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

UKARYOTIC proteins that are destined for the Golgi, lysosome/vacuole, or plasma membrane are transported through the ER and on to the Golgi apparatus where the pathways leading to the various destinations diverge (Mellman and Simons, 1992) . Sorting decisions made in the Golgi are dependent on positive signals on the proteins being sorted that specify their ultimate location. Proteins not containing positive sorting information will travel through and exit from the Golgi with the bulk flow of lipid via the default pathway. Therefore, proteins that execute their function within the ER or Golgi must have positive signals to specify retention within these organelles. For example, soluble resident proteins of the ER are known to be retained via the four amino acid sequence, K/HDEL, at the COOH terminus (for review see Pelham, 1989) . Receptor proteins that recognize this signal and aid in retaining these proteins in the ER have been identified. In addition, retention signals on ER membrane proteins have also been identified and, thus far, appear to consist of short peptide sequences on the cytoplas-Please address all correspondence to Dr. Tom H. Stevens, Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403. mic side of the membrane (Jackson et al., 1990; Mallabiabarrena et al., 1992) .