MEMBRANE-PROTEIN RETENTION IN THE YEAST GOLGI-APPARATUS - DIPEPTIDYL AMINOPEPTIDASE-A IS RETAINED BY A CYTOPLASMIC SIGNAL CONTAINING AROMATIC RESIDUES

The mechanism by which yeast dipeptidyl aminopeptidase (DPAP) A, a typ e II integral membrane protein, is retained in the late Golgi apparatu s has been investigated. Prior work demonstrated that the 118-amino ac id cytoplasmic domain is both necessary and sufficient for Golgi reten tion and that mutant or overexpressed DPAP A no longer retained in the Golgi was delivered directly to the vacuolar membrane (Roberts, C. J. , S. F. Nothwehr, and T. H. Stevens. 1992. J. Cell Biol. 119:69-83). R eplacement of the DPAP A transmembrane domain with a synthetic hydroph obic sequence did not affect either Golgi retention of DPAP A or vacuo lar delivery of the retention-defective form of DPAP A. These results indicate that the DPAP A transmembrane domain is not involved in eithe r Golgi retention or targeting of this membrane protein. A detailed mu tational analysis of the cytoplasmic domain of DPAP A indicated that t he most important elements for retention were within the eight residue stretch 85-92. A 10-amino acid region from DPAP A (81-90) was suffici ent for Golgi retention of alkaline phosphatase, a type II vacuolar me mbrane protein. Detailed mutational analysis within this 10-amino acid sufficient region demonstrated that a Phe-X-Phe-X-Asp motif was absol utely required for efficient retention. The efficiency of Golgi retent ion via the DPAP A signal could be diminished by overexpression of wil d type but not retention-defective versions of Kex2p, another late Gol gi membrane protein, suggesting that multiple Golgi membrane proteins may be retained by a common machinery. These results imply a role for a cytoplasmic signal involving aromatic residues in retention of late Golgi membrane proteins in the yeast Saccharomyces cerevisiae.