acetyltransferase monomer. Higher baseline expression for un-induced cultures were noted in NiCo21 harboring pSA-HNef-6His-RIL(CCW) (see green arrows). This suggests that ileY tRNA gene most probably doesn’t contain a transcription terminator downstream and the baseline expression of Nef is a result of transcriptional read-through of mRNA synthesis from ileY promoter.
Mentions: We expressed Nef in E. coli transformed with pSA-HNef-6His-RIL(CW)/(CCW) and compared Nef production with E. coli transformed with pSA-HNef-6His (served as negative control), and pSA-HNef-6His together with pACYC-RIL (served as positive control). Expression experiments were carried out using shaker flask culture conditions for expression as described above. When subjected to SDS-PAGE analysis, Nef expression in bacteria containing pSA-HNef-6His-RIL was comparable with those that contained both pSA-HNef-6His and pACYC-RIL. Little Nef produced in bacteria that harbored pSA-HNef-6His vector (Fig 6A). There was noticeable background expression in un-induced cultures from pSA-HNef-6His-RIL (CW) compared to pSA-HNef-6His-RIL (CCW) (green arrow, Fig 6A and 6B). This suggests that in addition to T7 promoter, Nef was also expressed under the control of some promoter upstream of T7 promoter, most likely of ileY (Fig 5B). As a result, the pSA-HNef-6His-RIL(CCW) was not used in subsequent expression experiments. Samples from pSA-HNef-6His+pACYC-RIL showed a prominent 25kDa band present in both un-induced, and IPTG-induced cultures (red arrows, Fig 6A). This band most probably represents chloramphenicol acetyltransferase monomer expressed from pACYC-RIL vector. Proteins were also subjected to immunoblot analysis (Fig 6B) using anti-Nef MAb as primary antibody and relative band intensities were determined and plotted as shown in Fig 6C. Together, these experiments show that recombinant protein can be produced from a single vector concomitantly expressing rare tRNA and a heterologous gene, and in amounts comparable (or better) to traditional two-vector system.

Bottom Line: These codon bias -associated problems are addressed by co-expressing ColE1-compatible, rare tRNA expressing helper plasmids.To maintain the overall size of the parental plasmid vector, the rare tRNA genes replaced the non-essential DNA segments in the vector.We have evaluated the usefulness of this expression vector by expressing three HIV-1 genes namely HIV-1 p27 (nef), HIV-1 p24 (ca), and HIV-1 vif in NiCo21(DE3) E.coli and demonstrated the advantages of using expression vector that concomitantly expresses rare tRNA and heterologous genes.

View Article: PubMed Central - PubMed

Affiliation: Oncological and Radiological Sciences, Advanced Medical and Dental Institute, Universiti Sains Malaysia, Pulau Pinang, Malaysia.

ABSTRACT
Relative ease in handling and manipulation of Escherichia coli strains make them primary candidate to express proteins heterologously. Overexpression of heterologous genes that contain codons infrequently used by E. coli is related with difficulties such as mRNA instability, early termination of transcription and/or translation, deletions and/or misincorporation, and cell growth inhibition. These codon bias -associated problems are addressed by co-expressing ColE1-compatible, rare tRNA expressing helper plasmids. However, this approach has inadequacies, which we have addressed by engineering an expression vector that concomitantly expresses the heterologous protein of interest, and rare tRNA genes in E. coli. The expression vector contains three (argU, ileY, leuW) rare tRNA genes and a useful multiple cloning site for easy in-frame cloning. To maintain the overall size of the parental plasmid vector, the rare tRNA genes replaced the non-essential DNA segments in the vector. The cloned gene is expressed under the control of T7 promoter and resulting recombinant protein has a C-terminal 6His tag for IMAC-mediated purification. We have evaluated the usefulness of this expression vector by expressing three HIV-1 genes namely HIV-1 p27 (nef), HIV-1 p24 (ca), and HIV-1 vif in NiCo21(DE3) E.coli and demonstrated the advantages of using expression vector that concomitantly expresses rare tRNA and heterologous genes.

No MeSH data available.


Related in: MedlinePlus