Opposite Roles of the F-Box Protein Rcy1p and the GTPase-Activating Protein Gyp2p During Recycling of Internalized Proteins in Yeast

The F-box protein Rcy1p is part of a non-SCF (Skp1p-cullin-F-box protein) complex involved in recycling of internalized material. Like rcy1(delta), cells lacking the Rab-GTPase Ypt6p or its heterodimeric GEFs Rgp1p and Ric1p are unable to recycle the v-SNARE Snc1p. Here we provide genetic evidence suggesting that Rcy1p is a positive regulator of Ypt6p. Deletion of the GAP Gyp2p restores recycling in rcy1(delta), while overexpression of an active form of Ypt6p partially suppresses the recycling defect of rcy1(delta) cells. Conversely, overexpression of Gyp2p in wild-type cells interferes with recycling of GFP-Snc1p, and the cells accumulate membrane structures as evidenced by electron microscopy. Gyp2p-GFP is distributed throughout the cytoplasm and accumulates in punctate structures, which concentrate in an actin-dependent manner at sites of polarized growth. Taken together, our results suggest that the F-box protein Rcy1p may activate the Ypt6p GTPase module during recycling.