Hepatitis B surface antigen assembles in a post-ER, pre-Golgi compartment

The model that the assembly of HBsAg occurs in the ER has been based on morphological and immunocytochemical observations and on the assumption that endoglycosidase H sensitivity is restricted to this compartment. Unfortunately, specific markers for the ER have not been used in previous studies and hence the possibility that assembly may take place in an intermediate compartment between the ER and the Golgi has not been addressed. There is biochemical evidence that N-linked oligosaccharides on glycoproteins are still sensitive to endoglycosidase H digestion in such a compartment (Pelham, 1988; Schweizer et al., 1990) . It has also been suggested that oligomerization of some viral proteins may indeed occur in this compartment (Schweizer et al., 1990; Tooze et al., 1988) .