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

Since the KDEL receptor would be expected to be continuously trafficking between the IC and the Golgi complex we asked whether this transport step might also be mediated by COP vesicles. We therefore prepared L cells that were either not infected or infected with MHV for 6 h and permeabilized with SLO in the presence of 50 #M GTPTS to facilitate the identification of these COP buds/vesicles. These cells were sectioned and double labeled with antibodies against the KDEL-R and B-COP. After GTP-yS treatment, there was extensive proliferation of buds/vesicles that labeled with anti-B-COP in single labeling studies (not shown). When the sections of this preparation were double-labeled with anti-B-COP and anti-KDEL-R, there was extensive colocalization of the two markers (Fig. 11, A-C) . In MHV-infected cells, many of these buds were continuous with the IC, defined as membrane profiles into which the MHV assemble (Fig. 11 D; see Krijnse-l_x~ker et al., 1994) . Thus, a significant fraction of the COP buds containing detectable amounts of KDEL-R labeling appear to be derived from the IC. The absence of appropriate (early) Golgi markers made it difficult, as in our previous study, to identify the COP buds/vesicles that originate from Golgi compartment(s).