Localization of the Lys, Asp, Glu, Leu tetrapeptide receptor to the Golgi complex and the intermediate compartment in mammalian cells

To unequivocally identify the TGN in an uninfected cultured cell, we used a HeLa cell (SA:48) stably expressing the cDNA encoding the human ot-2,6-sialyl transferase tagged on the lumenal side with the P5D4 epitope (Kreis, 1986) from the cytoplasmic domain of the VSV-G protein. The sialyl transferase is known to be localized to the TGN (Roth et al., 1985) , and this construct is efficiently targeted to the TGN by all criteria tested (Rabouille, C., E Hunte, R. Kieksbusch, E. Berger, G. Warren, and T. Nilsson, manuscript in preparation) . When sections of these cells were double labeled with the anti-KDEL-R and a polyclonal antibody against the G protein tail epitope, the bulk of the KDEL-R did not colocalize with the structures enriched in the sialyltransferase construct (Fig. 10 A) . However, a small, but significant m o u n t of labeling did colocalize (not shown; see Table I/) . In contrast, in SA:48 cells infected with the vaccinia virus recombinant expressing the M protein of MHV, there was significantly higher labeling for the KDEL-R in the trans cisteruae/TGN (Fig. 10, B and C) .