Membrane protein retention in the yeast Golgi apparatus: dipeptidyl aminopeptidase A is retained by a cytoplasmic signal containing aromatic residues

Although we previously showed that the A85-106 mutation caused DPAP A to be mislocalized to the vacuole (Roberts et al., 1992) , it was not clear whether removal of just F85 Figure 7 . Immunolocalization of DPAP A containing a Phe to Ala mutation at position 85. JHRY20-1A-13A2A cells (stel3A, pep4-3) carrying a 2 /~m plasmid encoding F85A-AAA (pSN128) were stained as in Fig. 3 . DPAP A staining is shown in B, 60-kD V-ATPase subunit staining in C, and a Nomarski image of whole cells in A. and F87, essential for Golgi retention of A-ALP, would lead to mislocalization of the full-length DPAP A protein. Indirect immunofluorescence microscopy was carded out on ste13A cells expressing F85A-AAA, a mutant form of DPAP A in which only the F85 residue was altered (to alanine). Fig. 7 shows that this protein is clearly mislocalized to the vacuolar membrane. A similar result was obtained for the F87A-AAA mutant (data not shown) demonstrating the importance of these residues for retention of wild-type DPAP A.