Figure 1. Topology and compensated response of the natural network.

(a) Cells with one or two copies of the natural GAL network. For each copy of the network, key network components (GAL4, GAL3 & GAL1, GAL80 and P_GAL1-YFP) are represented by turquoise, blue, red and yellow, respectively. The regulation by GAL4 is indicated by solid turquoise lines and feedback loops are shown by dashed lines. (b) Natural network architecture built by key regulatory components. Coloured ellipses depict proteins, while rectangles show the promoter-gene regions on DNA. Pointed turquoise and blue/red arrows indicate activation and gene expression, respectively, while blunt arrows reflect inhibition. (c) At different galactose concentrations, single-cell expression histograms show the response of diploid S. cerevisae strains carrying the natural GAL network topology (a.u., arbitrary units). At left, diploid strain WP128 with two copies of the natural network; at right, diploid strain WP232 with one copy of the natural network. (d) Fraction of ON cells as a function of galactose concentration from diploid cells carrying one (WP232, light blue) or two (WP128, dark blue) copies of the natural network. Error bars indicate s.e.m. (N=4).