Figure 2

Operons provide independent control of gene expression. The framework is measured on a low-copy plasmid in wild type E. coli strain MG1655Z1 containing endogenous AraC levels, and high levels of the repressors LacI and TetR. Fluorescence microscopy snapshots were taken of 500-1000 cells under each combination of saturating inducer concentrations. Each cell within a population is represented by three dots--one for each color--in order to show the cell-cell variability in each condition. For clarity, each cell within a measurement condition is shown using a single dot for each color; individual points are offset horizontally to enable visualization of the entire data set. (A) The autoflourescence of E. coli MG1655Z1 without any fluorescent proteins. (B, C, D, E, F, G, H and I) The response of each reporter to different combinations of the three inducers; each column is one condition with the expected induced colors shown as a bar below.