Figure 9.

Schematic of the O_RO_lac engineered promoter. The promoter fuses three operator sites, one of which (O_lac) yields repression when the LacI tetramer is bound to it, while binding of the CI dimer to O_R2 yields approximately ten-fold activation (the O_R1 site assists activation by cooperatively enhancing CI binding to O_R2 when CI is bound to O_R1). In the experimental system, CI and LacI are produced in the cell by external promoters, not shown here. The Green Fluorescent Protein (GFP) product is then used to monitor the output of the promoter by flow cytometry.