Clathrin and two components of the COPII complex, sec23p and sec24p, couldbe involved in endocytosis of the Saccharomyces cerevisiae maltose transporter

The Saccharomyces cerevisiae maltose transporter is a 12-transmembrane segm ent 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 independe nt of microtubules, and requires the binding of ubiquitin, In this work, we attempted to determine which coat proteins are involved in this endocytosi s. Using mutants defective in the heavy chain of clathrin and in several su bunits of the COPI and the COPII complexes, we found that clathrin, as well as hco cytosolic subunits of COPII, Sec23p and Sec23p, could be involved i n internalization of the yeast maltose transporter. The results also indica te that endocytosis of the maltose transporter and of the alpha-factor rece ptor could have different requirements.