
176 Feedback Control in Systems Biology
Gal2
Gal3
Gal80
Gal2p
Galactose
Gal4pGal4p
Gal4pGal4p
Gal4pGal4p
Gal80p
Gal80p
Gal3pGal3p
Gal3p
Nucleus
Cytoplasm
-
+
+
FIGURE 5.13: Schematic diagram of the galactose signalling pathway, high-
lighting the coupled positive and negative feedback loops.
Due to the pre sence of two feedback loops, the GAL regulatory network
has the potential for ex hibiting multistability. This capability has been evi-
denced exper imentally [15] by g rowing wild-type cells for 12 hours either in
the absence of galactose or in the presence of 2% galactose. In the absence of
galactose, raffinose was used as a carbon source that does not induce ...