Clathrin and Two Components of the COPII Complex, Sec23p and Sec24p, Could Be Involved in Endocytosis of the Saccharomyces cerevisiae Maltose Transporter

The Saccharomyces cerevisiae maltose transporter is a 12-transmembrane segment protein that under certain physiological conditions is degraded in the vacuole after internalization by endocytosis. Previous studies showed that endocytosis of this protein is dependent on the actin network, is independent of microtubules, and requires the binding of ubiquitin. In this work, we attempted to determine which coat proteins are involved in this endocytosis. Using mutants defective in the heavy chain of clathrin and in several subunits of the COPI and the COPII complexes, we found that clathrin, as well as two cytosolic subunits of COPII, Sec23p and Sec24p, could be involved in internalization of the yeast maltose transporter. The results also indicate that endocytosis of the maltose transporter and of the α-factor receptor could have different requirements.