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

Because the staining procedure depends on separate amplification of two rabbit primary antibodies (Franzusoff et al., 1991; see Materials and Methods) , control experiments were performed to ensure a lack of secondary antibody cross reactivity. No Kex2p staining was observed in a kex2A strain lacking Kex2p (Fig. 4 B) , and similarly no A-ALP staining was observed in phoSA strains lacking the A-ALP fusion protein (Fig. 4 C) . Moreover, when the procedure was applied to a strain expressing Kex2p and wild-type ALP, a vacuolar membrane protein, the staining patterns were distinct, further demonstrating a lack of cross reactivity of the two rabbit antibodies (Fig. 4 D) . Finally, when either primary antibody was omitted from the procedure no significant staining was observed for either corresponding antigen (data not shown).