Résumé : The yeast general amino acid permease Gap1 is a convenient model for studying the intracellular trafficking of membrane proteins. Present at the plasma membrane when the nitrogen source is poor, it undergoes ubiquitin-dependent endocytosis and degradation upon addition of a good nitrogen source, e.g., ammonium. It comprises 12 transmembrane domains (TM) flanked by cytosol-facing N- and C-terminal tails (NT, CT). The NT of Gap1 contains the acceptor lysines for ubiquitylation and its CT includes a sequence essential to exit from the endoplasmic reticulum (ER).