IDENTIFICATION OF A NOVEL SEQUENCE MEDIATING REGULATED ENDOCYTOSIS OFTHE G-PROTEIN COUPLED ALPHA-PHEROMONE RECEPTOR IN YEAST

The Saccharomyces cerevisiae a-pheromone receptor, a polytopic, G prot ein-coupled, membrane protein, is internalized after binding of alpha- factor. Mutational analysis suggested that the first 39 residues of th e receptor's cytoplasmic tail carries sufficient information for inter nalization. A point mutation in one of these 39 residues, K337 to R337 renders the receptor nonfunctional for endocytosis. Other residues, D 335 and S338, contribute to the efficiency of internalization. When th e sequence DAKSS is added onto a severely truncated receptor, endocyto sis of the receptor is restored, showing that this sequence functions to mediate or to signal interaction with the endocytic machinery. Anal ysis of pheromone response and recovery in strains expressing mutant r eceptors suggests that receptor internalization is not important for r esponse but contributes to recovery from pheromone.