MODERATE CONCENTRATIONS OF ETHANOL INHIBIT ENDOCYTOSIS OF THE YEAST MALTOSE TRANSPORTER

The maltose transporter in Saccharomyces cerevisiae is degraded in the vacuole after internalization by endocytosis upon nitrogen starvation in the presence of a fermentable substrate, This degradation, known a s catabolite inactivation, is inhibited by the presence of moderate co ncentrations (2 to 6%, vol/vol) of ethanol, We have investigated the m echanism of this inactivation and have found that it is due to the inh ibition of the internalization of the transporter by endocytosis. The results also indicate that this inhibition is due to alterations produ ced by ethanol in the organization of the plasma membrane which also a ffects to endocytosis of other plasma membrane proteins. Apparently, e ndocytosis is particularly sensitive to these alterations compared wit h other processes occurring at the plasma membrane.