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

Proteins that enter the secretory pathway are thought to be transported to the cell surface by default via a "bulk flow" mechanism unless they contain additional targeting information (Pfeffer and Rothman, 1987; Rothman, 1987; Wieland et al., 1987; Karrenbauer et al., 1990) . Such targeting information is found in soluble proteins resident in the ER which maintain their localization by containing a retention signal at their carboxy termini (Munro and Pelham, 1987; Pelham et al., 1988) . Deletion of the retention signal results in secretion of the soluble ER resident proteins to the cell surface. Soluble proteins destined for the mammalian lysosome re-A. Cooper's present address is the Institute of Molecular Biology, University of Oregon, Eugene, OR 97403.