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From 2011.igem.org

This design assume that if a connection between B. Subtilis and E. Coli exists, it happens trhough the periplasm.

For this design, we first need to build a MBP- CMP+ E. Coli Strand. The over expression of CMP in the cell is used to shortcut the hierarchy in the sugar degradation in the cell because the IPTG in the medium would prevent the system to work. We need to grow the strands in a medium without maltose, and replicate the strand in a medium contaning the maltose.

The maltose transport from the periplasm into the cytoplasm of E. Coli requires the MBP (Maltose Binding Protein) to open the transporter that will import the maltose, and doing this, free the MalT transcription factor. In the presence of maltotriose, the free MalT will polymerase, trigerring an activation of several promoters in the cell, including the one of our reporter.

The principle is summed up in the following scheme:

This system is probably a bit difficult to be constructed, and assumes a lot of things we are far from be sure of.