Yeast Kex1p is a Golgi-associated membrane protein: deletions in a cytoplasmic targeting domain result in mislocalization to the vacuolar membrane

Mislocalization of membrane proteins to the lysosome does not appear to occur in mammalian systems where mutations that interfere with the localization of ER, Golgi, and lysosomal integral membrane proteins result in their delivery to the plasma membrane (Paabo et al., 1987; Machamer and Rose, 1987; Peters et al., 1990) . One exception to this observation in mammalian systems is the coronavirus E1 protein, a type HI membrane protein normally resident in the Golgi apparatus. Mutations that affect the retention of this protein resulted in delivery to the lysosome rather than to the cell surface (Armstrong et al., 1990) .