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

In MHV-infected L cells, there is considerable amounts of the KDEL-R in the IC, defined as the membrane structures where the virus assembles. To document this point more clearly in uninfected cells, we used an affinity-purified antibody against rabl since preliminary experiments showed that this antibody was an excellent marker of the IC. There is also detectable labeling of the RER (R) in A and D, as well as the nuclear envelope in E. N, nucleus. In D, the large arrowhead points to a possible continuity between the IC and the RER. In E, the large arrowheads denote labeling of a fenestrated cisterna on one (presumably the cis) side of the Golgi stack. Bars, 100 nm. A number of studies have established that the GTP-binding protein rabl or its yeast homologue, YPT-1, is involved in ER to Golgi transport (Schekman, 1992; Tisdale et al., 1992) . In a recent paper, Pind et al. (1994) showed by immunoelectron microscopy that rabl is enriched in the tubular-vesicular structures where the G protein of VSV is enriched when ER to Golgi transport is blocked. By immunofluorescence microscopy these structures colocalized with p58, the marker of the IC. Whereas the well-established markers of the IC such as p58/p53 or rab2 are often in relatively low levels for immunogold labeling, when we tested an affinity-purified antibody against rabl, we noticed that this marker appeared to and p58 (small arrowheads, 10 nm gold). Note the extensive labeling for rabl on the membranes associated with the budding virions (large arrowheads). This labeling extends to parts of the nuclear envelope (B), as well as to one or two Golgi cisternae (C). p58 labels the same structures, albeit with less intensity. The rough ER (R) is relatively poorly labeled for both rabl and p58. A possible continuity between the RER and the IC is indicated in A (large arrow). The asterisk in C shows an electron-dense "vesicular domain" of the IC. Bars, 100 nm. be much more abundant in the IC than the previously used markers.