Characterization of the budding compartment of mouse hepatitis virus: evidence that transport from the RER to the Golgi complex requires only one vesicular transport step

In cryo-sections of untreated MHV infected L cells the p58 localized to the budding compartment (Fig. 8 D) as well as to one cisterna of the Golgi stack (not shown). This observation was confirmed in SLO-treated cells where the morphology of the budding compartment became more distinct (Fig. 8 , A-C). There was no obvious difference in the localization of the protein when cells were treated with GTP-yS (see Materials and Methods; Fig. 8 A see below) . We also investigated the localization of another intermediate compartment marker, the small GTPase rab2 (Chavrier et al., 1990) . As shown in Fig. 9 the budding compartment was also significantly labeled for this marker. Of interest in this analysis was the fact that the electron-dense, membranous structures seen clearly in the Epon sections of these preparations (see Fig. 3 A, asterisks) labeled strongly with the anti rab 2.