Localization of TGN38 to the trans-Golgi network: involvement of a cytoplasmic tyrosine-containing sequence

To establish the localization of T-G-G at an ultrastructural level, stably transfected CV-1 ceils (Fig. 2 a) were examined by immunoelectron microscopy of frozen sections using an antibody to Tac and protein A-gold particles. Deposition of gold particles was confined to tubules and vesicles on the trans-most face of the Golgi complex ( Fig. 2 b) , consistent with previous morphological descriptions of the TGN (Griffith and Simons, 1986; Geuze and Morre, 1991) . Very little staining of the plasma membrane was apparent in these cells ( Fig. 2 b) , although binding studies with lz~I-labeled anti-Tac revealed the presence of a small amount of T-G-G on the surface of the stably transfected cells ("~60-fold lower than in cells stably expressing Tac; data not shown). Taken together, the immunofluorescence and immunoelectron microscopy studies of cells expressing the T-G-G chimera suggested that the 54-amino acid residues comprising the transmembrane and cytoplasmic domains of TGN38 contained sufficient information for localization to the TGN.