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. 2011 Apr 29;6(4):e19353. doi: 10.1371/journal.pone.0019353

Figure 1. The gene regulatory network for galactose utilization (redrawn from Bennett et al. (2008) [12]).

Figure 1

The extracellular inputs are [gal]e and [glu]e. The natural output of the network is a group of proteins. The GAL4 protein g 4 binds to upstream activation sites and activates the regulatory genes in the galactose network. The GAL80 gene inhibits the inducing effects of GAL4 and thereby provides negative feedback in the system. GAL3 enhances expression of GAL4 by binding with internal galactose (Gal), forming a GAL3-galactose complex, g 3 c, that inactivates g 80 by binding to it and resulting in a complex g 80 c. In addition, the transporter GAL2 increases the amount of internal galactose, which stimulates the galactose network. We use the GAL1 mRNA level, m1, as the measureable output to control the system. According to sensitivity analysis, the interaction loops involving GAL4p dimerization (the dotted lines) can be eliminated from the original model to create a reduced model.