Rab GAP cascade regulates dynamics of Ypt6 in the Golgi traffic

Significance The Golgi apparatus functions as the central station of membrane traffic in cells. A series of Rab GTPases, which control various steps in membrane traffic, act consecutively during the course of Golgi maturation. Here, we report that Ypt6, a Rab6 homologue in yeast, resides temporarily at the Golgi and dissociates into the cytosol upon arrival of Ypt32, another Rab GTPase functioning in the late Golgi. We have found that Gyp6, a putative GTPase-activating protein for Ypt6, specifically interacts with Ypt32 as an effector. Taken together with the previously proposed Rab cascade within the Golgi, we propose that multiple Rab cascades interact at the intersection of secretory and endosomal pathways and play significant roles in traffic within and around the Golgi apparatus.