Clathrin functions in the absence of heterotetrameric adaptors and AP180-related proteins in yeast

The major coat proteins of clathrin-coated vesicles are the clathrin triske lion and heterotetrameric associated protein (AP) complexes. The APs are th ought to be involved in cargo capture and recruitment of clathrin to the me mbrane during endocytosis and sorting in the trans-Golgi network/endosomal system. AP180 is an abundant coat protein in brain clathrin-coated vesicles , and it has potent clathrin assembly activity. In Saccharomyces cerevisiae , there are 13 genes encoding homologs of heterotetrameric AP subunits and two genes encoding AP180-related proteins. To test the model that clathrin function is dependent on the heterotetrameric APs and/or AP180 homologs, ye ast strains containing multiple disruptions in AP subunit genes, as well as in the two YAP180 genes, were constructed. Surprisingly, the AP deletion s trains did not display the phenotypes associated with clathrin deficiency, including slowed growth and endocytosis, defective late Golgi protein reten tion and impaired cytosol to vacuole/autophagy function. Clathrin-coated ve sicles isolated from multiple AP deletion mutants were morphologically indi stinguishable from those from wild-type cells. These results indicate that clathrin function and recruitment onto membranes are not dependent upon het erotetrameric adaptors or AP180 homologs in yeast. Therefore, alternative m echanisms for clathrin assembly and coated vesicle formation, as well as th e role of AP complexes and AP180-related proteins in these processes, must be considered.