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

Recently, the retention signals of several Golgi membrane proteins have been analyzed (for review see Machamer, 1991) . In animal cells, membrane protein retention in the cis and medial regions of the Golgi is usually specified by portions of the protein that include the transmembrane domain. Interestingly, the transmembrane domains of the E1 viral glycoprotein (Swift and Machamer, 1991) and galactosyltransferase (Aoki et al., 1992) have been shown to contain uncharged polar residues that appear particularly important for Golgi retention. TGN38, a membrane protein that localizes predominantly to the TGN (Luzio et al., 1990) and cycles between the TGN and the plasma membrane (Reaves et al., 1993) contains a cytoplasmic signal that is both necessary and sufficient for TGN localization (Humphrey et al., 1993) . Therefore, the mechanism of membrane protein retention in the TGN may be fundamentally different from that of other subcompartments within the Golgi.