Team:Hong Kong HKUST/characterization/ef1a

Introduction

The constitutive human Elongation Factor-1alpha (EF-1alpha) Promoter regulates gene expression in mammalian cells. It is known that the CMV promoter is commonly used for constitutive expression, and here we introduce EF-1alpha promoter as an alternative mammalian promoter, which works in a wide range of cell types. The origin of this part is from Homo sapiens chromosome 6 genomic contig, GRCh37. p13.

In our characterization, the sequence of EF-1alpha Promoter was assembled in front of a GFP reporter (BBa_K648013) and hGH polyA terminator (BBa_K404108) using Freiburg’s RFC25 format. The EF-1alpha promoter-GFP was then transfected into HEK293FT cells and in vivo green fluorescence signal was observed under fluorescence microscope. The positive control was iDUET101a plasmid (Addgene Plasmid Number 17629) that contains EGFP reporter driven by an EF-1alpha promoter. A negative control was made by GFP generator that does not contain the EF-1alpha promoter. As a side by side comparison, a CMV promoter driven GFP reporter was also transfected, though a quantitative comparison between the two was not conducted in our characterization. Detailed protocols for our characterization work can be accessed via the link.

Characterization Procedure

1. Build:

- EF-1alpha characterization construct: EF-1alpha promoter – Green Fluorescence Protein (GFP) – hGH polyadenylation sequence (hGH pA) - pSB1C3 (BBa_K1119010 – BBa_K648013 – BBa_K404108 – pSB1C3)

- CMV comparison construct: CMV promoter – Green Fluorescence Protein (GFP) – hGH polyadenylation sequence (hGH pA) - pSB1C3 (BBa_K1119006 – BBa_K648013 – BBa_K404108 – pSB1C3)

- Negative control construct: GFP – hGH pA - pSB1C3 (BBa_K648013 – BBa_K404108 – pSB1C3)

2. Prepare iDUET101a (Addgene) in which EF-1alpha promoter was cloned from. This plasmid contains EF-1alpha promoter and EGFP reporter. We have transfected this plasmid for positive control for EF-1alpha characterization.

3. Culture HEK293FT cell line (see below)

4. Transfect EF-1alpha characterization construct, CMV construct, negative control and positive control plasmids in HEK293FT cell line.

5. Observe GFP signal under fluorescence microscope

Cell Culture and Transfection

We cultured HEK 293FT cells following American Type Culture Collection’s standard procedure, except that we used DMEM with 10% FBS and 1% penicillin/streptomycin in our culture medium. For transfection, we followed the manufacturer’s protocol of LipofectamineTM 2000 (Invitrogen) and used serum-free and antibiotics-free DMEM to form the DNA-lipofectamine complex.

Result

Figure 1: GFP signal of EF-1alpha observed. HEK293FT cells were transfected with iDUET101a (positive control), pEF-1alpha-GFP, pCMV-GFP (alternative mammalian constitutive promoter), and GFP without promoter. Cells transfected with pEF-1alpha-GFP showed weaker green signal compared to those with iDUET101a and pCMV-GFP. This result agreed with the result reported by Qin et al., that the EF-1alpha promoter gives weaker activity than CMV promoter in HEK293T cells. Our negative control, GFP without promoter did not give any GFP signal. Scale bar = 0.1mm

At the time of regional jamboree, no GFP signal could be observed in cells transfected with GFP reporter driven by EF-1alpha promoter. Originally, we thought that the sequence of EF-1alpha promoter cloned from iDUET101a contained the full functional promoter region annotated in pBudCE4.1 (Invitrogen). We believed that EF-1alpha did trigger transcription but failed to translate the GFP coding sequence due to insufficient 5’ untranslated region (UTR). After the regional jamboree, the promoter was re-cloned with additional 3' sequences after the identified TATA box to allow a longer 5’ untranslated region before the GFP coding DNA sequence. From the the results above, we believed that translation of GFP is successful this time.

Conclusion

The EF-1alpha promoter is fully functional and has a weaker transcriptional strength than the CMV promoter in HEK293FT cells.

Reference

Qin, Jane Yuxia, Li Zhang, et al. "Systematic Comparison of Constitutive Promoters and the Doxycycline-Inducible Promoter." PLoS ONE. 5.5 (2010) .

Zhou, B. Y., Ye, Z., Chen, G., Gao, Z. P., Zhang, Y. A., & Cheng, L. (2007). Inducible and reversible transgene expression in human stem cells after efficient and stable gene transfer. Stem Cells, 25(3), 779-789. doi:10.1634/stemcells.2006-0128