Part:BBa_K5317008

MREwt promoter-EGFP

Usage and Biology

The MRE-sites containing promoter enables the metal-dependent expression of a downstream positioned reporter gene EGFP via the metal ion-dependent transcription factor MTF-1 for cell-based metal detection.

The varying Metal Responsive Elements (MREs) upstream of the eukaryotic metallothionein (MT) gene were discovered in the early 80s (Carter et al. 1984, Stuart et al. 1985). All MREs a-d carry core consensus sites (TGCRCNC) to which the primary MRE-binding transcription factor MTF-1 can bind after binding to heavy metal ions and translocating into the nucleus (Wang et al. 2004). Physiologically, this leads to the expression of metallothionein, a protein capable of binding metals such as zinc, cadmium, copper and others for metal homeostasis and detoxification (Cousins 1983). The arrangement of the MREs in our promoter construct was inspired by publications from Glanville et al. (1981) and Searle et al. (1985), maintaining the order of MREs from the physiological murine MT-1 promoter.

Cloning

Theoretical Part Design

Placing the MRE containing promoter upstream of the reporter gene EGFP allows the visualization of primarily metal-dependent activation of MTF-1.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]

Cloning

Therefore, the promoter was synthesized and inserted by NEB HiFi Assembly into the pEGFP-C2 backbone plasmid (K3338020) after its restriction enzyme digestion with AseI and NheI, generating the MREwt-EGFP cassette. Table1: Primers used to extract the MTF-1 gene sequence.

Primer name	Sequence
MTF1_fw	CAGAGCTGGTTTAGTGAACCGTCAGATCCGATGGGGGAACACAGTCCAGAC
MTF1_rv	gatcccccCTAGGGTGGCAGCTGCAG

The vector map of the assembled construct is shown in figure 1.

Characterization

Transfection experiments in mammalian HEK293T cells assessed the promoter functionality and sensitivity. First, the composite part carrying plasmid was introduced via transfection to establish a baseline of endogenous promoter activity before performing co-transfection experiments with the MTF-1-mRuby carrying plasmid (composite part ___) under varying copper concentration for stimulation. The EGFP fluorescence signal was analyzed for localization by microscopy and intensity by FACS analysis.

References

Carter, A. D., Felber, B. K., Walling, M. J., Jubier, M. F., Schmidt, C. J., & Hamer, D. H. (1984). Duplicated heavy metal control sequences of the mouse metallothionein-I gene. Proceedings of the National Academy of Sciences of the United States of America, 81(23), 7392–7396. https://doi.org/10.1073/pnas.81.23.7392

Cousins R. J. (1983). Metallothionein--aspects related to copper and zinc metabolism. Journal of inherited metabolic disease, 6 Suppl 1, 15–21. https://doi.org/10.1007/BF01811318

Glanville, N., Durnam, D. M., & Palmiter, R. D. (1981). Structure of mouse metallothionein-I gene and its mRNA. Nature, 292(5820), 267–269. https://doi.org/10.1038/292267a0

Searle, P. F., Stuart, G. W., & Palmiter, R. D. (1985). Building a metal-responsive promoter with synthetic regulatory elements. Molecular and cellular biology, 5(6), 1480–1489. https://doi.org/10.1128/mcb.5.6.1480-1489.1985

Stuart, G. W., Searle, P. F., & Palmiter, R. D. (1985). Identification of multiple metal regulatory elements in mouse metallothionein-I promoter by assaying synthetic sequences. Nature, 317(6040), 828–831. https://doi.org/10.1038/317828a0#

Wang, Y., Lorenzi, I., Georgiev, O., & Schaffner, W. (2004). Metal-responsive transcription factor-1 (MTF-1) selects different types of metal response elements at low vs. high zinc concentration. Biological chemistry, 385(7), 623–632. https://doi.org/10.1515/BC.2004.077