The yeast Snf3 protein has been described to function as a sensor for low concentrations of extracellular glucose. We have found that Snf3 is able to transduce a signal in the complete absence of extracellular glucose. High basal activity of the HXT7 promoter during growth on ethanol required Snf3 as well as other components of the signalling pathway activated by Snf3. Moreover, the C-terminal domain of Snf3 was sufficient to complement the role of Snf3 in this regulation. As the C-terminal tail of Snf3 interacted with other components at the plasma membrane independent of the carbon source, our data suggest that Snf3 is involved in signalling complexes which can be activated by other signals than extracellular glucose.