Compartmentation of the Golgi complex: brefeldin-A distinguishes trans- Golgi cisternae from the trans-Golgi network

RCA-I lectin binds to galactose residues present on both N-and O-linked oligosaccharides (1) . To determine if the binding observed was due to the addition of N-linked galactose residues, we carried out a parallel experiment using CHO clone 15B cells that lack the activity of the medial Golgi enzyme, GlcNAc transferase I (20) . In these cells, Figure 3 . Man6P receptors acquire limited sialic acid within the ER of BFA-treated cells. CHO wild type cells were metabolically labeled for 60 rain in the presence or absence of 10 #g/ml BFA and then chased in the presence or absence of BFA for the indicated times. Fresh BFA was added after 4 h to ensure its continued action (13) . Man6P receptors were then isolated by affinity chromatography and applied to slug lectin-Affigel columns. The percentage of man6P receptors eluted from such columns was determined by densitometric scanning of autoradiograms as in Fig. 1 .