Catabolite inactivation of the maltose transporter in nitrogen-starved yeast could be due to the stimulation of general protein turnover.

Addition of glucose to Saccharomyces cerevisiae inactivates the maltose transporter. The general consensus is that this inactivation, called catabolite inactivation, is one of the control mechanisms developed by this organism to use glucose preferentially whenever it is available. Using nitrogen-starved cells (resting cells), it has been shown that glucose triggers endocytosis and degradation of the transporter in the vacuole. We now show that maltose itself triggers inactivation and degradation of its own transporter as efficiently as glucose. This fact, and the observation that glucose inactivates a variety of plasma membrane proteins including glucose transporters themselves, suggests that catabolite inactivation of the maltose transporter in nitrogen-starved cells is not a control mechanism specifically directed to ensure a preferential use of glucose. It is proposed that, in this metabolic condition, inactivation of the maltose transporter might be due to the stimulation of the general protein turnover that follows nitrogen starvation.