Figure 2

Fluorescence levels. The normalized fluorescence, equation 2, in arbitrary units, is shown for cells transformed with: Reporter plasmid without the operator sequence (n = 6); Reporter plasmids with the O₁ (n = 5), O₂ (n = 8), and O_s (n = 10) operator sequence; Repressor plasmids with any of the three operator sequences and Reporter plasmid lacking the lactose operator sequence (n = 10); O₂O₂ induced with 1 mM IPTG (n = 13); O₁O₁ induced with 1 mM (n = 9) and 2 mM (n = 5) IPTG; O_sO_s induced with 1 mM (n = 4) and 8 mM (n = 3) IPTG. In absence of Repressor plasmids, the normalized fluorescence is the same if the Reporter plasmid does not include the operator sequence, or if it includes any of the three operator sequences tested. Co-transformation with a Repressor plasmid and a Reporter plasmid without the operator site causes a decrease in the maximum fluorescence, even if no LacI activity is exerted. The same fluorescence was observed in the O₂O₂ gene circuit at saturating concentrations of IPTG. On the other hand, the maximum fluorescence in the O₁O₁ and O_sO_s gene circuits is statistically different from the maximum value.