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

Kex2p contains an aromatic residue (Tyr) in its cytoplasmic domain that is essential for its efficient retention in the Golgi (Wilcox et al., 1992) . That study combined with our analysis of DPAP A raises the question of whether multiple Golgi membrane proteins are recognized via the same retention "machinery" or whether each membrane protein is recognized and retained by a separate mechanism. To address this (vector with no insert; first two lanes), pCW-KX20 (wild-type Kex2p under control of the GAL/promoter as described by Wilcox et al., 1992 ; WTlanes), pCW-KX21 (derivative of pCW-KX20 containing the Y713A mutation; Y713A lanes), and pCW-KX27 (derivative of pCW-KX20 containing the C-tailA mutation; C-tailA lanes). The ceils were grown overnight in the presence of 2 % galactose, 35S-labeled for 30 min, and chased for 2 h in the presence of 50 #g/ml each of methionine and cysteine, whereupon immunoprecipitation was carried out as in Fig. 6. question we exploited the earlier observation that overproduction of DPAP A caused a portion of DPAP A to be mislocalized to the vacuolar membrane (Roberts et al., 1992) . This result suggested that mislocalization could be achieved by overwhelming the putative Golgi retention machinery with high levels of ligand. If the retention machinery recognizes both DPAP A (or A-ALP) and Kex2p, then overexpression of one protein might lead to mislocalization of the other.