Ypt31/32 GTPases and their F-box effector Rcy1 regulate protein recycling by ubiquitination

Ypt/Rab GTPases control all aspects of vesicle transport via their diverse effectors. We have identified the F-box protein Rcy1 as a downstream effector of the Ypt31/32 GTPase pair and showed that together they regulate recycling of proteins through the Golgi apparatus.;We study the mechanism by which Ypt31/32 and Rcy1 regulate this recycling. Because F-box proteins serve as adaptors between specific substrates and ubiquitin ligases, we explored whether Rcy1 mediates ubiquitination of proteins that recycle through the Golgi and whether this ubiquitination is important for the recycling. We used Snc1, a v-SNARE that recycles between the Golgi and the plasma membrane via endosomes, as a recycling marker. We show that Rcy1 physically interacts with Snc1 and regulates its ubiquitination state. Moreover, using an ubiquitination-defective Snc1 mutant protein, we show that ubiquitination is important for Snc1 recycling.;Based on these results we propose a novel role for Ypt/Rab GTPases in the regulation of cargo sorting that involves ubiquitination. This idea is also an extension of the role for ubiquitin-based recycling of PM proteins to include the recycling of proteins to the Golgi.