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. 2006 Mar 28;4(4):e45. doi: 10.1371/journal.pbio.0040045

Figure 3. Input Function of the Wild-Type lac Promoter Region and Two Variant CRRs .

Figure 3

The input functions describe the promoter activity as a function of the concentrations of the two inducers IPTG (in μM) and cAMP (in mM), measured in midexponential growth in an automated fluorimeter by means of a GFP-promoter fusion on a low-copy plasmid. (A) Surface plot of log wild-type input function. (B) Contour plot of wild-type input function. (C) Schematic drawing showing the activation thresholds and the four plateaus of the input function. (D–F) Same for strain U340, with an OR-like input function. (G–I) Same for strain U339 with an AND-like input function. The plateaus of the input functions are marked by roman numerals in (C, F, and I). Plateau I occurs at zero concentration of inducers, plateau II at saturating cAMP and zero IPTG, plateau III at saturating IPTG and zero cAMP, and plateau IV occurs when both inducers are saturating.