As an extension of our basic part tfoX we created a full transcriptional unit enabling you to perform natural transformation in V. natriegens. First we started assembling a full transcriptional unit using a constitutive promoter. Therefore, we assembled tfoX together with the constitutive promoters J23100 or J23110 into a transcriptional unit by golden gate assembly. After transformation of this reactions into E. coli we were able to get colonies that seemed to be positive for the Lvl1 plasmids encoding tfoX because they showed the right size of fragment after plasmid preparation and test digestion, whenever we sent them for sequencing, some basepairs of the tfox gene were always missing (Figure 1).We suggest that these problems could be caused because Tfox could somehow ne toxic to E. coli cells. At this point of our project we realized how important it is to have well characterized, tight, inducible promoters for the usage in V. natriegens. In addition to constitutive promoters, the Marburg Collection contains the inducible promoters, pTet and pTrc. From our measurements of the promoter characterization, we learned that the pTet promoter is the tightest one showing the lowest value of Luminescence without induction (Figure 2). The pTet promoter can be induced by the tetracycline derivative anhydrotetracycline (ATc). ATc is much less cytotoxic than IPTG but still capable of binding and altering the structure of the repressor TetR, leading to release of the promoter and enabling transcription.
Using this suitable promoter for V. natriegens we successfully assembled a plasmid containing a full transcriptional unit with a pTet promoter and did not had any problems during the cloning process. By Test Digestion and sequencing we could prove, that now the sequence of Tfox was correct (Figure 3 and 4).As we have already shown in the chapter of our basic part, we were able to perform natural transformation using this plasmid and could demonstrate, that GFP which is encoded on pYTK is expressed by V. natriegens. Click here to learn more about how we used our best composite part in our project on the following sites in the Strain Engineering sub-project: