Data for: The galactokinase enzyme of yeast senses metabolic flux to stabilize GAL pathway regulation

Nutrient sensors allow cells to adapt their metabolisms to match nutrient
availability by regulating metabolic pathway expression. Many such sensors
are cytosolic receptors that measure intracellular nutrient
concentrations. One might expect that inducing the metabolic pathway that
degrades a nutrient would reduce intracellular nutrient levels,
destabilizing induction. In the galactose-responsive (GAL) pathway of
S. cerevisiae, however, we find that induction is stabilized by flux
sensing. Previously proposed mechanisms for flux sensing postulate the
existence of metabolites whose concentrations correlate with flux. The GAL
pathway flux sensor uses a different principle: the galactokinase Gal1p
both performs the first step in galactose metabolism and reports on flux
by signaling to the GAL repressor, Gal80p. Both Gal1p catalysis and Gal1p
signaling depend on the concentration of the Gal1p-galactose complex and
are therefore directly correlated. Given the simplicity of this mechanism,
flux sensing is likely to be a general feature throughout metabolic
regulation.