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 a study by Tooze et al. (1988) it was shown that at 31°C MHV was able to bud, but was trapped in the budding compartment in sac(-) cells. Under these conditions the M protein acquired GalNAc only. So far, however, despite multiple attempts, we have not been able to reproduce these observations in our cells. Since it has been shown that, at 15°C, the transport of proteins is blocked just before the cis-Golgi compartment (Saraste and Kuismanen, 1984; Beckers and Balch, 1989) we analyzed the effect of this temperature on the M protein maturation. When cells, pulse-labeled for 2 min at 37°C, were subsequently chased at either 15 or 14.2°C for 1 and 2 h, the M protein acquired GalNAc at both temperatures (Fig. 15 ). After 2 h of chase at 15°C, but not at 14.2°C, some Ms form was also detected, presumably reflecting some leakage at this higher temperature.