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Cloning

This year, we succeeded in cloning all missing parts required for our measuring system. While mPR Xl, mPR Dr, mig1, Padh1 and rox1 were available in pUC-IDT vector or pGEM T-easy vector from last year's iGEM-Team Tuebingen, Pfet3, Panb1, Psuc2 were cloned directly from yeast genome. Furthermore we used the fluorescent reporter protein mOrange (BBa_E2050) and the transcriptional terminator Tadh (BBa_K801012) from the parts registry. A galactose inducible promotor (BBa_J63006) from the registry was used to create some plasmids which we want to use for the characterization of some of our parts. The cloning of luciferase succeeded only shortly before wiki freeze. As a result, the assemblies requiring luciferase were not performed anymore.

Assembly

Our general assembly strategy is illustrated in fig. 1. The pRS vectors do not fit the RFC10 criteria and can therefore not be used the for 3A-Assembly. Instead we used the BioBrick RFC10 vector pTUM100 (BBa_K801000) which was kindly provided by the iGEM Team of the TU Munich to fuse promotor and coding sequence. pTUM100 is a high copy shuttle plasmid which is based on the commercially available pYES2 vector and contains the cyc1 transcription terminator after the BioBrick suffix. Thus we could use some of the pTUM constructs directly for characterization of our repressible promotors (Pfet-mOrange-pTUM100, Panb-mOrange-pTUM100, Psuc-mOrange-pTUM100, Padh-mOrange-pTUM100). The parts required for the next steps of characterization were equipped with a the transcriptional terminator Tadh by ligation into a pSB1C3 plasmid containing Tadh. The resulting assemblies were again BioBricks. These inserts were then ligated into the pRS shuttle vectors losing parts of their prefix and/or suffix. In total we have created 29 new plasmids!

Fig. 1: General assembly scheme: First, promoter and coding sequence were assembled in pTUM100 using the 3A-Assembly protocol. Constructs with the reporter mOrange were used for characterization directly. Subsequently, the promotor and the fused coding sequence are ligated into a pSB1C3 plasmid with the transcriptional terminator Tadh1. The resulting assemblies are again BioBricks. These inserts are then ligated into the pRS shuttle vectors losing parts of their prefix and/or suffix.

Readout

For the characterization of our repressible promotors Pfet3, Panb1 and Psuc2 we transformed pTUM100 constructs with mOrange under the control of the promotor of interest in the laboratory yeast strain w303. We used the constitutive promotor Padh1 (sequence identical with BBa_J63005) as positive control. The promoter activity was analysed qualitatively using fluorescence microscopy (fig. 2).

Fig. 2: Detection of mOrange expression in the fluorescence microscope. Non-transformed yeast was used as negative control. Fluorescence was detected using a RFP filter set (ET Bandpass 470/40, ET Bandpass 572/35).

Next, we established a protocol for quantitative read-out of mOrange fluorescence using the plate reader. We recorded an excitation spectrum of non-transformed yeast and yeast expressing mOrange measuring the emission at 581nm (+/- 25nm). Fig. 3 compares the excitation spectra with the ideal excitation spectrum of mOrange. While the fluorescence decreases with higher excitation wavelength for non-transformed yeast, the spectrum of yeast expressing mOrange has a similar shape than the ideal excitation spectrum.

Fig. 3: Excitation spectra of non-transformed w303 yeast (neg. control) and yeast expressing mOrange. Both spectra were recorded in the plate reader (Ex: 400nm-550nm +/-9nm, Em: 581nm +/-20nm). The excitation spectrum of mOrange is indicated by a dashed line (source: http://www.tsienlab.ucsd.edu/Documents/REF%20-%20Fluorophore%20Spectra.xls).

Repressible Promotors

Fig. 4: Basal expression level of mOrange under the control of the promotors Pfet3, Panb1 and Psuc2. Non-transformed yeast was used as negative control. Fluorescence was detected using a RFP filter set (ET Bandpass 470/40, ET Bandpass 572/35).