Saccharomyces cerevisiae Apl2p, a homologue of the mammalian clathrin AP beta subunit, plays a role in clathrin-dependent Golgi functions

Clathrin-coated vesicles mediate selective intracellular protein traffic from the plasma membrane and the trans-Golgi network. At these sites, clathrin-associated protein (AP) complexes have been implicated in both clathrin coat assembly and collection of cargo into nascent vesicles. We have found a gene on yeast chromosome XI that encodes a homologue of the mammalian AP beta subunits. Disruptions of this gene, APl2, and a previously identified beta homologue, APl1, have been engineered in cells expressing wild-type (CHC1) or temperature sensitive (chc1-ts) alleles of the clathrin heavy chain gene. APl1 or APl2 disruptions (apl1 delta or apl2 delta) yield no discernable phenotypes in CHC1 strains, indicating that the Apl proteins are not essential for clathrin function. However, the apl2 delta, but not the apl1 delta, allele enhances the growth and alpha-factor pheromone maturation defects of chc1-ts cells. Disruption of APl2 also partially suppresses the vacuolar sorting defect that occurs in chc1-ts cells immediately after imposition of the non-permissive temperature. These Golgi-specific effects of apl2 delta in chc1-ts cells provide evidence that Apl2p is a component of an AP complex that interacts with clathrin at the Golgi apparatus.